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Effective Slider Service – Fighting the Elements

Effective Slider Service – Fighting the Elements

Problem:

Corrosion causing premature pad wear

Cause:

Moisture intrusion causing caliper housing to corrode

Solution:

It is a common belief that if the caliper hardware looks like the caliper pictured in Figure 35.1 that no service is necessary. In other words, if the dust boot is in one piece and the slider spin moves everything is okay. This is a myth. The caliper pictured in Figure 35.1 could have a number of conditions that would require service and still move. One of the issues that must be considered when performing service are there any existing conditions that could bring this vehicle back before its time? A closer look at the caliper pictured in Figure 35.1 resulted in the following findings:

35.1

  • Figure 34.2 – One of the slider pins has a portion of the anodized coating worn off. The anodized coating prevents corrosion. The worn portion is now susceptible to corroding. Industry accepted guidelines say pin replacement is required when this condition is present.

    35.2

  • Figure 34.3 – This pin represents the next step in the process. The pin has corroded in the area where the coating is missing. Even with this “growth” the pin still moved.

    35.3

  • Figure 34.4 & 34.5 – Floating caliper housings utilize casting holes to house the rubber bushings, o-rings or boots. Moisture intrusion into the caliper housing casting holes results in corrosion in many types of floating calipers. 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.

    35.4 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. 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:

  1. Remove all caliper hardware from housing.
  2. Clean 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.

    35.6

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

    35.7

  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.

    35.8 35.9

  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.

    35.10

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

    35.11

  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).

    35.12

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.

Caliper Replacement Guidelines

Caliper Replacement Guidelines

Problem: 

Determining when to replace calipers

Cause:

There are many variables that effect the operation of a caliper making it impossible to set a generic life span based on mileage or length of service.

Solution:

Replacing calipers with every brake job would be considered overselling by most customers and regulators while never replacing calipers unless there is gross failure would be considered underselling by most shops. I feel there are two groups of customers who should be offered the option of replacing the calipers. Notice I used the word option which means 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:

• High mileage
• Original equipment calipers
• Each set of pads lasts less than the previous set
• Customer is keeping the vehicle

Presenting option to customer:

When presenting the option of replacing the calipers based on the circumstances above you should make the following points:

• Explain to the customer that based on the vehicle’s history and current condition the only way to restore maximum pad life would be to service the inside of the caliper. (This usually means replacement) By replacing the calipers the function of the square cut seal would be restored which means the caliper would apply AND release properly. (See more info for a better explanation of the square cut seal).

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

• Parts or labor are required to restore the caliper’s ability to float or slide. If the caliper is not floating properly and requires the replacement of pin(s), rubber boots or bushings and/or anti-rattle hardware the customer should also be given the option of replacing the caliper (See Figures 34.1). In some cases it can be more expensive to fix the existing caliper than to replace it.

34.1

Presenting option to customer:

When presenting the option of replacing the calipers based on the circumstances above you should make the following points:

• In this case the customer should be presented with the price to service their existing calipers and then the cost to replace the calipers. You should explain that for the additional $ the inside of the caliper is being serviced not just the outside. Also include an explanation in the differences in warranty, longevity and risk for problems.

There are of course reasons to require replacement of the caliper and not just suggest it.

Here is a list of reasons why the caliper should be replaced:

• Piston dust boot is ripped or damaged
• Piston sealing surface is corroded
• Piston is sticking or seized
• Housing is damaged or corroded to a point where slider service is not practical
• Internal self adjustment mechanism is nonfunctional (rear disc with integral parking brake)

34.2

It should be noted that without a proper inspection most of the conditions listed above would NOT be found.

More Info: Floating Caliper Operation

Apply cycle: Calipers are not instant on, instant off parts. They go through a cycle or process during both brake apply and release (See Figure 34.3).

