Disc Brake Warranty Service and Procedures - LRO, Lateral Runout, Rotor, Corrosion, Pulsation, Pads, Wear, Noise, Refinish, Clean-up, Squeak, Grind, Groan

This bulletin is being revised to include the 2009 model year. Please discard Corporate Bulletin Number 05-05-22-002C (Section 05 -- Brakes).

Important: 

For your convenience, this bulletin updates and centralizes all GM's Standard Brake Service Procedures and Policy Guidelines for brake rotor and brake pad service and wear. For additional information, the Service Technical College lists a complete index of available Brake courses. This information can be accessed at www.gmtraining.com > resources > training materials > brakes courseware index.

Important: PLEASE FAMILIARIZE YOURSELF WITH THESE UPDATES BEFORE PERFORMING YOUR NEXT GM BRAKE SERVICE.

The following five (5) key steps are a summary of this bulletin and are REQUIRED in completing a successful brake service.

1. Measure and Document Pre-Service Rotor Thickness* (REQUIRED on Repair Order) - determine rotor clean-up/refinish/replace
2. Properly clean ALL brake corner mating surfaces - hub, rotor and wheel
3. Properly clean-up/refinish rotor, measure and document post-service rotor thickness (REQUIRED on Repair Order)

Important: If you are consistently measuring high LRO after rotor refinishing, verify lathe equipment is properly calibrated.

4. After brake pad replacement and/or rotor clean-up/refinish/replace, measure and document Lateral Run Out [LRO]-- (REQUIRED on the Repair Order. If post-service Lateral Run Out (LRO) measures above specification, maximum 0.050 mm (0.002 in) **, Correct for LRO using Brake Align® Plate (part number REQUIRED on Repair Order). For more information and the Brake Align® application chart, refer to TSB 01-05-23-001*.
5. Properly reassemble the brake corner using proper torque tools, torque specification and torque sequence -- wheel lug nuts.

* The bulletin refers to Minimum Thickness specification as the minimum allowable thickness after refinish. Always refer to SI to verify the spec stamped on the rotor is the minimum thickness spec after refinish and not the discard spec.

**The bulletin will refer to LRO maximum specification as 0.050 mm (0.002 in). However, some trucks may slightly differ. Refer to SI to verify specifications.

Bulletin Format/Key Page Number

Reference:

Important: When using any one of the brake labor operations listed in this bulletin (except for H9709 -- Brake Burnish), the following three rotor measurements (1. Original Rotor Thickness, 2. Refinished Rotor Thickness and 3. Lateral Run Out) are required and MUST be written/documented on the customer service order, or for your convenience, complete the form (GM Brake Service customer service order Documentation for Required Measurements) found on the last page of this bulletin and attach it to the customer service order. If the Warranty Parts Center generates a request, this Documentation/Form must be attached to the customer service order that is sent back.

Important: Documentation of brake lathe maintenance and calibration as recommended by the lathe manufacturer must be available for review upon request.

Customer Service Order Documentation -- Rotor Original And Refinished Thickness -- REQUIRED

When resurfacing a brake rotor or drum, the ORIGINAL thickness (measured thickness before refinish) and REFINISHED thickness (measured thickness after refinish) MUST be written/documented on the customer service order hard copy for each rotor serviced. If a rotor replacement is necessary, only the Original thickness measurement needs to be recorded.

Customer Service Order Documentation -- Lateral Run Out (LRO) and Correctional Plate Part Number -- REQUIRED

When using any one of the brake labor operations listed in this bulletin (except for H0192/H0202 - Brake Drum Refinishing and H9709 -- Brake Burnish), the rotor assembly MUST be measured for Lateral Run Out (LRO) (follow brake procedure steps 9-11). If the LRO measurement is greater than 0.050 mm (0.002 in), correct it by using the proper Brake Align® Correctional Plate (DO NOT refinish new rotors or newly refinished rotors to correct LRO). This LRO measurement, and the Correctional Plate part number used to correct the LRO, MUST be written/documented on the customer service order hard copy. If no correction is necessary, only the LRO measurement for each rotor serviced needs to be recorded.

