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

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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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