Wheel Bearing Diagnostic Tips

Wheel Bearing Diagnostic Tips

Problem:

Coming up with an accurate diagnosis for unitized style wheel bearing.

Cause:

The sealed design of the wheel bearing sometimes makes identifying which bearing is the source of the complaint difficult.

Solution:

There are several techniques available that can help pinpoint a failing bearing. They are listed below:

Test Drive

Wheel bearings can cause many different types of noises when driving. The noise will usually be more pronounced when the bearing is in a loaded condition, such as during a turn.

Vibration Test

Failing wheel bearings will often cause a roughness during wheel rotation. The vehicle’s strut and spring act like an amplifier and allow easy diagnosis of a rough bearing. Place your hand on the spring and rotate the wheel assembly. A rough bearing will produce a pronounced vibration through the spring. Repeat the procedure on the opposite side.

Stethoscope Test

Failing bearings will often make a noise when they start to fail. The noise is not always easy to identify. The use of a stethoscope can make pinpointing the problem bearing easier. Once the vehicle is both on the rack and in gear, you can use the stethoscope. Start by placing the stethoscope on the knuckle as close to the bearing as possible. If the bearing is failing, it will produce a noticeable hum or grinding sound. It may be necessary to turn the wheel slightly to duplicate the bearing noise on the rack.

Caution: It is essential to take extreme care when working near a rotating wheel.

Isolation Test

In some cases, it will be necessary to isolate the bearing to determine its condition. For instance, for most FWD vehicles, this is a relatively straightforward process. First, remove the caliper and rotor. Next, disconnect the outer tie rod end and low ball joint. Continue by removing the CV axle nut. Next, disconnect the knuckle from the lower ball joint and remove the CV joint from the hub. The bearing is now isolated. Finally, rotate the bearing while feeling for roughness.

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Identifying When Self-Adjustment Takes Place on Drum Brake Vehicles

Identifying When Self-Adjustment Takes Place on Drum Brake Vehicles

The purpose of this article is to help mechanics like you avoid improper rear drum brake adjustments. As you read, take note of the different common mistakes and how to stay away from them. Likewise, you may notice that there are several ways to ensure a quality job.

Rear Drum Brake Adjustments

One common problem when dealing with rear drum brakes is that mechanics don’t understand when and how self-adjustment occurs. As a result, improper adjustments can occur. On the other hand, learning to identify the self-adjusting parts and when they operate will allow the following:

  • Determining whether the self-adjusting mechanism is operating as designed.
  • Allow proper assembly or repair of self-adjustment mechanism
  • Identify when self-adjustment takes place

Duo-Servo Drum Brake

You can identify duo-servo drum brakes by the location of either the self-adjuster or anchor pin. Likewise, the location of the self-adjuster is at the bottom between the primary and secondary brake shoes. Likewise, the anchor pin is at the top between the two brake shoes.

All duo-servo drum brakes are designed to self-adjust when backing up only under the following conditions:

  • There is a large enough gap between the secondary brake shoe and the brake drum.
  • The parts that make up the self-adjusting mechanism are operating correctly.

When servicing vehicles with duo-servo drum brakes, it is essential to make sure all parts are lubricated and installed correctly.

 

Non-Servo Drum Brake

Often times FWD vehicles have non-servo drum brakes. As a result, the most distinguishing feature of a non-servo drum brake is the location of the anchor pin. For example, the anchor pin on non-servo drum brakes is at the bottom of the backing plate.

There are two techniques used to allow self-adjustment on non-servo drum brakes. The most common is during any forward braking. For the vast majority of FWD vehicles use this method. There are a small number of non-servo drum brakes that use the parking brake to self-adjust.

A good rule of thumb is to use the self-adjuster’s location to help determine when self-adjustment takes place. In the case that you notice that the self-adjuster is part of the strut rod self-adjustment occurs during forward braking. For instance, If the self-adjuster is part of the parking brake lever then self-adjustment occurs during parking brake use.

While these rules of thumb are pretty accurate, they do not apply to all cases. Another way to determine when self-adjustment takes place is to engage both methods and see which one works.

Figure 60.1

Figure 60.1

Figure 60.2

Figure 60.2

Figure 60.3

Figure 60.3

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Brake Hose Tips

Brake Hose Tips

Brake Hose Problems

Internal brake hose damage during inspection or service

Brake Hose Problem 1:

Use of non-approved hose clamping devices such as vise grips (See Figure 58.1) Vise grips or similar tools can permanently damage the internal structure of even a new  hose.

Vice grips on a brake line

Brake Hose Problem 2:

Hanging caliper by the hose during inspection or service as shown in Figure 58.2. Hanging a caliper by the hose puts undue stress on the internal structure of the hose and can cause permanent damage. Some light truck calipers weigh as much as 18lbs. Calipers should be supported during service, as shown in Figure 58.3.

Cause Solution 1:

Use an alternate method for preventing fluid loss during service such as:

  • Use a tire valve stem to plug the brake hose at the banjo bolt opening.
  • Change the caliper only when the replacement part is available to prevent excessive fluid loss.

Cause 2 Solution:

Support caliper during inspection and service using pipe hook or another suitable tool. Do not rest the caliper on suspension or frame as it will probably fall off and could create even more damage to the hose.

More Info: The brake hose is made up of a series of layers of rubber and a woven fabric. These layers give the hose the ability to withstand high pressures and prevent leaking. Failure to properly handle the hoses during inspection or service can result in ether a restricted hose or a one way check-valve condition.

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Brake Pull Diagnosis

Brake Pull Diagnosis

Problem

Brake pull occurs when a vehicle pulls to one side or the other during braking.

Cause

Depending on several variables, there are a variety of potential causes for brake pull. For example, most of the common causes have been listed below:

  • Friction problem
  • Rotor friction surface problem
  • Caliper problem
  • Restricted brake hose
  • Hydraulic restriction higher than brake hose
  • Rear brake imbalance
  • Loose front end part
  • Alignment
  • Tires

 

Solution

Determining the actual cause of the pull condition relies on methodically approaching the problem. When faced with a brake pull condition, follow these steps:

 

1. Confirm Brake Pull

First, drive the vehicle on typically crowned roads. Next, take note of how the vehicle handles both braking and non-braking. If you notice any brake pull, proceed to the next step.

Red truck with brake pull

2. Test more parts to rule out brake pull

Before jumping to conclusions, it is essential to check tire size, condition, and air pressure. If any tires are not within acceptable levels, side to side swap tires accordingly and road test the vehicle. Otherwise, if the pull is still present, go to the next step.

3. Inspect steering and suspension

Pay close attention to any part that will allow a toe or caster change during braking. If any component shows excessive wear that could contribute to the pull, the repair is suggested before continuing. Otherwise, if all front-end parts are tight, go to the next step.

4. Line lock test

Line lock rear brakes with approved line lock. Test drive vehicle to check if the pull is affected. If the pull is gone, the cause is in rear brakes. If the pull is still present go to the next step.

5. Brake Inspection for brake pull

Pay close attention to the operation of the calipers. Check caliper housing’s ability to move freely. Next, check piston condition by pulling back dust boot to see if a significant difference exists from side to side service calipers and road test vehicles. If the pull is still present, go to the next step.

6. Swap brake pads

In the case that the front pads have friction material left on them, swap brake pads from side to side and test drive the vehicle. If the pull is gone or switches, directions friction is the source of your problem. If there is no change in the pull, swap the brake pads back to their original position and go to the next step.

7. Swap Rotors

With brake pads back to their original position, swap rotors, and test drive vehicle. If the pull is gone or switches sides rotor’s friction surface is the cause. If there is no change in the pull go to the next step.

 

8. Brake pull Side-to-side pressure check

If pressure gauges or clamping plate gauges are available, perform aside to side pressure check. Pressure readings should be within 50psi at a pressure above 500psi. If pressure readings are not within 50psi of one another, go to the next step, or if pressure gauges are not available to proceed to the next step.

 

9. Determine brake pull restriction points

Determine possible points of restriction. On a front to rear split hydraulic system this will include the brake hose, ABS modulator (if equipped), and combination valve (rare but possible), and steel brake line to the side opposite the direction of the pull. If the diagonal split hydraulic system, the list will include brake hose, ABS modulator (if equipped), steel brake line to the side opposite the direction of the pull, and master cylinder.

10. Brake hoses and brake pull

The most common point of restriction is the brake hoses. The hose on the side opposite the direction of pull is the most likely cause. If the hose has a mounting bracket clamped around it, check the bracket for signs of corrosion. When corrosion is present, pry the bracket apart, squeeze the hose in the direction opposite the crushed pattern and then test drive the vehicle.

In the case that the pull is eliminated or substantially reduced, the brake hose is the cause. If no external signs of restriction are visible, the decision must be made to replace the hose(s) or perform additional diagnostic steps. Those steps could include switching hoses from side to side or blowing through both hoses to check if there is a difference.

Usually, the time necessary to do either test would be better spent trying a new set of hoses. If the hoses are shown not to cause the pull by diagnosis or replacement, the system should be checked for an upstream restriction. Go to the next step.

11. Hydraulic components

Brake pull still present after performing steps 1 to 10 – This should not happen very often. If you followed steps 1 to 10 correctly and the vehicle is still exhibiting a brake pull, identify hydraulic components between the master cylinder and front brakes.

These will usually include the ABS modulator and/or the combination valve. On vehicles equipped with combination valves, the outlet lines of the valve can switch using the necessary line adapters to determine if the valve is the source of restriction. If the pull is still present after step 11, it is advisable to recheck previous actions.

 
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Diagnosing Two Wheel Drag – Disc Brakes

Diagnosing Two Wheel Drag – Disc Brakes

Problem

Both front wheels are experiencing wheel drag.

Cause of Two Wheel Drag

Residual pressure causing brakes to apply after brakes reach operating temperature. As a result, the most common cause for this condition comes from plugged or covered vent ports in the master cylinder.

Two Wheel Drag Solution

The first step to fixing two-wheel drag is to identify the cause of the residual pressure. As you’ll see, when presented with a two-wheel drag complaint, the diagnostic process starts under the hood, not at the wheel. Similarly, both wheels having the same symptom rules out the calipers and brake hoses as likely causes. The cause will almost always be something similar to both wheels (See Figure 55.1).

NOTE: Before proceeding with diagnosis check the system for contamination.

You will need to duplicate the system before the diagnosis can continue. To begin, take the vehicle for a test drive to bring the brakes up to operating temperature. When performing this step, it is best to follow the advice below:
 
Diagram
  • First, be sure to stay close to the shop.
  • Next, take a line wrench (If the drag increases to a non-drivable point, you’ll be glad you have it.)
  • Finally, do not “hammer” the brakes during the test drive. Make numerous stops in city driving until you either feel the drag or know the brakes are at operating temperature.

Diagnosing Two Wheel Drag

1. Once the brakes are at operating temperature or the drag has been duplicated, rack the vehicle and leave it neutral.

 

2. Check all four wheels for drag. If necessary, measure drag.

 

3.  Drag on front brakes (or front and rear on four-wheel disc brake-equipped vehicles) – first, start by loosening the master cylinder away from the vacuum booster by ¼” . Check effect on drag condition. If drag is still present, go to the next step. If drag is released, go to step eight.

 

4. Drag still present with master away from booster – Loosen the brake line(s) supplying the dragging brakes. Check effect on drag. If drag is released, there is an internal problem in the master cylinder. You’ll either have plugged vent port(s) or a binding piston(s) in the bore. Master cylinder replacement is required. If drag is not released, go to the next step.

 

5. Drag is not released after brake lines at master cylinder are loosened. First, locate the next component downstream from the master cylinder. Likewise, trace the brake lines from the front wheels to that component. Next, loosen outlet lines of components that supply the dragging brakes. If drag is released component is the source of restriction and requires replacement. If drag is not released, go to the next step.