Important: Correction plates can only be used on Hubless rotor design. A correction plate part number can not be used with Hubbed, Trapped or Captured type designed rotors.

Warranty System Documentation -- Lateral Run Out (LRO) -- REQUIRED

When using any one of the brake labor operations listed in this bulletin (except for H0192/H0202 - Brake Drum Refinishing and H9709 -- Brake Burnish), the Lateral Run Out (LRO) measurement (as measured in the "customer service order Documentation -- Lateral Run Out" section above) MUST be documented in the technician comments section of the warranty claim.

Customer Service Order Documentation -- Explanation of Part Replacement -- REQUIRED

If replacement of a brake component is necessary, proper documentation on the customer service order is required. See the following examples:

Brake Service Procedure

1. Remove the wheel and caliper.
2. Measure rotor thickness. In order to determine if the rotor can be refinished, follow these steps:

Important: If performing routine Brake Service for worn pads only, and the rotors are not damaged and measure within specification - DO NOT REFINISH ROTORS.

2.1.	Remove the rotor(s).

2.2.	Measure the rotor for original thickness using a brake micrometer.

2.3.

Reference the Minimum Thickness specification stamped on the backside of the rotor or SI for Minimum Thickness specification/other. In most cases, the rotor should be refinished unless the measurement taken makes it obvious that refinishing the rotor would take the measurement under the Minimum Thickness specification (then replacement is necessary). DO NOT use any other manufacturers' rotor specifications.

3. ***Record the ORIGINAL rotor thickness measurement on the customer service order hard copy as noted in the "customer service order Documentation -- Rotor Refinish" section of this bulletin.
4. Clean all of the mating surfaces between the hub, the rotor and the wheel using the J 42450A -- Wheel Hub Cleaning Kit and J 41013 -- Whiz Wheel®.

If rotors are not to be refinished, go to Step 8.

Important: Cleaning all mating surfaces and making them free of corrosion, burrs and other debris (which includes removal of Hubless rotors) is critical and MUST be performed whether using an On-Car or Bench Lathe Refinish Procedure.

5. Be sure to follow the appropriate refinishing procedure listed below for the type of lathe you are using.

Important: Only replace the rotors if they do not meet the Minimum Thickness specification.

Important: DO NOT REFINISH NEW ROTORS.

Important:  Only remove the necessary amount of material from each side of the rotor and note that equal amounts of material do not have to be removed from both sides on any brake system using a floating caliper.

Important: Prior to making the cut, install the recommended clip-on style disc silencer supplied with the lathe. Use of this silencer is critical to prevent chatter from occurring during the cut.

Bench Type Lathe

5.1.	Refinish the existing rotor on an approved, well-maintained lathe to guarantee smooth, flat and parallel surfaces.

5.2.	Check for clean and true lathe adapters and make sure the arbor shoulder is clean and free of debris or burrs. For more information, see the "Brake Lathe Calibration Procedure (Bench-Type)" section in this bulletin.

5.3.	On the outboard area of the rotor, position the cutting tools one-eighth of an inch into the brake pad area of the rotor. Feed the cutting tools into the rotor until they cut the rotor to new metal, a full 360 degrees. Zero each dial and back off a full turn.

5.4.	Move the cutting bits to the middle of the rotor and do the same procedure. If zero is passed during the process, reset zero. Back off a full turn.

5.5.	Position the cutting bits one-eighth of an inch inside the inboard (closest to the hub) edge of the brake pad contact area. Do the same procedure. If zero is passed during the process, reset zero.

5.6.	Back off a full turn and position the cutting bits all the way inboard in preparation to refinish the full rotor surface. Advance both tool cutters to the zero setting plus just enough to clean up the entire rotor surface.

5.7.	After completing the refinish, sand both sides of the rotor for approximately one minute per side using a sanding block and 130-150 grit sandpaper to obtain a non-directional finish.

On-Car Type Lathe

5.1.	Reinstall the rotor(s).

Important: When using the On-Car lathe on vehicles equipped with limited slip (or posi-trac) rear system, it is critical that the rear drive shaft is disconnected/disengaged prior to operation of the On-Car lathe. Remember to mark and re-index the drive shaft correctly on re-assembly to prevent creating driveline vibration. Whenever the lathe drive motor is being switched on, the operator MUST keep their body out of the wheel well area until the machine has reached its normal operating RPM.