34.3

Understanding these 2 processes is key to being able to identify many of the causes of premature pad wear. The apply-cycle beings with the application of the brake pedal, which results in pressure being generated in the hydraulic system. The hydraulic pressure created in the caliper housing pushes in all directions. 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. The 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).

34.4

Once the inboard pad is against the rotor the caliper piston is no longer the easiest thing to move and system pressure increases. The next easiest thing to move is the caliper housing. The 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. The 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.

34.5

Release cycle: When the brake pedal is released a different process takes place to allow the brake pads to release. 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. The groove in the caliper housing is beveled towards the open end of the bore. The square cut seal forms a seal between the caliper housing and the piston’s sealing surface (See Figure 34.6).

34.6

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

34.7

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.

Wheel Tightening Procedures

Wheel Tightening Procedures

Problem:

Reoccurring pulsation compliant due to runout induced DTV (disc thickness variation)

Cause:

Wheels installed using incorrect tightening procedure.

Solution:

The process of installing a wheel involves 2 key steps which when done properly will eliminate wheel induced runout. The steps are:

1. Tightening sequence
2. Step torquing

Wheel Tightening Procedures

Proper tightening of the wheel lugs is necessary to promote safety and proper brake operation. All wheels are to be tightened using either a hand torque wrench or torque limiting socket following the procedure below:

1. Hand tighten all 5 lug nuts using star pattern.
2. Tighten all 5 lug nuts to approximately ½ specification using the star pattern.
3. Tighten all 5 lug nuts to full specification using the star pattern.

Note: If the wheel is not a 5 lug wheel then use the proper tightening pattern listed in Figure 33.1.

Note: On alloy and aluminum wheels it is advisable to re-torque the wheels after a short test drive.

Note: Never use lubricants or penetrating fluids on wheel studs, nuts or mounting surfaces. Wheel nuts, studs and mounting surfaces must be clean and dry. If penetrating fluid is used to remove the wheel lugs clean the studs and nuts before reinstalling. 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.

33.1

CALIBRATING YOUR IMPACT WRENCH

WARNING: Wear safety goggles when using torque sockets

Torque Sockets (Figure 33.2) are calibrated to an impact of 250 lb.ft. with 90-100 psi of air inlet pressure. Since 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 so torque accuracy will be uniform with whichever torque socket is used.

33.2

Calibrate the impact wrench using the following instructions:

1. Tighten a wheel nut with a torque socket (for example try 100 lb.ft. socket).
2. Test the torque setting of the wheel nut with a calibrated torque wrench (preferably a dial indicator type), 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, torque socket and torque wrench are in synch – plus or minus 5 ft.lb. of the 100 ft.lb. torque socket. 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 in not changed, this setting will always be accurate for the torque sockets.

tip

Hub Removal on Late Model Honda Trapped Rotors

Hub Removal on Late Model Honda Trapped Rotors

Problem:

Removal of hub assembly on late model Honda vehicles.

Cause:

Rust and corrosion form between the hub assembly and the steering knuckle. This corrosion bonds the two parts together.

Solution:

NOTE: While it is possible to perform the following steps on the vehicle it is best to remove the knuckle from the vehicle.

To remove the hub/rotor from the knuckle use the following steps:

1. Remove knuckle assembly from vehicle (strongly advised)
2. Remove four (4) OE hub retaining bolts (Figure 32.1)
3. Install four (4) 10×1.25mm x 3” bolts, making sure to thread them in ½” as shown in Figure 32.2.
3. 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. This process will “walk” the hub out of the knuckle (See Figure 32.3).

32.1 32.2 32.3

Non-Directional Finish

Non-Directional Finish

Problem: 

Poor stopping power or brake noise after brake job

Cause: 

One of the common causes of both a lack of stopping power and brake noise shortly after a brake job is performed has to do with rotor service. If the rotor’s friction surface is not correct it can result in poor surface contact with the brake pads.

Poor surface contact reduces the surface area available for creating friction and can result in the brake pedal having to be pushed harder to stop the vehicle. The poor surface contact can also cause the pads to vibrate during stopping which can cause brake noise.