Drag Not Releasing

6.  Drag is not released after loosening brake lines at the outlet of the component between the master cylinder and dragging brakes. Trace lines to dragging brakes. For instance, is there another component between the component tested in step 5 and dragging brakes? If yes, repeat step 5 on that component. If no, go to the next step.

7.  Wheel drag still present on both wheels after performing steps 3 through 6. Open bleeder screws on both front calipers and check the effect on drag condition. If either wheel frees up, the brake hose on that wheel acts as a one-way check valve. If either or both wheels fail to release, the problem is a mechanical problem with both front calipers. Inspect and service as required.

8. Wheels released after the master cylinder was moved away from the vacuum booster. The problem is in front of the master cylinder. Something is not allowing pistons in the master cylinder to return to a fully released position resulting in the cup seals covering the vent ports. The list of possible causes varies from vehicle to vehicle-based on system configuration. Here is a list of possible causes (see Figure 55.2):

Diagram 2

Possible Causes of Two Wheel Drag

  • Stoplight switch adjustment.
  • Binding pedal linkage  – check for unrestricted movement. If necessary, disconnect the booster pushrod.
  • Pedal height adjustment – some import vehicles have an adjustable link between the brake pedal and booster.
  • Vacuum booster applying partial assist – air and vacuum valves inside booster may not be returning to their proper position when the brake pedal is released. Likewise, pull the one-way check valve out of booster with drag present to check for this condition.
  • The adjustable pushrod on the booster is too long.

NOTE: Most 2 wheel drag problems will come from a problem in front of the master cylinder as described above or by the master cylinder itself. Likewise, problems below the master cylinder rarely cause Two-wheel drag problems.

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One Wheel Drag Diagnosis – Disc Brake

One Wheel Drag Diagnosis – Disc Brake

Problem

One wheel drag on disc brakes.

Cause of One Wheel Drag

There are several different possible causes for one wheel drag. The cause of a one-wheel drag on a disc brake can be either mechanical or hydraulic. The list of possible causes will include:

  • Caliper slides
  • Caliper piston
  • Check valve brake hose
  • Restriction in ABS modulator (if equipped)
  • Plugged or covered vent port (FWD only)

One Wheel Drag Solution

Applying a systematic approach to the diagnosis of a one-wheel drag condition will determine the cause. The diagnosis’s objective is to determine if the source is mechanical or hydraulic but to determine the actual cause.

To diagnose a one wheel drag on a disc brake, follow the steps below:

 

1. Duplicate the problem. Confirm the problem before continuing. If necessary, measure wheel drag.

 

2. Loosen the brake line fitting at the INLET end of the brake hose supplying the dragging wheel. Check the drag condition if the drag releases; go to step 5. If the drag is still present, go to the next step.

NOTE: If it is impossible to loosen the brake hose inlet fitting go to the next fitting upstream. You can usually find a fitting higher than the hose you can loosen without damaging the brake line.

3. Tighten brake line fitting. Loosen bleeder screw on dragging caliper. If the drag releases, the brake hose is the source of the problem and requires replacement. It is acting as a one-way check valve. Fluid is allowed to the caliper on applying but not allowing full release (see Figure 54.1). If the drag does not release, go to the next step.

Brake diagram

Figure 54.1

One Wheel Drag - Steps 4-7

4. If drag is still present after steps 1 to 3, the problem is mechanical in nature. The caliper piston or caliper slides are causing the drag. An inspection of the caliper should yield the source.

5. If drag is releasing after step 2, tighten the fitting and duplicate the problem. Locate the next component higher than the brake hose. This will most likely be the ABS modulator. With the wheel drag present, loosen the inlet brake line supplying the dragging wheel. Check effect on drag. If drag does not release, go to the next step. If drag does release, go to step 7.

6. Drag does not release after step 5 – loosen outlet brake line fitting at ABS modulator (or another component). Check drag. If released, the restriction is in the ABS modulator, and modulator replacement is required.

7. If drag is releasing after step 5 – tighten brake line fitting at the ABS modulator. Duplicate drag condition. Loosen inlet brake line fitting on next component upstream. This will usually be the combination valve on RWD vehicles and the master cylinder on FWD vehicles (See Figure 54.2) if the combination valve goes to step 8 if the master cylinder on the FWD vehicle goes to step 9.

One Wheel Drag - Steps 8-10

8. Combination valve on RWD vehicles – If loosening the inlet on the combination valve released, the drag goes to step 9. If wheel drag is still present, loosen the outlet line on the combination valve that supplies the dragging wheel. If the wheel releases, a combination valve is the source of restriction and will need replacing.

9. Tighten all fittings and identical drag conditions. With drag condition present, loosen master cylinder from power assist unit by at least ¼”. Check drag. If drag releases problem is in front of the master cylinder. This could include stoplight switch adjustment, pushrod adjustment, partial assist condition, or pedal height adjustment. If the drag condition is still present, go to step 10.

10. With drag condition present, loosen brake line fitting at master cylinder outlet supplying dragging brake. If the wheel frees up master cylinder is the source of drag and will require replacement.

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Measuring Wheel Drag

Measuring Wheel Drag

Wheel Drag: The Problem

Accurately determining wheel drag during diagnosis

The Cause of Misdiagnosed Wheel Drag:

Many mechanics judge the amount of drag by rotating the tire/wheel assembly by hand, which is not always an accurate method of determining drag.

How to Measure Drag:

When diagnosing the cause of a drag check, it is essential to accurately determine if the results of a test step impacted the amount of drag. Some drag conditions result in only a slight drag, making diagnosis more difficult.

The most accurate method to determine the drag on a wheel is to use an inch-pound torque wrench. This method is also the best method to use when trying to determine the amount of change on drag during a diagnostic test. To perform a drag test using an inch-pound torque wrench, follow the steps below:

1. Duplicate the drag condition
2. Adjust the torque wrench to a midway setting such as 30 (Figure 53.1)

Torque Wrench set to mid setting

53.1

3. Position a wheel stud to the three o’clock position as shown in Figure 53.2

Wheel stud at 3'oclock

4. Place the torque wrench on the lug nut at the three o’clock position.

5. Attempt to rotate the tire/wheel assembly while noting whether or not the torque wrench clicks. If the torque wrench clicks before the wheel turn, go to the next step. If the torque wrench does not click before the wheel rotates, go to step 7.

6. Torque wrench clicks before wheel rotates – adjust the torque wrench to a higher setting and attempt to turn the wheel. A good rule of thumb is to increase it by 10. Repeat this step until the wheel rotates when the torque wrench clicks.

7. Wheel rotates before torque wrench clicks – adjust the torque wrench down and rotate the wheel. A good rule of thumb is to decrease it by 10. Repeat this step until the wheel turns when the torque wrench clicks.

TIP: When diagnosing a one-wheel drag condition, measure the drag on the opposite (non-dragging) wheel to use as a comparison. When performing diagnostic steps to determine the cause of a drag, use the opposite wheel’s drag measurement to determine if the dragging wheel is completely releasing. See page 94 for one-wheel drag diagnosis

Tip: while most wheel drag problems are easy to identify some are not. Knowing how to determine the amount of drag is necessary when diagnosing certain types of problems.

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Red Brake Warning Light On

Red Brake Warning Light On

Problem:

This article will go over what to do when the red brake warning light comes on after service on vehicles equipped with pressure differential switch.

Red Brake Warning Light - Cause:

The pressure differential switch piston is offset, causing the pressure differential switch to remain in a grounded position.

How to Fix the Red Brake Warning Light:

The solution applied will depend on what type of pressure differential switch the vehicle has. Most pressure differential switches have only one function – turn the red warning light on if a hydraulic failure occurs in either the primary or secondary circuits. Some others have the additional function of limiting fluid loss to the rear brake circuit in a rear circuit failure.

Conventional pressure differential switch (fluid flow to rear brake):

Bleed the system using the manufacturer’s sequence until all the air is out of the system. If the pressure differential switch does not re-center itself during bleeding, it creates a pressure loss opposite the original hydraulic failure. For example, if the initial failure were a broken rear brake line, you would open either front bleeder to create this difference.

Once open, spike the brake pedal a couple of times while watching the red warning light (key on), using caution not to exceed ¾ pedal travel to prevent master cylinder damage. The pressure difference should push the piston back to the center.

Special purpose pressure differential switch (restricted fluid flow to rear brakes):

This type of pressure differential switch will not allow a system to bleed until the piston is re-centered. To re-center, bleed the system from the master cylinder down to the valve’s inlet until you can no longer see air. Accomplish this by cracking the line fitting at both the master outlet and valve inlet.

Once bled, spike the brake pedal a couple of times while watching the red warning light (key on), using caution not to exceed ¾ pedal travel to prevent master cylinder damage. The pressure difference should push the piston back to the center. Once re-centered, complete the repair by bleeding the rear brakes.

More Info on Red Brake Warning Light:

To better understand the fix, an understanding of the pressure differential switch’s function is in order. Figure 51.1 is a cross-sectional view of a stand-alone pressure differential switch. The pressure differential switch consists of a piston exposed to primary and secondary circuit pressures and a normally open switch. The switch consists of the switch body, a spring-loaded plunger, and a contact pin.

Tip: Knowing what can turn the red brake light on is the first step in determining how to get it to go off.
Schematic

51.1

The piston has what is called a detent in the center of it. The detent is a beveled indentation where the switch plunger rests. The switch plunger is held in place by the spring tension of the switch.

Each end of the piston is fitted with o-rings to form a seal from the primary and secondary circuit pressures. One end of the piston is exposed to primary circuit pressures, while the opposite end has exposure to secondary circuit pressures.

Regular system operation produces near equal pressures in both the primary and secondary hydraulic circuits. The spring-loaded plunger on the switch keeps the piston from moving under minor pressure differences. Typically it will prevent movement until the pressure difference reaches approximately 150 psi.

If a hydraulic failure occurs in either the primary or secondary circuits, it will create a pressure difference. The high pressure on one side of the piston will push the piston towards the failed side or low-pressure circuit (See Figure 51.2).

The movement of the piston will cause the open switch to go to a closed position which completes the ground to the red warning light. The light will remain on until the piston is re-centered.

Figure 51.2

Hydraulic Failure Causing Red Brake Warning Light

Most vehicles will never experience a hydraulic failure, and therefore the pressure differential piston will never move. This lack of movement is responsible for the piston “sticking” when offset due to a hydraulic failure. The piston bore corrodes and causes an interference fit.
Special Purpose Pressure Differential Switches

A group of specialized pressure differential switches has an additional function in a rear circuit failure. In addition to turning the red warning light on, they also restrict fluid flow to the rear brakes in the rear circuit hydraulic failure vent.

A typical method is in Figure 51.3. Figure 51.3 shows the piston in the neutral position. Fluid flow to the rear brakes is through the passages marked as such. Figure 51.4 shows what happens to these passages when a rear circuit hydraulic failure occurs. The piston offsets and covers the holes. As a result, fluid flow will be restricted to the rear circuit, limiting fluid loss.

Fluid passages to rear brakes

51.3

51.4

If a rear circuit hydraulic failure occurs and the piston does not re-center, the rear brakes will not be bled until the piston is re-centered. See procedure under “Solution.”

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Metering Valve Diagnosis

Metering Valve Diagnosis

Problem:

If you’re experiencing premature pad wear, nose-diving, or lack of stopping power on vehicles equipped with a metering valve, this is the right article for you.