5.2.	Refinish the existing rotor on an approved, well-maintained lathe to guarantee smooth, flat and parallel surfaces.

Important: When raising the vehicle on the lift, be sure to have it at a good working height (waist high is average) to accommodate mounting the On-Car lathe. Optimally, the center piston on the lathe trolley will be mid-travel. If the lathe trolley center piston is completely compressed (bottoming out) or inversely fully extended and hanging off the vehicle hub, this could affect the calibration time of the lathe.

5.3.	Select the correct adapter for the vehicle you're working on and mount it to the hub with the vehicle lug nuts. Hand tighten 34-41 N·m (25-30 lb ft) the nuts using equal torque. DO NOT use impact wrenches as excessive torque will damage the adapter.

Important: Ensure the adapter sits flush on the rotor hat surface. Be sure to remove any rust, rotor retaining clips, etc. that may preclude the adapter from sitting flat on the mounting surface.

5.4.	Connect the lathe to the adapter. Turn on the lathe and activate the computer to compensate for run-out in the hub.

5.5.

Once the computer indicates the compensation process was successful, on the outboard area of the rotor, position the cutting tools one-eighth of an inch into the brake pad area of the rotor. Feed the cutting tools into the rotor until they cut the rotor to new metal, a full 360 degrees. Zero each dial and back off a full turn.

5.6.	Move the cutting bits to the middle of the rotor and do the same procedure. If zero is passed during the process, reset zero. Back off a full turn.

5.7.	Position the cutting bits one eighth of an inch inside the inboard (closest to the hub) edge of the brake pad contact area. Do the same procedure. If zero is passed during the process, reset zero.

5.8.	Back off a full turn and position the cutting bits all the way inboard in preparation to refinish the full rotor surface. Advance both tool cutters to the zero setting plus just enough to clean up the entire rotor surface.

5.9.	After completing the refinish, sand both sides of the rotor for approximately one minute per side using a sanding block and 130-150 grit sandpaper to obtain a non-directional finish.

5.10.

Dismount the lathe but leave the lathe adapter attached to the vehicle.

6. Once the rotor has been properly machined, wash the rotor with soap and water (use a mild dish washing soap) or wipe it clean with GM-approved brake cleaner, P/N 12378392.

Important: Thoroughly cleaning the rotor will prevent the possible transfer of finite metal dust left as a by-product of machining to the pad material during the seating process, thus reducing the opportunity for squeaks or other noises to occur.

7. ***Record the REFINISHED rotor thickness measurement on the customer service order hard copy. Refer to the "customer service order Documentation -- Rotor Refinish" section of this bulletin.
8. Setting up to measure for Lateral Run Out (LRO):

Bench-Type Lathe

8.1.	Ensure that the mating surfaces of the rotor hat section and the hub mating surface are clean and free of debris.

8.2.	Mount the new, original or refinished rotor onto the vehicle hub.

Important: Always hold the rotor on the bottom half so any debris that may be dislodged from the vents will fall out instead of falling into the mounting area. Any movement or jarring from the rotor falling over on the studs can release rust from the vents on the rotor.

8.3.	Tilt the top of the rotor in towards the vehicle so you can see the studs and ease the rotor onto the studs.

8.4.	Slide the rotor all the way to the hub and hold it in place until you have placed one of the conical washers (with the tapered hole side facing out) and run the first lug nut up tight by hand so the rotor doesn't move when you release it.

8.5.	Place the conical washers on the rest of the studs (with the tapered hole side facing out), start and snug the lug nuts by hand.

8.6.

Using the one-half inch drive impact wrench and a torque stick (J 39544) or equivalent, start with the lug nut opposite of the one you first tightened by hand and tighten the lug nuts using a star pattern until they touch the hub but do not completely torque. Then again, starting with the first lug nut you tightened by hand, tighten all the lug nuts in a star pattern to the specific vehicle torque specification.