Solution:

Rotor service involves more than just the non-directional finish. Non directional finish should be looked upon as an “insurance policy”. It should be used to enhance the rotor’s finish NOT try and fix it. Here are the steps:

1. If resurfacing the rotor(s) use proper machining techniques and make sure the lathe is in good working condition. On hubless rotors make sure to clean the mating surfaces with an appropriate tool. Scratch cut
all rotors to ensure accurate setup. Always use sharp bits and a vibration damper when machining.

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

31.1

3. Clean the rotor before installing on vehicle to prevent machining dust from contaminating brake pads. The best method to accomplish this is to use a mild soap and water solution. Wash both friction surfaces and wipe dry with a clean lint free rag or paper towels. If using brake clean use a little more than usual and wipe the surface with a clean lint free rag or paper towels while it is still wet. Never use petroleum based cleaners because they leave a residue.

More Info:

There are many theories and opinions about non-directional finish. They usually center around why you should do it and more importantly how to do it. If we start by defining what is meant by non-directional finish it will go a long way in clarifying these two areas. Most lathes produce a directional finish. Directional means the finish has a pattern to it. The pattern produced by a typical bench and many on-the-car lathes is a spiral similar to an old vinyl record. If too pronounced this spiral could cause brake noise problems and in some cases a lack of stopping power.

For the sake of space I am going to refer to a non-directional finish from this point as “NDF”. NDF is defined as a finish that does not have a pattern or “direction” to it. One of the common myths about NDF is that it must be a swirl finish. This myth comes from some new rotors coming out of the box with a pronounced swirl finish. The truth is that you don’t have to see the finish for it to be effective.

tip

With this understanding we can now discuss why and how to perform a NDF. I call a NDF an “Insurance Policy”. Applying an effective NDF will improve the surface finish by up to 20%! Improved surface finish will provide a better mating surface for the friction material resulting in less chances for brake noise and stopping power problems. All this with only a 2 minute investment! With this 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 NDF you may ask? The NDF improves on this finish which will improve braking performance.

32.2

An important point to make at this time is that NDF cannot correct a poor surface finish. If the base finish is substandard you will gain little by applying a NDF. Proper surface finish is accomplished by a combination of a well maintained lathe, sharp cutting tips and correct setup. Once a good base finish is obtained you can realize the true benefits of a NDF. So how do you apply an effective NDF?

Contrary to popular belief the most common method used to apply a NDF, the angle grinder is not the best. 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 to apply a NDF. There are too many variables involved in the use of an angle grinder to perform the process correctly. They include the speed of the tool, the type of disc, the condition of the disc, the amount of time spent, and the angle of the tool. Figure 31.2 shows a rotor with a NDF applied with an angle grinder. The surface finish was measured before and after the application of the NDF. Believe it or not the surface finish was actually rougher after the NDF was applied! The smoothness of the rotor is measured in what is referred to as its RA factor. The lower number the better. The typical specification range is 15 to 80. The before number on the rotor in Figure 31.2 was 42. The after number was 45.

Figure 31.3 shows a rotor with a NDF applied using a hand sanding block with 120 grit sandpaper. This rotor was also measured before and after. The RA factor before was 42 and the after measurement was 33. This represents a gain of 9 points or roughly 21%. The NDF is applied by using a full contact rocking motion while applying moderate pressure to the sanding block.

31.3

Measuring Hub Runout

Measuring Hub Runout

Problem:

Excessive installed runout on hubless rotors

Case:

Excessive hub runout

Solution:

Measure hub runout to determine if hub is cause of excessive runout. Perform runout measurement and indexing procedure as described in our Dec. 1 2015 Post Rotor Indexing. If indexing determines the hub is cause of runout, hub runout should 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. 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. Use the procedures below to measure hub runout:

30.1                                                                                                                                             30.2

Shouldered hub:

  1. Setup dial indicator as shown in Figure 30.3.
  2. Position indicator plunger at slight angle at outside edge of hub flange making sure dial indicator will not contact wheel studs.
  3. Using the appropriate size socket, rotate the hub in the direction 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 the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.