Metering Valve Cause:

As you consider the cause of any of the problems above, it is essential to add the metering valve to the list of possible reasons for the above issues. The symptoms produced by failed metering valves will depend on the type of failure and type of vehicle. Here is a description of each type of failure:

1 – Valve stuck OPEN: If the valve is stuck open, the vehicle will have instant-on front brakes (See figure 48.1). The front brakes will apply instantly, while the rear brakes will have to “play catch up.” The long-term symptom of instant-on front brakes is premature front pad wear on all pads. Depending on the vehicle, this condition may also cause the vehicle to nose dive when stopping. This symptom does not always present itself with valve failure.

Corroded stem cap

48.1

2 – Valve stuck where it can’t open completely: if the restriction in the valve’s movement is such that it can only open partway or seized in this position, the vehicle will only have partial front braking. The typical complaint from the driver will be a lack of stopping power.

Metering Valve Solution:

The metering valve should be one of the first things checked when diagnosing the above complaints. The reason for this is it will be one of the easiest things to check. Perform the following steps to verify metering valve function:

1 – Locate the metering valve. It will either be under the vehicle or the hood. Check the external condition of the cap screw–stem area as shown in Figures 48.2 & 48.3.

Figure 48.2 shows an underhood valve. Metering valves located under the hood rarely fail because of the protection they have from the elements. This valve does not need checking. The valve in Figure 48.3 is mounted under the vehicle and receives exposure to the elements. The cap screw and stem have been bonded together by the corrosion.

Metering Valve

48.2

48.3

2 – If the metering valve is in question, check it by having someone apply the brake pedal while watching the metering valve stem. The stem should move out on use and in on release, as shown in Figures 48.4 & 48.5.

Metering Valve

48.4

Metering Valve Stem Out

48.5

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Proportioning Valve Diagnosis

Proportioning Valve Diagnosis

Problem

Determining when and why to add the proportioning valves to the possible causes of the problem being diagnosed.

Cause

Not understanding the proportioning valve can result in the valve being added to the list of possible cases when it cannot cause the diagnosed problem or add it to the list when it should be.

Solution

 The proportioning valve is there to prevent rear-wheel lockup during panic braking. Its two main reasons are 1. most vehicles use drum brakes in the rear, and 2. all vehicles experience weight transfer during a panic stop. Rear drum brakes are hydraulic over mechanical in design.

If applying too much pressure to the wheel cylinders, lockup will occur. All vehicles with rear drum and rear disc brakes will experience weight transfer during a panic stop. When taking off the rear wheels’ weight during a panic stop, the tendency for the rear brakes to lock up will increase. The design of the proportioning valve is there to limit the pressure to the rear brakes during a panic braking situation.

When do proportioning valves work?

The most crucial point to understand about proportioning valves is when they work – only during panic braking. This means that a vehicle could potentially go its whole life without ever using its proportioning valve. Located between the master cylinder and rear brakes, the conventional proportioning valves are hydraulically activated.

Vehicles with front-to-back split hydraulic systems have one, while diagonal splits systems require two because each rear wheel is on a separate hydraulic circuit. The proportioning valve may be a stand-alone valve, part of the combination valve, or built into the master cylinder.

Deeper Inspection

Whether or not you take the additional steps to inspect or diagnose a vehicle’s hydraulic proportioning valve will depend on the following:
 
  • Could the customer’s complaint involve the proportioning valve?
  • What is the condition and location of the combination valve?
  • What type of proportioning valve does the vehicle have?
The only time that the proportioning valve should be on our list of possible causes if the customer’s complaint involves rear wheel lockup under panic braking. We must ask the customer when the rear wheel lockup is occurring – light to regular or heavy to panic braking?
 
If the answer is panic braking, the valve is on our list, but it won’t be the only thing on our list (See pg 104 for more information on rear wheel lockup). The valve’s design will determine how and when we are going to diagnose it.
 

Proportioning Valve Cap Screw

The design of some proportioning valves allows two things – more chance for failure and an easy way to diagnose them. If we look at the proportioning valve in Figure 49.1, we will see the cap screw that holds the piston and spring in place is vented.

The vent hole is a small rubber “mushroom” that prevents moisture from entering the cap screw. If this valve style is mounted low on the vehicle, as in most rear-wheel drive vehicles, it can introduce a high degree of moisture.

This is especially true in areas that use road salts for snow and ice removal. The moisture can corrode the cap screw and allow water to enter into where the piston travels in the cap screw (See Figure 49.2). This causes the cap screw to rust, which bonds the piston and cap screw together (See Figure 49.3).

Typically after removing the cap screw, the cap screw, spring, and piston are separate pieces. This corrosion prevents the piston from moving when a panic braking situation occurs.

Proportioning Valve

49.1

Cap Screw Vent

49.2

Piston Cap Screw

49.3

Checking the Proportioning Valves

The same thing that allows the valve to fail will enable us to check it – the cap screw vent hole. First, determine if the valve is a good candidate by its external appearance. If corrosion occurs outside the valve or the cap screw, it is a good candidate. Remove the rubber mushroom from the cap screw.

Next, insert a paper clip to the bottoms out of the piston, as in Figure 49.4. Have an assistant start the vehicle and apply heavy pedal pressure to simulate a panic braking situation. The paper clip should push against you and travel about 1/32” to 1/16” as the piston moves. If the paper clip doesn’t move, the piston has seized in the cap screw, and the valve will need replacing. This test will work on any proportioning valve vented through the cap screw and should be part of your standard inspection if the valve’s exterior condition merits it.

Checking the Proportioning Valves (Not Vented)

Bottom paper clip against piston

Many proportioning valves are not vented through the cap screw. There is not a quick check for these types of valves. These valves should only be checked if the customer’s complaint indicates a possible proportioning valve problem. Most shops do not have pressure gauges, so diagnosing the issue will have to be eliminated. You should check all other possible causes before condemning the proportioning valve.

Pressure gauges are the best way to diagnose a failed proportioning valve. There will be a gage installed into the front and rear hydraulic circuits. Start the vehicle, and apply the brake pedal with heavy pedal pressure to duplicate a panic braking situation. The front and rear pressures should be different. Most manufacturers do not publish these pressures. The rear brakes usually are “shut” down between 500psi and 800psi, while the fronts can climb to well over 1500psi See Figures 49.5, 49.6, and 49.7).

What you are looking for is whether the rear pressure has any limitation. If the rear pressure is over 1000psi and is close to or equal to the front pressure, then the valve is not working and will have to be replaced to correct the problem.

Proportioning valve operation - Normal braking

49.5

Knee Point

49.6

49.7

Proportioning Valves Rules of Thumb

Using the definition of the proportioning valve’s function and our understanding of system operation, we can use the following rules of thumb:

 

  • On the front to rear split hydraulic systems, a failed proportioning valve should cause both rear wheels to lock up under panic braking – unless one rear brake has a condition that will prevent this (i.e., severely out of adjustment or seized wheel cylinder).
  • On diagonal split hydraulic systems (FWD), it will be infrequent for both proportioning valves to fail simultaneously. If both rear wheels are locking under heavy to panic, look at mechanical causes before condemning the proportioning valves.

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Brake Valve Identification

Brake Valve Identification

Brake Valve Problem:

Determining whether to add the vehicle’s brake valve(s) to the list of possible causes.

The Cause of Difficulty in Brake Valves:

Brake valves represent the least understood of all the base brake components. Not knowing what the various brakes do, when they do, and how they do it can lead to misdiagnosis.

Brake Valve Solution:

Brake valves are the least understood of all conventional brake components. By understanding what brake valves a vehicle has is essential to the accurate diagnosis of specific brake problems. Because of this, a technician should determine a vehicle’s brake valves by knowing the hydraulic system the car has and looking at the valve itself.

Determining a vehicle’s hydraulic system is very easy on most vehicles. For example, FWD vehicles have diagonal split hydraulic systems (See Figure 47.1). As a result, a diagonal split hydraulic system connects each front wheel with the opposite rear wheel. Likewise, the majority of RWD vehicles have front to rear split hydraulic systems (See Figure 47.2). In a front-to-rear split hydraulic system, the front section is connected hydraulically to one half of the tandem master cylinder while the rear section connects to the other half.

There are some exceptions where RWD vehicles have diagonal split hydraulic systems. Fords and Lincolns are the most common of these exceptions. The easiest way to determine the system is to look at the rear brake lines. For example, if the brake lines from each rear wheel come together into a central line, the vehicle has a front to the rear split hydraulic system. If each rear line continues to the front of the vehicle, the system is a diagonal split hydraulic system.

Schematic 1 - image 47.1

47.1

Schematic 2 - image 47.2

47.2

Looking at Brake Valve

The next step in identifying the type of brake valve(s) a vehicle has involves looking at the brake valve(s). For example, the majority of late-model cars use combination valves. A combination valve is a valve that “combines” more than one valve into a standard housing. Similarly to above, determining the combination valve involves a simple inspection process.

Figure 47.3 shows two typical RWD combination valves. These valves house three separate valves in ordinary housing. The first and easiest valve to identify in this type of valve is the pressure differential switch. The pressure differential switch is in the center of the combination valve (Labeled as “B” in Figure 47.3). The plastic switch identifies it. Any conventional brake valve with this type of switch is a pressure differential switch. For example, the pressure differential switch will complete ground to the red brake warning light in a hydraulic failure.

ABC

47.3

The next valve to determine will be the valve between the master cylinder and rear brakes. To do this, trace the line from the rear brakes to the combination valve. As you find the end of the valve, you’ll see that it houses the proportioning valve. The proportioning valve prevents rear wheel lockup during panic braking. A hydraulic activated valve starts limiting the pressure to the rear brakes at a certain point called the “knee point.” The proportioning valves have the “C” label in Figures 47.3.

Metering Brake Valve

proportioning valve to front brakes

47.4

Finally, the last valve to be identified in a typical combination valve is the metering valve (Labeled as “A” in Figure 47.3). You can locate the metering valve between the master cylinder and front brakes. The majority of RWD vehicles have disc brakes on the front, while drum brakes on the rear have a metering valve. As a result, you should look for the presence of a stem. For example, the stem may protrude from the rubber cap located at the end of the valve, or the rubber cap may cover it up.

The metering valve’s function is to hold off the front brake application until the rear brakes overcome the return springs. The valve does this to allow all brakes to apply at the same time. The combination valve pictured in Figure 47.4 doesn’t have a metering valve. The valve only serves as a junction block for the front brake lines and a proportioning valve.

The next category of brake valves to look at are those combination valves used on FWD vehicles. The majority of brake valves used on FWD vehicles will be dual proportioning valves combined into a standard housing, as shown in Figure 47.5. Each rear brake on a diagonal split hydraulic system is on a separate circuit. Because of the separation, FWD vehicles have two proportioning valves.

Combining the two proportioning valves into standard housing is the most frequently used method. Older FWD vehicles may also include the pressure differential switch in the combination valve, as shown in Figure 47.6. Newer FWD vehicles use a fluid level switch in the master cylinder reservoir instead of the pressure differential switch.

Proportioning Valves

47.5

Pressure Differential Switch

47.6

FWD Combination Brake Valve

An important point to understand about FWD combination valves is that although the lines from the front wheels connect to the valve, fluid flow is unrestricted through the valve. The valve serves only to accomplish the diagonal split “plumbing” but does not act on the fluid flow to the front brakes. FWD vehicles don’t have metering valves or any valve that would limit front braking. The reason for this is due the front brakes do most of the work.

While the majority of FWD vehicles combine the proportioning valves into a familiar housing, others do not. For example, Figures 47.7 & 47.8 show two alternate methods of equipping an FWD vehicle with two proportioning valves. Figure 47.7 shows screw-in proportioning valves used on some four outlet master cylinders, while Figure 47.8 shows side-by-side proportioning valves used on some other FWD vehicles. Some FWD vehicles build the proportioning valves into the master cylinder, as shown in Figure 47.9.