8.7.	DO NOT reinstall the caliper or the wheel at this time.

On-Car Type Lathe

8.1.	Leave the On-Car adapter on the wheel.

8.2.	Proceed to Step 9.

9. Fasten the dial indicator to the steering knuckle so that the indicator needle contacts the rotor outboard friction surface approximately 6.35 mm (0.25 in) from the rotor's outer edge. The stylus should be perpendicular to the friction surface of the rotor.

Important: Make sure the dial indicator needle tip is screwed tight, a loose tip could cause false readings.

10. Measure for LRO. Follow the procedure below to determine if the LRO is within specification (0.050 mm (0.002 in) or LESS).

10.1.

Rotate the rotor and locate the point on the rotor where the lowest dial indicator reading is indicated and set the dial indicator to zero.

10.2.

Rotate the rotor from the low point and locate the point with the highest dial indicator reading (rotor "high spot"). Note the amount and mark the location of the "high spot" on the rotor and mark the closest wheel stud relative to this location. If the high point falls between two studs, mark both studs. In instances where the vehicle has "capped lug nuts" you should mark the hub.

11. ***Record the rotor Lateral Run Out measurement on the customer service order hard copy. Refer to the "customer service order Documentation -- Lateral Run Out" section of this bulletin. Measuring for LRO is critical and MUST be performed whether using an On-Car or Bench Lathe Refinish Procedure.

Important:  ***This measurement must also be documented in technician comments section of the warranty claim. refer to the "Warranty System Documentation - Lateral Run Out" section of this bulletin.

12. If the Lateral Run Out (LRO) measurement is 0.050 mm (0.002 in) or LESS, no correction is necessary. Go to Step 16 if this is the first rotor completed. Go to Step 17 if this is the second rotor completed. If the LRO is GREATER than 0.050 mm (0.002 in), go to Step 13.
13. If the LRO measurement is greater than 0.050 mm (0.002 in), use the following procedure to correct for LRO:

Important: If the LRO measurement is over 0.279 mm (0.011 in), determine the source or cause of the LRO and correct it (i.e. verify drive axle nut is torqued to spec; if refinished rotor is source of LRO due to a lathe qualification issue - see "Brake Lathe Calibration Procedure").

Hubless Rotor

13.1.

Remove the rotor and using the Brake Align® application chart (refer to Corporate Bulletin Number 01-05-23-001A*), choose the correct plate to bring the rotor LRO to 0.050 mm (0.002 in) or less. The plates come in 0.0762 mm (0.003 in), 0.1524 mm (0.006 in) and 0.2286 (0.009 in) compensation. For more information on proper plate selection, see the instruction video/DVD included in the "Brake Align®" kit.

13.2.

Align the V-notch of the selected Brake Align® correction plate to the marked wheel stud ("high spot") or between the two points marked (if the "high spot" is between two wheel studs).

Important: IF Brake Align® Correction Plates are not available for the vehicle being serviced, refer to Brake Rotor Assembled Lateral Runout Correction in SI for correcting LRO.

Important: Per Brake Align® manufacturer, NEVER attempt to stack two or more Correction Plates together on one hub. NEVER attempt to reuse a previously installed Correction Plate.

13.3.

Reinstall the rotor using the same method and precautions as the first time - found in Step 8. Make sure to index the rotor correctly to the marks made in step 10, otherwise LRO will be comprised.

Hubbed/Captured/Trapped Rotor

13.1.

Measure the rotor thickness.

13.2.

Refinish or replace the rotor (see Service Information for further details).

14. Use a Dial Indicator to measure the rotor to verify the LRO is within specification.
15. If using,

BENCH LATHE -- DO NOT remove conical washers and lug nuts at this time.

ON-CAR LATHE -- You must remove the adapter and install conical washers and lug nuts to retain rotor position.

Important: For Hubless rotor design, while removing the adapter, you must hold the rotor tight to the hub and install the top conical washer and lug nut first to ensure no debris falls between the surface while removing the adapter. Then, install the remaining conical washers and lug nuts. Otherwise, LRO will be comprised.

16. Perform Steps 1-12 on the opposite side of the vehicle.
17. After both sides of the vehicle have LRO measurements within specification, perform the following steps:

17.1.

Reinstall the calipers and pads.

17.2.

Pump the brakes to pressurize the calipers.

17.3.