30.3

Non-shouldered hub:

  1. Setup dial indicator as shown in Figure 30.4.
  2. Position indicator plunger so it is perpendicular to the hub’s mounting surface, evenly spaced between 2 wheel studs and so it contacts within a ¼” of the outside diameter of the hub flange as shown in Figure 30.4.
    30.4
  3. Position the dial indicator scale so the needle is aligned with the “0”. Gently pull the indicator plunger ¼” away from the flange surface and 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. 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 the indicator plunger is located midway between the next 2 wheel studs. Gently bring the plunger back to the hub flange. Note the indicator reading.
  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 making sure the needle is a “0”. If needle is not on “0” then start process over, the indicator mounting has shifted.
  6. 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 the rotor runout caused by hub runout will be multiplied by the rotor’s larger diameter.

tip

 

Rotor Indexing

Rotor Indexing

Problem:

Determining and correcting the source of installed runout.

Cause:

Excessive installed runout can be caused by any combination of the following:

  • Rotor has runout
  • Hub has runout
  • Hub to rotor mating surface is not clean

Solution:

Performing a process known as “Indexing” can identify and in most cases correct the installed runout. Follow the steps below to index the rotor to the hub:

  1. Measure rotor runout Tip 1
  2. If runout is greater than allowable specification (generic specification is no more than .002”) then proceed to next step.
  3. Index the rotor to a wheel stud.
  4. Rotate rotor until 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 Figure 28.1.
    28.1
  5. Remove the rotor. Check hub and rotor mating surface for dislodged rust or anything else that could cause the runout. If mating surface is good install the rotor by rotating it 2 lug positions from its original position.
  6. Measure runout. If within specifications proceed to next wheel. If not rotate rotor until dial indicator reading is at its highest value. Check the position of the marks on the rotor and hub in relationship to the high spot. If the high spot aligns with the rotor, the rotor is the source for the runout. If the high spot aligns with the mark on the hub the hub has runout

29.1

Another Recall Due to Corrosion Is it Time to Test Your Brake Fluid?

Mitsubishi_logo_Mitsubishi_large
Consumer Affairs recently shared news of Mitsubishi Motors North America (MMNA) recalling 74,836 vehicles due to corrosion inside the anti-lock brake system.

To determine whether your brake fluid is potentially corrosive simply ask your shop to use a copper corrosion test strip from Phoenix Systems. In 60 seconds or less the test strip will provide an extremely accurate measurement of the corrosivity of your brake fluid.

To learn more about the Mitsubishi recall visit: http://www.consumeraffairs.com/recalls/mitsubishi-recalls-eclipse-and-eclipse-spyder-vehicles-062615.html

To learn more about testing corrosion levels in your brake fluid visit: http://www.brakebleeder.com/products/brake-fluid-testing/brakestrip-2-strips-per-card-retail-packaging/

Hyundai Fined $17.35 Million by Feds Over Brake-Fluid Recall

Hyundai Fined $17.35 Million by Feds Over Brake-Fluid Recall

Hyundai has agreed to pay a $17.35 million fine for delayed reporting of a brake defect affecting Genesis luxury cars, the National Highway Traffic Safety Administration said Thursday.

The defect involves corrosion in critical brake system components that can reduce braking effectiveness and increase the risk of a crash, NHTSA said. Hyundai was aware in 2012 that brake fluids used in the model year 2009-2012 Genesis cars did not sufficiently inhibit corrosion in key components of the vehicle’s brake system, the agency said.

Read more about the Hyundai fine and recall here:  http://blog.caranddriver.com/hyundai-fined-17-35-million-by-feds-over-brake-fluid-recall/.

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