47.7

47.7

47.8

47.8

47.9

47.9

Height Sensitive Brake Valve

The proportioning valves pictured in the previous Figures are hydraulic activated valves. Likewise, they rely on system pressure to know when to operate. However, there is another category of proportioning valve that depends on vehicle ride height to function. Typically, we call these valves height-sensitive control valves, load sensing proportioning valves, or “smart” valves (See page 88 for more detail). The identifying characteristic is the presence of linkage between the valve and the vehicle’s suspension.

For example, there are two typical height-sensitive control valves shown in Figure 47.10. The top valve is from a car equipped with a front to rear split hydraulic system. The bottom valve is from a vehicle equipped with a diagonal split hydraulic system. This valve is a type of combination valve because it houses two separate valves in the same housing.

4.10

47.10

Conventional brake valving may be attached or incorporated into the ABS. The ABS modulator shown in Figure 47.11 has the combination valve attached directly to it. They appear as one unit but are two separate parts. Some ABS systems use screw-in proportioning valves similar to those used in some master cylinders.

Some newer vehicles will not have any mechanical brake valves. Because advances in computer technology have allowed the ABS computer to take over the job of the proportioning valve. These systems let the rear brakes operate up to the point of wheel lock-up and then use micro-pulses to control the pressure to avoid the lock-up. The mico-pulses do not produce the traditional ratcheting pedal drop as experienced during a usual ABS stop. They have tiny and very rapid changes in pressure, which in many cases is unnoticeable in the pedal.

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How to Determine Intermittent Low Brake Pedal on Vehicles equipped with Delco VI ABS

How to Determine Intermittent Low Brake Pedal on Vehicles equipped with Delco VI ABS

Delco VI ABS

Problem: Intermittent low brake pedal on vehicles equipped with Delco VI ABS (see figure 46.1) 

Cause: EMB (electromagnetic brake) or ESB (expansion spring brake) not holding the motor in homed position. See more info section.

Solution: This condition is usually not straightforward to diagnose. The primary reason for this is its intermittent nature. The most effective method of diagnosing it will be to look for supporting symptoms of the condition. The symptoms that will support the EMB or ESB as the cause of the low pedal will be:

  1. ABS light on with either a code 38 (left front), code 41 (right front), or a code 42 (rear brake circuit).
  2. The problem occurs only ONCE per drive cycle.
  3. The occurrence of the issue should be in time with the ABS light coming on.
  4. There should be an underhood noise associated with the event as the piston causes the gears to the wind.

You can also diagnose it by looking for the symptoms that don’t support the EMB or ESB brakes as being the cause but do support the master cylinder as the cause: 

  1. If you can duplicate the problem with each pump of the brake pedal or more than once without resetting the ABS, the problem is the master cylinder.
  2. If the problem occurs without a code, noise from the modulator/ motor pack, the problem is the master cylinder.
Delco VI motor Driven Pistons
Figure 46.2

More Info

ABS failures rarely cause conventional brake problems, but it is wise to be aware of those that can. The lack of this knowledge can lead to many hours of wasted effort and frustration. While most technicians are familiar with the RWAL/RABS dump valve causing excessive pedal travel, few are aware of a similar problem with the Delco VI. The Delco VI is the most common ABS in use today based on the number of units in the field. It is also unique in how it modulates the brake pressure during an ABS stop. Instead of solenoid sets and a pump motor assembly, the Delco VI uses motor-driven pistons (Figure 46.2).

The pistons are driven up and down by high-speed bidirectional motors to modulate the brake pressure during an ABS stop. During standard braking, the pistons are held in their uppermost or “homed” position by two types of motor brake assemblies. The motor brakes prevent the pressure in the system from pushing the pistons down during standard braking.

Delco VI Expansion Spring Brake
Figure 46.3

The most common type of motor brake is known as the expansion spring brake. As shown in Figure 46.3., this type is located at the base of the motor. The expansion spring prevents the large gear on the base of the piston/worm gear assembly from spinning the small motor gear but allows the motor to drive the small gear in either direction.

Delco VI electromagnetic motor brake

Electromagnetic Motors

Some Delco VI units utilize an electromagnetic motor brake, as shown in Figure 46.4. This design uses three small brake pads in a tripod holder:

  • The holder is attached to the top of the motor shaft.
  • Brake pads clamped between a base plate.
  • And a spring-loaded upper plate. 

This clamping prevents the motor from spinning during standard braking. The system charges an electromagnet during an ABS stop, pulling the top clamping plate up and releasing the tripod assembly. The electromagnet will stay energized during the ABS cycle allowing the motor to drive the piston up and down to regulate pressure.

If any of the three motor brakes fail, it will not maintain the piston in its homed position. The pressure generated from standard braking will drive the piston down in its bore, as shown in Figure 46.5. The extra fluid volume needed to fill this space will cause the brake pedal to travel to the floor, acting as a master cylinder problem.

There will be some noticeable differences when this failure occurs when compared to a bypassing cup seal. The first thing that should happen is the ABS light should come on. The Delco VI will trigger a code 38 for the left front motor brake, code 41 for the right front, and code 42 for the rear. The second thing that you should notice is the problem will happen only once per drive cycle. Once the piston is in the down position and the code has been triggered, the ABS shuts down. The brakes will be regular until the process of the ignition begins again and the vehicle self-tests. When this occurs, the EBCM will drive the pistons to their homed position.

Looking for Symptoms

Newer systems will self-test without driving the vehicle, while older ones require a test drive above four mph. Once the self-test occurs, the problem can reoccur. One last thing that will help differentiate this problem from that of a failed master cylinder. The Delco VI is a loud system when it operates. If a motor brake fails and the pressure pushes down the piston, it will produce a pronounced noise from the modulator/ motor pack assembly. You will hear the piston and motor gear winding. In class, I hot wire the EMB and duplicate this problem to demonstrate it to the students. You can’t miss it. So before you perform some of the involved procedures published, look for these symptoms. Assuming the line lock test is pointing you to the master cylinder/modulator, then in

basic terms:

  • If you can duplicate the problem with each pump of the brake pedal or more than once without resetting the ABS, the problem is the master cylinder.
  • If the problem occurs without a code, noise from the modulator/ motor pack, the problem is the master cylinder.

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Low pedal on vehicles equipped with Kelsey Hayes EBC310/EBC325/ EBC410 ABS systems

Low pedal on vehicles equipped with Kelsey Hayes EBC310/EBC325/ EBC410 ABS systems

foot on pedal

Bypassing dump valve in modulator allowing fluid into the low-pressure accumulator causes low pedal on vehicles equipped with Kelsey Hayes EBC310/EBC325/EBC410 ABS systems. The EBC310/EBC325 system is on GM, Ford, and some Dodge light trucks and SUVs. The EBC410 system is on the Ford Windstar. There are slight differences in the external look of the units, as shown in Figures 45.1 and 45.2. The main difference we are concerned with for the dump valve diagnosis is the number of rubber caps. The modulators in question can be equipped with 2, 3, or 4 rubber caps, as shown in Figures 45.1, 45.2, and 45.3. Understanding where the low-pressure accumulators are is key to accurate testing. The rubber caps marked with arrows are the low-pressure accumulators. To perform the dump valve diagnosis, follow the steps below:

45.1

Figure 45.1

45.2

Figure 45.2

45.3

Figure 45.3

Add Your Heading Text Here

1. Locate the low-pressure accumulator caps. You find them on the brake line end of the modulator. Remove either of the rubber caps covering the cap vent.

2. Insert a straightened paper clip into the cap screw vent hole until it bottoms out.


3. Have someone start the vehicle and apply the brakes while slowly increasing brake pedal pressure. NOTE: Be sure to duplicate the fade for the test to be accurate.


4. If the paper clip pushes out, the dump valve bypasses, you’ll need to replace the modulator. If the paper clip does not move, perform steps 2 and 3 on the other low-pressure accumulator.

Intermittent Diagnosis:

46.1

When it comes to intermittent low brake pedals on vehicles equipped with Delco VI ABS (See Figure 46.1), the low brake comes from EMB (Electromagnetic brake) or ESB (Expansion spring brake) not holding the motor in homed position.

Solution: This condition is usually not straightforward to diagnose. The primary reason for this is its intermittent nature. The most effective method of diagnosing it will be to look for supporting symptoms of the condition. The symptoms that will support the EMB or ESB as the cause of the low pedal will be:

1. ABS light on with either a code 38 (left front), code 41 (right front), or a code 42 (rear brake circuit).

2. Problem occurs only ONCE per drive cycle.

3. The occurrence of the problem should be timed with the ABS light coming on.

4. There should be an underhood noise associated with the occurrence as the piston causes the gears to the wind. 

You can also diagnose it by looking for the symptoms that don’t support the EMB or ESB brakes as being the cause but do support the master cylinder as the cause:

1. If you can duplicate the problem with each pump of the brake pedal or more than once without resetting the ABS, the problem is the master cylinder.

2. If the problem occurs without a code, noise from the modulator/motor pack, the problem is the master cylinder.

46.2

Figure 46.2

More Info

ABS failures rarely cause conventional brake problems, but it is wise to be aware of those that can. The lack of this knowledge can lead to many hours of wasted effort and frustration. While most technicians are familiar with the RWAL/RABS dump valve causing excessive pedal travel, few are aware of a similar problem with the Delco VI. The Delco VI is the most common ABS in use today based on the number of units in the field. It is also unique in how it modulates the brake pressure during an ABS stop.

Instead of solenoid sets and a pump motor assembly, the Delco VI uses motor-driven pistons (Figure 46.2). The pistons are driven up and down by high-speed bidirectional motors to modulate the brake pressure during an ABS stop. During standard braking, the pistons are held in their uppermost or “homed” position by two types of motor brake assemblies. The motor brakes prevent the pressure in the system from pushing the pistons down during standard braking.

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Diagnosing Excessive Pedal Travel on Rear Wheel ABS Vehicles – RWAL & RABS

Diagnosing Excessive Pedal Travel on Rear Wheel ABS Vehicles – RWAL & RABS

Problem: Low Brake Pedal

Bypassing dump valve in modulator allows fluid into the low-pressure accumulator causing low brake pedal on vehicles equipped with RWAL or RABS ABS systems.

Low Brake Pedal Solution

Whenever an RWAL/RABS equipped vehicle presents itself with a low brake pedal, the first thing that you should check for is a bypassing dump valve. The method of testing depends on the style of the valve. These vehicles use two different design modulators.


The steps used in the diagnosis of the dump valve will depend on the modulator design. The first step is to locate the modulator and determine its type. Then use the following information to diagnose it. (Note: The “Type” designations are assigned by me for reference in this article and are not Kelsey Hayes designations)

Type 1: Rear Wheel ABS "Torpedo Style"

This valve is one of 2 designs used on vehicles equipped with rear-wheel ABS. It is identified by its cylindrical shape, as shown in Figure 44.1. To perform the dump valve diagnosis, follow the steps below

1. Remove the 1-1/4” cap screw at the end of the valve body as well as the low-pressure accumulator spring.

2. Insert a screwdriver or similar tool into the backside of the low-pressure accumulator piston. (See images below)

3. Have someone start the vehicle and apply the brakes while slowly increasing brake pedal pressure. 

NOTE: The brake pedal fade must be duplicated for the test to be accurate. 

4. If the low-pressure accumulator piston pushes against the screwdriver, the dump valve bypasses, and you will have to replace the modulator.

Example 1
Example 2
Schematic

Type 2: Rear Wheel ABS "Block Style"

Block style is the other valve used on light trucks equipped with rear-wheel ABS. It is identified by its block-shaped body, as shown below. To perform the dump valve diagnosis, follow the steps below:

1. Locate the low-pressure accumulator cap and remove the rubber cap covering the cap vent.

2. Insert a straightened paper clip into the cap screw vent hole until it bottoms out, as shown below.

3. Have someone start the vehicle and apply the brakes while slowly increasing brake pedal pressure. 

NOTE: The brake pedal fade must be duplicated for the test to be accurate.