Remove the lug nuts/conical washers.

17.4.

Install and properly torque the wheels.

Important: It is critical to follow the star pattern wheel torque procedure and use the proper tools (torque stick or torque wrench) as referenced in SI.

18. Road test the vehicle to verify the repairs.

***Indicates measurements must be written/documented on the customer service order and in the technician comments section of the warranty claim.

BENCH-TYPE LATHE

Use the following procedure to calibrate a Bench-type brake lathe:

1. After refinishing a rotor, loosen the arbor nut and while holding the inside bell clamp to keep it from rotating, rotate the rotor 180 degrees.
2. Retighten the arbor nut and set the dial indicator on the rotor using the same instructions as checking the run out on the vehicle.
3. Rotate the arbor and read the runout.
4. Divide the reading by two and this will give you the amount of runout the lathe is cutting into the rotor.

Important: If there is any runout, you will need to machine the inside bell clamp in place on the lathe (this procedure is for a Bench-type lathe ONLY. DO NOT machine inside the bell clamp on an On-Car type lathe).

Machining the Inside Bell Clamp (Bench-Type Lathe Only)

Any nicks or burrs on the shoulder of the arbor must be removed. An 80-grit stone can be used to accomplish this. Spray WD-40® on the shoulder and with the lathe running, hold the stone flat against the shoulder surface using slight pressure. When the burrs are gone, clean the surface. Burrs must also be removed from the hub of the inside bell clamp. This can be accomplished with the stone and WD-40®. Keep the stone flat on the hub while removing the burrs. After removing the burrs, clean the hub.

Place the bell clamp on the arbor of the lathe and use the small radius adapters first and then spacers to allow you to tighten the arbor nut to secure the bell clamp to the lathe. Position the tool bit in the left hand of the rotor truer so you can machine the face of the bell clamp. Machine the face of the bell clamp taking just enough off of it to cut the full face of the clamp the full 360 degrees. Before you loosen the arbor nut, match mark the hub of the bell clamp to the arbor and line up these marks before machining a rotor. A magic marker can be used to make the match marks. Machine a rotor and recheck the calibration. Repeat this procedure on all Inside Bell Clamps used.

Important: If runout is still present, contact the brake lathe supplier.

ON-CAR TYPE LATHE

Use the following procedure to calibrate an On-Car brake lathe:

1. Connect the lathe to a vehicle using the appropriate adapter.
2. Attach a vise-grip dial indicator to a fixed point in the wheel well and bring the dial indicator to a flat surface on the cutting head.
3. Turn on the lathe and press the "start" button so the lathe begins to compensate.
4. Once compensation is complete, note the runout as measured by the dial indicator. Measured runout at this point is overstated given that it is outside the rotor diameter.
5. If runout is in excess of 0.1016 mm (0.004 in) (0.050 mm (0.002 in) as measured within the rotor diameter), calibration must be tightened. Follow manufacturer's instructions for tightening the calibration of the lathe. This information is found in the manual supplied with the lathe.

Important: If the machine is taking a long time to compensate during normal use, prior to checking the lathe calibration, it is recommended that the machine be disconnected from the adapter and the adapter (still connected to the vehicle) is rotated 180 degrees and the machine reattached. This will accomplish two things:

The following information has been added as a reference to ensure your Pro-Cut PFM lathe provides a consistent smooth surface finish over long term usage.

Cutting Tips/Depth of Cut/Tip Life

The cutting tips must be right side up. Reference marks always face up. The cutting tips may not have chips or dings in the surface of the points. Cuts of 0.1016-0.381 mm (0.004-0.015 in) will provide the best surface finish and the optimal tip life. When cleaning or rotating the cutting bits, make sure that the seat area for the tip on the tool is free and clear of debris.

Cutting Head

On each brake job, the technician must center the cutting head for that particular vehicle using one of the mounting bolt holes on the slide plate. Once the head is centered, it is vital that the technician use one hand to push the head firmly and squarely back into the dovetail on the slide plate while using the other hand to tighten the Allen-Hex bolt that secures the head. Failure to do this could result in chatter occurring during the cut.