4. If the paper clip pushes out, the dump valve bypasses, and you will have to replace the modulator.

RWAL/RABS Valve
Block Style
Schematic

Confirming Low Brake Pedal Diagnosis

If the above steps indicate a bypassing dump valve, you will need to replace the modulator. However, before installing the modulator, you should check the system for additional causes of excessive pedal travel. The most effective method to accomplish this is to temporarily “fix” the modulator. Doing so can be achieved by following the steps below.

Confirmation on RABS/RAWL System

1. Remove the cap screw and low-pressure accumulator spring.
2. Insert a solid spacer in place of the spring to prevent the low-pressure accumulator piston from moving. Install the cap screw. (See Figure 44.7).
3. Start the vehicle and check the brake pedal. If the pedal feel is now correct, all that is necessary is to complete modulator replacement. If the pedal is better but still low, perform a line lock test to determine the cause of additional pedal travel.

NOTE: You should use spacers as a diagnostic technique only. You should never leave them in place.

Intermittent Diagnosis - Low Brake Pedal

Dump valve failure can occur on an intermittent basis making a diagnosis in the shop difficult to impossible. If the failure is intermittent and can only duplicate it on a road test, use the steps below. There are two designations to simplify the diagnosis.

Vented Cap Screw Design (Rear Wheel ABS "Block Style")

1. Insert the straightened paper clip through the rubber vent cap as shown below until it bottoms out.
2. Use a magic marker or piece of tape to mark the position of the paper clip relative to the rubber cap, as shown below.
3. Test drive the vehicle until you can duplicate the pedal fade.
4. Check the position of the paper clip. If the paperclip falls out, dump valve failure has occurred, and the modulator requires replacement (See Image Below). On the other hand, if no movement has taken place, the source of the pedal fade is not ABS-related.

3.1
3.2
3.3

NOTE: It is crucial not to engage the ABS during this test. Low-pressure accumulator movement occurs during the ABS cycle.

Non-Vented Cap Screws (Torpedo Style Rear Wheel ABS)

1. Remove the cap screw and low-pressure accumulator spring. Note the piston position. Reinstall the cap screw.

2. Test drive vehicle until you duplicate the pedal fade.

3. Remove cap screw and check low-pressure accumulator position. If the piston is against the cap screw, dump valve failure has occurred, and the modulator you will have to replace the modulator

NOTE: it is vital not to engage the ABS during this test. Low-pressure accumulator movement occurs during the ABS cycle.

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Determining Cause of Low Brake Pedal – Line Lock Test

Determining Cause of Low Brake Pedal – Line Lock Test

When it comes to low brake pedals, there are many possible causes. As an example, the list below shows the most common causes for low brake pedal:

  • Air in the hydraulic system
  • Rear brake adjustment
  • Fluid leak (pressure)
  • Internal bypass (i.e., RWAL/RABS dump valve bypass)
  • Seized slider mechanism
  • Excessive clearance between brake pads and the rotor
  • Binding or cocked brake pads
  • Self-adjustment in the calipers is not taking place as designed

Although this list is not all-inclusive, it does represents the most common causes. Likewise, it demonstrates why you should use a systematic approach when diagnosing a low brake pedal complaint.

Low Brake Pedal - Solution

2 Line locks

Systematically approaching the problem will enable you to pinpoint what part of the system is responsible for the extra pedal travel. As you use this method, you will begin to focus your attention on one area rather than taking a random or shotgun approach to the problem. The most effective way to start the process is with what is known as a line lock test. A line lock (pictured above) is a device that allows you to pinch a brake hose off without damaging it. Installing line locks will let you break a rather complex system down into smaller parts.

On rear-wheel-drive vehicles equipped with a front to rear split hydraulic system, installing 3 line locks will break the plan down into four parts, each front wheel, the rear axle circuit, and from the line locks up to the master cylinder see below. Four line locks installed on a front-wheel-drive diagonal split system will break the brake system into five parts (Second image below). Each wheel and the rest of the system. To perform the line lock test, follow the steps below:

Front wheel drive schematic

Line-Lock Steps to Fix Low Brake Pedal

1. Inspection

Perform a visual inspection for pressure leaks that would cause the pedal problem. If you can’t find any apparent cause, proceed to the next step. On the other hand, if you find a problem, correct it before moving on.

2. Install Line Lock

Install a line lock on each brake hose in the system (on multiple hose arrangements, only one line lock is necessary). Position each line lock about midway down the hose.

3. Test Line Lock

With the wheels off the ground, vehicle in neutral, have someone start the car and apply the brake pedal. Attempt to turn each wheel. If you installed the line locks correctly, the wheels should spin. If one or more wheels do NOT spin, the line lock has not held pressure. Go to step. If all wheels spin, go to step 5.

4. Adjust Line Locks (if necessary)

Release the brake pedal. Remove the line lock(s) on the wheel(s) ) that do not spin. Reinstall the line lock(s), making sure the locks are tight. Repeat step 3 until all wheels spin.

5. Testing the Pedal

Making sure the vehicle is running, apply and hold the brake pedal. If the brake pedal is rock hard after taking the free play out of the linkage, go to step 7. If the pedal is spongy or has excessive travel before it gets hard, go to step 6.

Note: With the line locks installed, the pedal should no longer be able to move. The regular movement of the brake pedal causes the movement of the caliper & wheel cylinder pistons. After installing line locks, there is nowhere for the fluid to go, so the brake pedal should be rock hard.

6.Spongy Brakes

If you’ve installed line locks and the brakes feel spongy, there is a problem in front of the line locks. The most common cause of this is air in one or more of the components. For vehicles equipped with the Kelsey Hayes rear-wheel or four-wheel ABS systems, the reason for the pedal travel could be a bypassing dump valve.

7. Below the Lock Lines

If the pedal is hard after installing the line locks, the hydraulic system is in good condition and functioning correctly from the line locks up. Excessive pedal travel comes from problems at one or more of the wheels. With the vehicle running and the brake applied, have someone remove the rear line lock if the car is a rear-wheel-drive or the right rear line lock if the vehicle is a front-wheel-drive.

Next, note the amount of pedal drop. When adding a drum brake axle back into the system, the expected pedal drop should be ¼” to ½” if adequately adjusted and no air is in the system. When adding one drum brake back into the system, the drop should be 1/8” to ¼.” If the pedal drop is more than expected, go to step 8. If the pedal drop is correct, go to step 9.

8. Pedal Travel

The most common cause of excessive pedal travel on drum brake systems comes from a lack of self-adjustment. The only other reason could be air from the line-lock down to the wheel cylinder. Either fix the cause now or reinstall the line lock and continue with the next step. When reinstalling the line lock, make sure the wheel has is isolated before continuing.

9. Check Pedal Drop (FWD vehicle only)

On RWD vehicles, proceed to the next step. On FWD vehicles, remove the left rear line lock and note pedal drop. If excessive, go to step 8.

10. Check Pedal Drop

With the vehicle running and brake applied, remove the right front line lock and note the amount of pedal drop. A typical disc brake should drop ¼” to ½.” Go to the next step if the pedal drops more than this amount. If the pedal drop is ordinary, go to step 12.

11. Pedal Drop After Adding Disc Brake

If you have excessive pedal drop when adding a disc brake back in the system. Check for the following:

  • Seized slider mechanism
  • Excessive clearance between brake pads and rotor
  • binding or cocked brake pads
  • Air at one or both front calipers
  • Self-adjustment in the calipers is not taking placed as designed
  • The vehicle has a QTU master cylinder and QTU valve is bypassing

12. Standard Pedal Drop

If you have a standard pedal drop after adding the right front wheel back into the system, repeat step 10 with the left front wheel.

The line lock is one of the most effective diagnostic tools a technician can have in their boxes and no technician should be without them.

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Reading Brake Pedals

Reading Brake Pedals

Not correctly “reading” brake pedals can lead to you wasting time. All too often, mechanics spend time trying to restore pedal height when no problem exists. Likewise, not learning how to read the brake pedal can lead to a vehicle delivery with a less-than-perfect pedal.

How to Read Brake Pedals

“Reading” brake pedals is the process of determining the height and feel of the brake pedals. In fact, pedal “reading” is an essential diagnostic step, and it is important to complete it correctly to perform an accurate diagnosis. As a result, you can return a customer’s car with a little extra confidence.

Brake Pedals - Height Adjustment

1. With the vehicle off, pump the brake pedal to deplete the vacuum in the
booster. As a result, the pedal should become very firm.

2. With your foot on the brake pedal and applying the same pressure as you would if you were usually starting a car, start the engine while noting the amount of pedal drop. If necessary, use a tape measure to accurately measure the amount of depth. For example, see Figure 40.1.

3. Figure 40.2 shows the same pedal with more pressure applying to it. Notice the pedal is now traveling 2.5” more. This measurement is typical and should not be considered a problem in the system on most vehicles.

4. When determining the condition of a brake pedal, check the pedal height with the vehicle in gear, and the brake applied just the point where it prevents the car from moving.

5. Next, test-drive the vehicle and make several stops applying light, moderate, and, if necessary, panic braking pedal forces.

NOTE: Never test drive a vehicle with an unsafe brake pedal.

6. Another good technique is to compare the brake pedal to another vehicle of the same make and model. It is essential to understand that there are wide variations on brake pedal feel and height between cars. Each car has to be assessed based on its characteristics and compared to similar vehicles. 

Figure 40.2

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Caliper Mounting Bolts

Caliper Mounting Bolts

Most caliper mounting bolts and bracket bolts do not require special steps or torquing procedures to install. Typically, most caliper mounting bolts will be between 15 and 50ft. lbs. Thought that is true for many bolts, there are, in fact, other bolts that will require a process to correctly tighten.

Some mounting bolts require specific steps when tightening. Failure to follow these steps can cause the bolts to come loose. As a result, wheel damage and potential safety problems can occur if the caliper locks the wheel up.

The best possible practice is to follow the torque specifications whenever tightening mounting bolts. In the real world, this is not possible. Here are some guidelines when working with caliper mounting bolts:

Caliper Mounting Bolt Tightening Steps

  • Check the mounting bolt threads for signs of Loctite. (See Figure 39.1) If threads show signs of Loctite, the threads should be cleaned, and a new Loctite should be applied. Torque the bolts to the manufacturer’s specifications.
Bolts with Loctite

NOTE: Some manufacturers state bolt replacement is necessary.

  • The larger the mounting bolt, the higher the required torque. Some of these bolts, such as those pictured in Figure 39.2, need tightening torques over 100 ft. lbs. On larger mounting bolts, you must tighten the bolts correctly.
39.2

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Removing Broken Bleeder Screws

Removing Broken Bleeder Screws

Every good technician has to bail themselves or someone else out of a jam once in a while. For example, in brake service, you may have to deal with a broken bleeder screw. Typically, if a vehicle comes in with a fractured bleeder, you’d include the price of the caliper on the estimate. On the other hand, what do you do when one of your techs walks finds a broken bleeder screw? Likewise, what if a replacement caliper is not readily available, or you don’t want to take the cost of fixing it? What now?

Enter the old bag of tricks. Even though many techs have tried to perform the task of removing a broken bleeder, most do not have a great deal of success. Furthermore, mechanics have used all manner of methods to remove bleeder screws. Whether it be drilling, tapping, easy outs, heat, or even a combination of these, mechanics have tried it all. On the other hand, there is one method in particular that will work virtually every time. And the best part? It’s not that difficult to perform.

Removing a Broken Bleeder Screw

First, the process will involve disassembling the caliper. Because of this, you should use a rebuild kit when available. If one is unavailable, then take great care when removing the dust boot and square-cut seal. Next, after stripping down the casting, mount it in a vise. Next, using a hacksaw, cut a screw slot in the top of the broken bleeder as in the image below. If the bleeder is flush with the housing, you will have to cut into the housing a small amount. This portion of the casting is a non-structural part, and if done correctly, this will not harm the caliper.

Flush bleeder Screw

Heating the Bleeder Screw

Next, get a container big enough to fit the entire caliper housing and fill it with enough water to allow the caliper to be completely submerged. For instance, a mop bucket or 5-gallon pail works nicely. Now apply heat to the caliper housing around the bleeder screw as in the image below.

Heating the bleeder screw

Once heated, grab the caliper with a pair of channel locks, remove it from the vise and set it in the bucket of water. Let the caliper sit there for a minute and then remove it and remount in the vise. Next, using a flat blade screwdriver that fits snug in the screw slot, attempt to remove the bleeder. It may be necessary to tap the screwdriver tip into the screw slot with a hammer to ensure a good fit. In most cases, the bleeder will come out without any problem (See Image Below). Occasionally there will be a burr on the threads, and you will have to work the bleeder back and forth until it comes out.

Empty bleeder screw socket

This process will “shock” the caliper housing serving to break the bond between the two parts. Many mechanics have used this method for years, and it has yet to fail. However, on a rare occasion, you’ll have to heat it twice before the bond breaks. Likewise, you can also use this method on wheel cylinders. However, there are a few things to be careful of:

  • Never attempt this on an aluminum caliper or wheel cylinder.
  • Be sure to disassemble the wheel cylinder before heating it because heat can damage the internal rubber parts.
  • Once you complete the job, always check the unit for leaks.

After Removing the Broken Bleeder Screw

After removing the bleeder, you’re ready to reassemble the caliper. Start by cleaning the bore out with emery cloth if necessary, and rinse with hot water. Next, blow the housing dry with compressed air. As you begin the assembly process, it is essential to make sure your hands are clean. When installing the square-cut seal, piston, and dust boot, use either brake fluid or silicone as an assembly lube. Install the piston by hand, making sure not to cock it. If the unit uses a press-in dust boot, make sure to seat it completely. Complete the process by installing the slider hardware making sure to lube it properly. Finally, install the caliper and bleed it out, making sure to check for leaks.

Tip box - "A good technician always has a number of tricks up their sleeves to bail themselves out of problems an this technique should be one of them."

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Opening Seized Bleeder Screws

Opening Seized Bleeder Screws

Every now and then, you might run into a stuck bleeder screw. This can be frustrating, especially because bleeder screws are supposed to be a simple step in the process.This article aims to help you know what to do whenever one gets stuck. Likewise, it goes over a few different solutions as each situation may differ.

Bleeder Screws Not Opening

The effort required to open bleeder screws will vary from on vehicle to another. The factors that effect this are:

  • Age of the vehicle
  • Operating environment
  • Rubber cap equipped
  • Whether they have ever been opened

Solution

NOTE: When attempting to open a bleeder screw always use a six point socket or wrench. Use of a 12 point socket or wrench will increase the chances for rounding the bleeder screw and increase the difficulty in removing it. Follow these steps to open the bleeder screw:

 
First, remove rubber dust cap if equipped. Using correct size wrench or socket, apply mild force to see if bleeder will open easily. If bleeder will not open stop attempting to open it without following the procedures below. Continuing to force it to open may result in breaking it

Bleeder Screws Method 1:

1. Use a hammer to tap on the head of the bleeder screw. Mushrooming the bleeder screw head is acceptable as long as the wrench or socket will still fit on (See Below).
 
2. Tap on the caliper housing all around the bleeder screw. After doing these steps try the bleeder again.
 
3. If necessary repeat steps 1 and 2 above. If bleeder still will not open you will have to use Method 2 listed below.
Bleeder Screw

Method 2:

Using the tool shown in the image below and the appropriate size socket apply vibration to the bleeder screw while working the handle back and forth with even pressure. Do not force the bleeder screw. Keep applying the vibration until the bleeder screw opens. If the bleeder screw still will not open the caliper or wheel cylinder will have to be rebuilt or replaced
Tool

Any further trouble? Phoenix systems has developed an easy to use method that vibrates the bleeder screw while working it back and forth with a 3/4″ wrench. Click the button below for more information and a short video on how to use our BrakeFree product.

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GM W Body Rear Caliper Inspection Tips

GM W Body Rear Caliper Inspection Tips

Irregular pad wear, low brake pedals, and brake fluid leaks are all potential problems when it comes to front brake pad wear. This article will go over the causes and solutions to premature front pad wear and how to perform a caliper inspection.

Caliper Inspection Tips

The design of the caliper is such that it can suffer any number of failures. The symptom caused will depend on the type of failure. Here is a break-down:

  • Seized sliders – symptoms: irregular pad wear on rear, premature front pad wear and lack of stopping power and possibly low pedal
  • Lack of adjustment – symptoms: low brake pedal and premature front pad wear
  • Piston cup seal leaking – symptom: fluid leak seepage from piston vent and possibly friction contamination from brake fluid

Solution

A thorough inspection of the rear dis calipers will determine if they are functioning as designed. Follow the steps below:

1. When possible, apply the parking brake and check if either of the rear wheels will rotate. When one or more parking brake cables prevent this from being done, use a pair of channel locks to apply each caliper’s parking brake. In the case of either rotor being able to rotate with the parking brake applied then self adjustment has not been taking place. If both parking brakes are working properly go to step 3. If not, proceed to next step.
 
2. One or both wheels spin with parking brake applied – if the parking brake system works pump parking brake several times while holding the release lever. This should self adjust the rear calipers. If parking brake system is not functioning, apply and release each caliper’s parking brake lever several times using a pair of channel locks. Recheck parking brake function. If parking brake now holds the wheels go to next step. If one or both wheels still rotate with parking brake applied caliper replacement is necessary. It is advisable to replace calipers in pairs.
 
3. Parking brake holds properly. Remove calipers and check slide pins for free movement. If any of the slide pins are seized calipers should be replaced (See Figure 36.1). If any of the slide pins are sticking slider service should be performed or the option of caliper replacement offered to the customer. When all the pins move freely they should be lubed as part of the service. Go to next step.
Caliper

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Effective Slider Service – Fighting the Elements

Effective Slider Service – Fighting the Elements

When moisture finds its way into a caliper housing, corrosion begins to cause premature pad wear. This article goes over the process of performing an effective slider service in order to fix the issue. Below, you will find pictures along with a step by step guide to complete the process correctly.

Before the Slider Service

Often times, calipers like the one below are given a quick glance and dubbed to be in good condition. In other words, if the dust boot is in one piece and the slider spin moves, then everything is ok. However, this is not the case. In truth, the caliper pictured below could have a number of conditions that would require a service. In addition to inspecting the part, it is important to consider other conditions that might have caused the vehicle to come back prematurely. In this example, the following results were found upon closer inspection:

Caliper

Slider Pins

As pictured in image 35.2, one of the slider pins had a portion of the anodized coating worn off. (For those that don’t know, the anodized coating is important because it prevents corrosion.) As a result, the worn portion is now susceptible to corroding. In this case, industry accepted guidelines suggest that the pin should be replaced.

Slider Pin
Corroded slider pin

On the other hand, image 35.3 had not only lost it’s anodized coating, but had already begun to corrode as well. Much like a healthy pin, this part still moved as normal.

Caliper Housings

Floating caliper housings utilize casting holes to house the rubber bushings, o-rings or boots. In fact, Moisture intrusion into the caliper housing casting holes results in corrosion in many types of floating calipers.Likewise, as the casting holes corrode the inner diameter of the casting hole is reduced which leads to the rubber bushing, o-ring or boot to be squeezed around the mounting pin. This squeezing results in the caliper housing’s movement being restricted.

Corrosion of caliper housing
Image 35.5

Now that we know the conditions that can occur because of moisture intrusion lets discuss how to prevent it or at least slow it down. First, a good dust boot does not mean moisture can‘t effect the pins as shown in Figures 34.2 & 34.3. Both of the dust boots on these pins were intact. Likewise the corroding of the caliper housing where the slider parts reside can‘t be stopped with a good dust boot. The key to preventing these types of problems is in forming moisture barriers. Follow the steps below to form moisture barriers on floating calipers:

Slider Service Steps

1. First, remove all caliper hardware from housing.

2. Second, clean the caliper casting housing holes. When flaking rust has formed tools such as a ball stone hone, wire brush or wheel cylinder hone will not be effective in removing this type of rust. Flaky rust such as that shown in Figure 34.4 will have to be either ground out using a dremel tool or blasted out using an abrasive blaster. The cleaning process should remove the rust but not good material. The end result should look similar to Figure 34.6

3. Third, use a high quality silicone lubricant to place a film in each casting hole as shown in Figure 34.7.

Caliper housing
35.7

Adding Silicone

4. Coat the portion of the rubber boot that seats against the casting hole with silicone. Using the brush place a light coat of silicone on the inside of the rubber boot making sure to lube the sealing ridges on each end of the boot. See Figures 34.8 & 35.9.

Rubber boot

5. Install the rubber boots into each of the casting holes. The silicone on the casting hole should mix with the silicone on the boot to form a protective layer as shown in Figure 35.10. Note: More is not better. Too much lube can cause more problems than it cures. The silicone in the casting hole combines with the silicone on the rubber boot to form an effective moisture barrier.

6. Place a layer of silicone lubricant on the sealing ridge of each pin as shown in Figure 34.11.

silicone protective layer
Sealing ridge

7. Install each pin in its rubber boot. The silicone on the sealing lip of the boot will mix with the silicone on the sealing ridge of the pin to form a protective layer (See Figure 35.12)

Caliper replaced

The steps above cover the process when servicing boot style floating calipers. The steps would be similar when servicing bushing and o-ring style calipers.

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Caliper Replacement Guidelines

Caliper Replacement Guidelines

There are so many variables that effect the operation of a caliper, it is impossible to place a generic lifespan on them. Because of this, a good mechanic will develop the ability to be able to accurately determine when it is time to replace the calipers. For your example, this article will go over the signs of wear as well as the different options of calipers out there.

Determining Caliper Replacement

Replacing calipers with every brake job would be considered overselling by most customers and regulators. On the other hand, never replacing calipers would be considered underselling by most shops. Typically, there are two groups of customers who should be offered the option of replacing the calipers. To emphasize, notice the word “option”, meaning the customer will have a choice.

Group 1: If the vehicle fits the following criteria the customer should be offered the option of replacing the calipers:

• The vehicle has high mileage
• Original equipment calipers are still installed
• Each set of pads lasts less than the previous set (premature pad wear)

Presenting Caliper Options

When presenting the option of replacing the calipers you should make the following points:

• First, explain to the customer that based on the vehicle’s history and current condition the only way to restore maximum pad life is to service the inside of the caliper. This usually means replacement. As a result, the function of the square cut seal will be restored. (See more info below for a better explanation of the square cut seal).

Group 2: When a vehicle fits the following criteria, the customer should be offered the option of replacing the calipers:

• Start by informing the customer that parts or labor will be required to restore the caliper’s. However, If the caliper requires the replacement of smaller parts, the customer should also be given the option of replacing the caliper (See Figures 34.1). Often times it can actually end up being more expensive to fix the caliper than to replace it.

Various calipers with different levels of wear

Note: Without a proper inspection most of the conditions listed above would NOT be found. 

More Info: Floating Caliper Operation

Calipers are not “instant on, instant off” parts. This is because they go through a cycle or process during both the “apply” and “release” phases. (See Figure 34.3).

Brake Illustration

Unapplied

Understanding these 2 processes is key to being able to identify many of the causes of premature pad wear. To begin, the “apply-cycle” starts with the application of the brake pedal, which results in pressure being generated in the hydraulic system. Likewise, hydraulic pressure created in the caliper housing pushes in all directions. In fact, the operation of the caliper works on the principle that things will take the path of least resistance. The easiest thing to move in a floating caliper should be the piston. Hydraulic pressure pushes the caliper piston into the inboard brake pad causing it to press against the inner friction surface of the rotor (See Figure 34.4).

Inboard pad illustration

Inboard Pad

Once the inboard pad is against the rotor, the caliper piston is no longer the easiest thing to move and system, causing pressure increase. Next, the easiest thing to move is the caliper housing. As a result, pressure acts against the caliper housing using the caliper piston as a backstop. This pressure causes the caliper housing to move toward the center of the vehicle on its mounting pins. Inward movement of the caliper housing pulls the outboard pad against the outer friction surface of the rotor (See Figure 34.5). Once both the inboard and outboard brake pads are against the rotor’s friction surfaces, increasing the hydraulic pressure results in even clamping of both brake pads.

Outboard pad illustration

Release Cycle

A different process takes place to allow the brake pads to release. For example, the part responsible for the release of the brake pads is the square cut seal. The square cut seal is a square o-ring that sits in a machined groove in the caliper housing. You’ll notices that the groove in the caliper housing is beveled towards the open end of the bore. This square cut seal forms a seal between the caliper housing and the piston’s sealing surface (See Figure 34.6).

Sealing surface

As the caliper piston moves out to apply, the square cut seal is flexed into the beveled portion of the housing groove. Next, the square cut seal will remain in the stretched position as long as the brake pedal is applied (See Figure 34.7).

Square cut seal

Finally, once the brake pedal is released and system pressure goes to zero, the square cut seal returns to its natural relaxed state because of its elastic properties. As the square cut seal returns to its natural state it pulls the caliper piston back with it. The relaxing of the square cut seal is what is responsible for the release of the disc brake pads.

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Wheel Tightening Procedures

Wheel Tightening Procedures

When a wheel is installed incorrectly it can cause disc thickness variation in the rotors. As a result, the vehicle starts to experience pulses when braking. In contrast, when wheels are tightened correctly, the vehicle should maintain its proper condition. In order to prevent reoccurring pulsation complaints, this article will show you the correct procedure for installing and tightening wheels.

Installing a Wheel

The process of installing a wheel is very simple and only involves two key steps. When both steps are done properly whell induced runout will be elinated as a potential problem. For example, the steps are listed below:

1. First, tighten the wheel using the correct sequence. (More on that below)

2. Second, use a process called “step torquing”.

Wheel Tightening Procedures

By tightening the wheels lugs in the correct fashion promotes both safety and proper brake operation. In order to preform the installation correctly, all wheels should be tightened and torqued in the same process:

1. Hand tighten all lug nuts using a star pattern.

2. Next, tighten all lug nuts to approximately 1/2 specification using the same star pattern.

3. Tighten all lug nuts to full specification using the star pattern.

Note: If the wheel is not a 5 lug nut wheel, then use the proper tightening pattern listed in the image below.

Wheel lug tightening patterns

Image Source: PROwheels

Note: When working on alloy or aluminum wheels we strongly advise re-torquing the wheels after a short test drive.

Note: Never use lubricants or penetrating fluids on wheel studs, nuts or moving surfaces. Likewise, wheel nuts, studs and mounting surfaces should be clean and dry. If penetrating fluid is used to remove the wheel lugs, clean the studs and nuts before reinstalling. If desired, a thin layer of moly-lube may be used on the inner mating surface of the rotor where it meets the hub to slow down corrosion.

Calibrating Your Impact Wrench

WARNING: Wear safety goggles when using torque sockets

Torque socket are calibrated to an impact of 250 lb.ft. with 90-100 psi of air inlet pressure. Because most impact wrenches vary from 100 lb.ft. to 600 lb.ft. with various air inlet pressures, it is necessary to perform a simple calibration in order to ensure that torque accuracy will be uniform with each respective socket. The steps below will go over how to calibrate the impact wrench:

Various colors and sizes of torque sockets

1. First, tighten a wheel nut whith a torque socket. (For example, try 100 lbft. socket)

2. Second, test the torque setting of the wheel nut with a calibrated torque wrench (Preferably a dial indicator), by measuring the break away torque in the tightening direction.

3. If the torque of this wheel nut is more than 100 lb.ft., turn the impact wrench output down.

4. Repeat the above procedure until the wheel nut, torqued socket, and torque wrench are in sync. – Plus or minut 5 ft.lb of the 100 ft.lb. torque socket. As a result, the impact wrench is now calibrated for any of the torque sockets.

5. Each time the torque sockets are used, remember to set the impact wrench to the proper setting.

As long as the air inlet pressure is not changed, this setting will always be accurate for the torque sockets.

TIP: Failure to properly torque the wheels can take an otherwise perfect brake job and cause it to comeback with a reoccurring pulsation complaint.

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Hub Removal on Late Model Honda Trapped Rotors

Hub Removal on Late Model Honda Trapped Rotors

Working on hub removal for late model Honda’s can become slightly more difficult than other hub removals. This is because it is not uncommon for this particular hub to become stuck, or “trapped”. This article will go over what causes these hubs to stick, as well as how to remove them. The process for this particular hub removal is not very difficult and, by using a simple trick, becomes fairly straightforward and easy.

Cause and Solution

As can often happen, these hubs sometimes experience rust and corrosion between the hub assembly and the steering knuckle. As a result, and with time, this corrosion begins to bond the two parts together. Effectively, the parts become rusted together as well as more difficult to separate. To fix the problem, the knuckle and hub must be separated from one another. 

Hub Removal

1. Remove the knuckle assembly from the vehicle (Note that while this step can be skipped, we strongly advise removing the knuckle.)

2. Remove the four (4) OE hub retaining bolts. (Figure 32.1)

3. Install the four (4) 10×1.25mm x 3″ bolts, making sure to thread them in 1/2″ as shown in figure 32.2

4. Finally, using a hammer, drive the hub out of the knuckle using the heads of the longer bolts as drivers. Use an “X” pattern when doing this. As a result, this process will “walk” the hub out of the knuckle. (See figure 32.3)

Hub assembly with bolts in
New bolts installed in hub assembly
New bolts screwed through hub assembly

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Non-Directional Finish

Non-Directional Finish

Non-directional finish is a process to help mechanics ensure a quality rotor job is done. When a non-direction finish is not applied, it is not uncommon for a customer to experience poor stopping power or brake noise after leaving the shop. In fact, many times the rotors friction surface isn’t correct. As a result, poor contact is made with the brake pads. Likewise, the customer is likely to experience less stopping power and more brake noise.

Poor surface contact reduces the surface area available for creating friction. As a result, the brake pedal has to be pushed harder in order to stop the vehicle. Additionally, the poor surface contact can also cause the pads to vibrate while stopping, which causes the brake noise.

Non-Directional Finish: An Insurance Policy

Before beginning, it is important to note that performing a rotor service consists of more than a non-directional finish. In effect, non-directional finishes should be looked upon as an insurance policy. For example, it should enhance the rotor’s finish, NOT try and fix it. The following steps will go over the process of completing the rotors finish:

1. Resurface the Rotor

If you are resurfacing the rotor(s), use the proper machining techniques and make sure that the lathe is in good working condition. On hub-less rotors, make sure to clean the mating surfaces with the appropriate tool. Next, scratch cut the rotor(s) to ensure an accurate setup. Always use sharp bits and a vibration damper when machining.

2. Non-Directional Finish

After machining, apply a non-directional finish by using 120 grit drywall sandpaper on a rubber sanding block for 60 seconds per side. Apply the finish by applying moderate pressure. At the same time, use a slight rocking motion. (See Figure 31.1)

Hand holding sand paper on a rotor

3. Clean the Rotor

Finally, clean the rotor before installing it onto the vehicle. This is done in order to prevent machining dust from contaminating the brake pads. To begin, using a mild soap and water solution, wash both friction surfaces and wipe everything dry with a clean, lint free rag. Likewise, if using brake cleaner, us more than usual and wipe the surface down with a clean lint free rag or paper towels while still wet. In contrast, never use petroleum based cleaners as they will leave a residue.

More Information

There are many theories and opinions about non-directional finish. Typically, they center around the reasons and methods of completing the process. In this case, if we start by defining what is meant, we can clarify the two areas. For example, most lathes produce a directional finish. In this case, directional means that the finish has a pattern to it. Usually, the pattern produced is a spiral similar to an old vinyl record. If too pronounced this spiral could cause brake noise or even a loss of stopping power.

On the other hand, a finish that is non-directional will not have a pattern or “direction” to it. One common myth is that the finish must be a swirl finish. This myth is born from some new rotors coming out of the box with a pronounced swirl finish. In reality, you don’t have to see the finish for it to be effective.

Non-directional finishing should be viewed as an "insurance policy". It represents a simple step to help ensure the best possible surface to finish.

Non-Directional Finish Improves Results

With this understanding we can now discuss why and how to perform a non-directional finish. First, it is important to know that by correctly applying a finish with no direction the surface finish can be improved by up to 20%! As a result, the improved surface will provide a better mating surface for the friction material resulting in less chances for brake noise and reduced stopping power. And the best part? It only takes 2 minutes! That being said, it should be mentioned that most quality brake lathes produce a surface finish that falls well within acceptable limits. So, why bother applying a non-directional one? As stated above, performing this process may not always be necessary, but it is an insurance policy that only takes a few minutes to perform.

Figure 31.2 - Rotor

To Help, Not To Fix

At this point, it is important to emphasize that this process will not correct a poor surface finish. For example, if the base finish is substandard, you will gain little by applying a bit of sandpaper. In fact, proper surface finish is accomplished by a combination of a well maintained lathe, sharp cutting tips, and having the correct setup. Only after a quality base finish is obtained can the benefits of a non-directional finish be realized.

Don't Use an Angle Grinder

Contrary to popular belief, the angle grinder is not the best tool for the job. In fact, it is not even an acceptable method! Not one friction or rotor manufacturer, or any of the OEM’s endorse the use of an angle grinder as a method of applying non-directional finishes. This is because there are too many variables involved with angle grinders to perform the process correctly. Because the speed, type of disc, disc condition, time spent, and angle of the tool can be changed, results will always be inconsistent when using an angle grinder.

In figure 31.2 a rotor is shown that had an angle grinder used on it. The surface finish was measured before and after the application of the finish. Believe it or not, the surface finish was actually rougher after the finish was applied! For example, the smoothness of a rotor is measured in what is referred to as its RA factor. The lower the number, the better. The typical specification range is 15 to 80. On the rotor depicted above the RA started at 42, and ended at 45!

Sanding Block

The image below shows a rotor having a finished applied via a sanding block with 120 grit. Similar to the above rotor, this one was also measured. In fact, before the finish was applied it had an RA factor of 42. After sanding the rotor, the measurement dropped down to 33. As a result, the RA changed by 9, or roughly 21%. The non-directional finish is applied by using a full contact rocking motion while applying moderate pressure to the sanding block.

Non-directional finish using a 120 grit sanding block

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Measuring Hub Runout

Measuring Hub Runout

Excessive installed runout on hub-less rotors can be a problem. Because of this, we’ve prepared this article in order to help you diagnose and fix the issue. By following this guide, you can rest easy knowing that the job was completed efficiently and accurately. 

Solving Hub Runout

To determine if the hub is the cause of excessive runout, measure the hub runout. To do this, perform runout measurement and an indexing procedure as described here. If indexing determines that the hub is the cause of runout, hub runout should then be measured. The hub’s design will determine how the measurement should be performed. Figures 30.1 and 30.2 show two different hub flanges. First, figure 30.1 has a flat surface area outside the wheel studs while the hub in figure 30.2 has little to no flat surface outside the wheel studs. For your example, use the procedures below to measure hub runout.

Rotor illustration
Rotor illustration 2

Shouldered Hub

1. Setup the dial indicator as shown in the image below.

2. Position indicator plunger at a slight angle near the outside edge of the hub flange. Additionally, make sure that the dial indicator will not contact the wheel studs.

3. Next, using the appropriate size socket, rotate the hub in the direction that the dial indicator plunger is pointing. (in figure 30.3 the correct direction would be clockwise)

4. Note the difference between the lowest number and highest number obtained. This is the amount of hub runout. Most manufacturers do not provide a specification for hub runout. Generally speaking hub runout should be .001″ or less. Remember that the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.

Dial indicator illustration

Non Shouldered Hub

1. Begin by setting up the dial indicator as shown in the image below.

2. Position the indicator plunger so that it is perpendicular to the hub’s mounting surface, evenly spaced between 2 wheel studs so that it contacts within a 1/4″ of the outside diameter of the hub flange as shown in figure 30.4

 

Dial indicator 2 illustration

3. Next, position the dial indicator scale so that the needle is aligned with the “0”. Gently pull the indicator plunger 1/4″ away from the flange surface, then bring it back to rest on the flange surface. The needle should return to “0”. If the needle is at “0” proceed to step 4. On the other hand, if the needle is not on “0” then repeat steps 1-2 making sure the vise grips are tight, the flexible mount is rigid when the lever is turned, and the dial indicator clamp is snug.]

4. Pull the plunger out and rotate the hub so that the indicator plunger is located midway between the next 2 wheel studs. Now, gently bring the plunger back to the hub flange. Continue by noting the indicator reading.

Repeat

5. Repeat step 4 for the remaining wheel studs making sure to note the indicator reading until the hub has been rotated a full 360 degrees. Recheck the indicator reading at the starting point to make sure that the needle is at “0”. If the needle is not on “0” then start the process over. This will be caused by the indicator mounting having shifted.

6. Note the difference between the lowest and highest number obtained. This is the amount of hub runout. Most manufacturers don’t provide a specification for this. Generally, the runout should be .001″ or less. Remember that the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.

tip

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Rotor Indexing

Rotor Indexing

When you run into runout problems, there can be a few different culprits. Because of this, it is important to determine the correct source in order to fix the issue. One of the best ways to do this, is by rotor indexing. By performing an index not only will you find the problem, but often times, you’ll fix it as well. Typically, installed runout can be caused by any combination of the following:

 

  • Rotor has runout
  • Hub has runout
  • Hub to motor mating surface is not clean
This article will go over a process known as “indexing” in order to help you identify and correct any installed runout you may come across.

Rotor to Hub Index

The following steps will go over the indexing process. Following these steps will help you find the issue and, in most cases, fix it as well. To get started, follow the steps below to index the rotor to the hub.

Tip: Using this procedure will either correct the runout problem or tell you whether the problem is related to the hub or rotor

1. Measure rotor runout

2. If runout is greater than the allowable specification (usually no more than .002″) then proceed to the next step.

3. Index the rotor to a wheel stud.

4. Rotate rotor until the dial indicator reading is at its highest value. Use a magic marker to mark this point on the rotor and hub flange as shown in the image below:

Rust buildup

5. Next, remove the rotor. Check the hub and rotor mating surface for dislodged rust or anything else that could cause the runout. If the mating surface is good install the rotor by rotating it 2 lug positions from its original position.

6. Finally, Measure the runout. If it is now within the specifications, proceed to the next wheel. If not, rotate the rotor until the dial indicator reading is at its highest value. Continue by checking the position of the marks on the rotor and hub in relation to the high spot. If the high spot aligns with the rotor, the rotor is the source of the runout. If the high spot aligns with the mark on the hub, then the hub has runout.

Indicator Dial

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Rust and Runout

Rust and Runout

One possible cause for high speed pulsation is happens when rust builds up. This article will go over how rust causes this problem and the necessary steps to resolving the problem.

Cause

The problem occurs when one or more of the rotors installed have excessive runout. Generic specification being used by domestic OEMs is .002″. Excessive runout causes disc thickness variation (DTV) over time. The average for most vehicles is 3,000 to 6,000 miles. This number can vary up or down based on the variables involved.

Rust buildup in jacking

Rust on hub’s mating surface is a leading cause of runout. The rust can from to a point where it actually pushes the rotor away from the hub even with the wheel bolted on (See image above). This process has been termed “jacking”. It works much the same way as a tree root under a side walk. There are tremendous forces involved as the rust “grows” between the rotor and hub.

Solution

Cleaning of the rotor and hub’s mating surfaces is a critical part of the brake job. The hub to rotor mating surface must be free of rust or runout induced DTV can occur shortly after the brake job. As little as .001″ of rust at the outside edge of the hub will result in .002″ to .004″ of runout.

The method used to clean the hub depends on the severity of the rust buildup. The hub’s mating surface can be a difficult surface to clean due to the wheel studs. The area between the wheel stud and hub centering flange is the most difficult area to gain access to. Here are the best methods to clean the hub’s mating surface.

Method 1 - Mild Rust Build Up

1. Use an angle grinder equipped with a Scotch Brite disc to clean the majority of the surface area. Get as close to the studs as possible and change the disc when needed.

2. Finish the process by using the tool shown in the first image below to clean the area around the studs. This tool fits over the wheel stud to allow easy cleaning of the hard to reach area of the hub. The second image shown the finished result.

OTC Tool

Method 2 - Severe Rust Buildup

The hub shown in the first image below will not be able to be cleaned effectively using the steps outlined above. The end result would look something like the second image below. The OTC tool does NOT work on mild to heavy rust. It has a tendency to polish the rust instead of removing it. The most effective method is to use the following steps.

Rust Hub
Polished Rust

1. Abrasive blasting is the most effective method for rust removal. There is a specialized blast cabinet available that allows cleaning of the hub while it is still on the vehicle. The tool uses a drawstring boot to allow the unit to be used on the vehicle as shown in the image below.

Rust Buster

2. The following image show what the final product should look like. This is the same hub as shown above. This hub will not be the source of rust induced runout. While there are other methods that can be used to clean rusty hubs the method described above the most effective. Other methods can be time consuming, yield a lower quality job and may not result in all of the rust being removed.

Finished Product

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How to Verify Accuracy of Setup on Bench Lathe

How to Verify Accuracy of Setup on Bench Lathe

Bench lathe induced runout is one of the leading cause of runout induced DTV pulsation comebacks. Typically, there are three main reasons for bench lathe induced runout:

1. Arbor runout

2. Adapter condition

3. Not verifying accuracy of setup

This article will cover a process called “Scratch Cut” which is used to verify accuracy of setup.

Solution

All rotors and drums machined on a bench lathe should be scratch cut before machining. This is necessary to verify the accuracy of the lathe setup. Skipping this step can lead to machining runout into the rotor. The process of verifying the setup is commonly referred to as “scratch cut”. The list below shows each step of the process:

1. Position the bits away from the outside edge of the rotor.

2. Bring the outside bit in until it barely touches the rotor. While holding the outer knob, place the inner dial on zero. On lathes without this feature, take note of the dial reading.

3. Back the cutting tip away from the rotor a small distance and turn the lathe off.

4. Observe the scratch cut. If the scratch cut is at least 50% around the rotor proceed with the machining process. (first image) If the scratch cut is less than 50% then the setup needs to be verified. (second image)

Scratch on rotor more than 50 percent around
Rotor with a scratch less than 50 percent

Steps 5-10

5. Two things will cause a scratch cut less than 50%. The first is that the rotor has runout and needs to be machined.

6. The second is a problem in the setup. Adapter cleanliness, arbor runout and tightening of the arbor nut are the main causes of setup problems.

7. To verify the setup, loosen the arbor nut. While holding the inner and outer adapter rotate the rotor 180 degrees. Re-tighten the arbor nut. This process changes the relationship of the rotor and adapters.

8. Turn the lathe on and move the twin cutter in or out a small distance.

9. Make a second scratch cut by turning the dial to zero. On lathes without this feature, turn the dial into the same number as the first scratch cut. This process makes each scratch cut the same depth which makes comparing the cuts easier.

10. Back the cutting tip off a small distance and turn the lathe off. Compare the next two scratch cuts. If the problem is in the rotor, the cuts should be on top of one another. (See below)

11. A setup problem will cause the second cut to be in a different position from the first. (See first image below). If this is the case, disassemble everything and check for cleanliness, correct adapters and for nicks on the mating surface. (See second image below) Do not proceed with the machining process until the scratch cuts are in the same position. Doing so will include runout into the rotor.

Scratch Cut Not Matching
Clean Surfaces

Bonus Tip: EVERYTHING machined on a bench lathe should be scratch cut to verify accuracy. For additional info, see our article on bench lathe adapter service.

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Bench Lathe Adapter Service

Bench Lathe Adapter Service

When high speed pulsation occurs after 3,000-6,000 miles bench lathe induced runout is a likely culprit. This article will go over everything you need to do to fix this issue. Likewise, images are provided in order to help you visualize the steps necessary.

Bench Lathe Adapter Solution

Preventing the majority of bench lathe setup problems is a relatively easy process. For example, follow the following steps.

1. Arbor Shaft Runout

First, Measure the arbor runout and correct it if necessary. Typically, the specification for arbor runout near the end of the arbor is .002″. However, if the runout is outside of the specification, remove and clean the mating surfaces. If the problem persists, consult your bench lathe manual.

Arbor Shaft Runout

2. Arbor Face Runout

Second, measure the arbor face runout. Usually, the specification for this measurement is .0005″. If the measurement is off, a correction will have to be performed using the bench lathe manufacturer’s procedures.

Arbor Face Runout

3. Hubless Adapter Arbor Mating Surface

In some cases, you’ll come across adapters like the one pictured below. This adapter is typical in many shops. These kinds of adapters rly on the mating surface as well as the arbor face to be accurate and true. Because of the state of the one pictured, it would be impossible for an accurate setup with this adapter.

Dirty adapter face

4. Correcting Arbor Mating Surface

In order to fix a mating surface, it will have to be cleaned. To do so, place a piece of sandpaper on a flat surface and run the adapter’s small face up and down a few timers while applying even pressure. As a result, you’ll end up with something resembling the image below. Likewise, it is important not to worry about pits or indentations as these won’t effect the mating.

Clean Adapter Face

5. Indexing Adapter to Lathe:

(This step is optional if the arbor face runout was .0000″.) Next, if the arbor face runout was greater than zero, then the hubless adapters will have to be indexed to the lathe before continuing. This is important because some adapters have index marks cast into them while others don’t. As a result, if there is no index mark use a file to make an index mark on the edge of the small mating surface as shown in the image below.

Adapter Index Mark

6. Preparing Adapter for Machining

Next, install the adapter on the lathe and position the twin cutter to enable machining of the large mating surface as shown below. At times, it will be necessary to remove the opposite tool holder to achieve the proper clearance.

Twin cutter setup

7. Machining Large Mating Surface

Next, remove only as much material as is necessary to achieve a 360 degree cut. Typically, this only requires .002″ to .005″. Make a slow cut to machine the large mating surface. As a result, the mating surfaces becomes true to the lathe as shown below.

Finished product

8. Optional Adapters

Similarly, the same procedure can be used on the optional adapters available for most bench lathes such as the composite rotor adapter shown in the picture below.

Other adapters

Conclusion

The average bench lathe setup will take between 1 and 2 hours to preform. Once this procedure is performed it will become a simple matter of keeping the mating surfaces clean and free of nicks and burns. If the arbor face had runout and index marks were used then the adapter and arbor index marks should be aligned each time the adapters are used.

Even after this procedure has been completed, it is still necessary to check the setup. To do so, you’ll need to perform a scratch cut.

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Brake Job Done Well

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