Tool Holder Plate (Cutting Head)

The tool holder plate is the plate that the cutting arms are attached to. It can bend or break if a technician accidently runs the cutting arms into the hub of the rotor while the rotor is turning. Cuts of more than 0.508 mm (0.020 in) can also bend this plate. Once bent, the lathe will most likely not cut properly until the tool holder plate is replaced. In order to verify the condition of the tool holder plate on a machine that will not cut right, remove the mounting bolt and remove the cutting head from the slide plate. With the cutting head titled at an angle, lay the long edge of the tool holder plate down on the flat part of the slide plate. If any gap can be seen between the edge and the slide plate, the tool holder plate is bent and the source of vibration. Also check to ensure that the cutting arms are lying flat on the upper side of the tool holder plate. If the mounting arm post is bent, it will show itself by having the back of the cutting arm lifting off the surface of the tool holder.

Gib Adjustment/Loose Gib

As wear occurs between the slide plate and the box it rides on, you must take up the slack. You do this by way of a moveable wedge, which we call the gib. Your lathe manual details the adjustment process, which you should perform when required after monthly checks or whenever surface finish is inconsistent.

Brake pulsation is caused by brake rotor thickness variation. Brake rotor thickness variation causes the piston in the brake caliper, when applied, to "pump" in and out of the caliper housing. The "pumping" effect is transmitted hydraulically to the brake pedal. Brake pulsation concerns may result from two basic conditions:

1. Thickness Variation Pulsation is Caused by Lateral Run Out (LRO). -- LRO on a brake corner assembly is virtually undetectable unless measured (with a dial indicator after the brake service) and will not be detected as brake pulsation during an after brake service test drive. If the brake corner is assembled with excessive LRO (greater than 0.050 mm (0.002 in), thickness variation will develop on the brake rotor over time and miles. Excessive LRO will cause the brake pads to wear the brake rotors unevenly, which causes rotor thickness variation. Pulsation that is the result of excessive Lateral Run Out usually develops in 4,800 - 16,000 km (3,000 - 10,000 mi). The more excessive the LRO, the faster the pulsation will develop. LRO can also be induced when uneven torque is applied to wheel nuts (lug nuts). Improper wheel tightening after tire rotation, spare tire usage, brake inspection, etc. can be the cause of brake pulsation. Again, it usually takes 4,800 - 16,000 km (3,000 - 10,000 mi) AFTER the service event for the condition to develop. The customer does not usually make the connection between the service event and the awareness of the pulsation. The proper usage of torque wrenches and/or torque sticks (torque limiting sockets) will greatly reduce or eliminate the pulsation conditions after wheel service events. The improper use of impact wrenches on wheel nuts greatly increases the likelihood of pulsation after wheel service.

The following are examples of pulsation conditions and reimbursement recommendations:

•	If the customer noticed the condition between 4,800 - 16,000 km (3,000 - 10,000 mi) and it gradually got worse, normally the repair would be covered. The customer may tolerate the condition until it becomes very apparent.

-	If a GM dealer performed a prior brake service, consider paying for the repair and then strongly reinforce after brake rotor service LRO measurement and correction of excessive LRO using Brake Align.

-	If the customer had the brake service done outside of a GM dealership, normally GM would not offer any assistance.

•	If a customer indicated they had wheel service, ask who performed the service. Then;

-	If a GM dealer performed the service, consider paying for the repair and then strongly reinforce the use of torque sticks at the dealer. Two common size torque sticks cover 90% of all GM products. Each technician needs to use torque sticks properly every time the wheel nuts are tightened.

-	If the customer had the wheel service done outside of a GM dealership, normally GM would not offer any assistance.

2. Thickness Variation Caused by Brake Rotor Corrosion -- Rotor corrosion is another form of thickness variation, which can cause a pulsation concern and can be addressed as follows:

•	Cosmetic Corrosion:

•	In most instances, rotor corrosion is cosmetic and refinishing the rotor is unnecessary.

•	Corrosion -- Pulsation Caused by Thickness Variation (Lot Rot/Low Miles -- 0-321 km (0-200 mi):

•

At times more extensive corrosion can cause pulsation due to thickness variation. This usually happens when the vehicle is parked for long periods of time in humid type conditions and the braking surface area under the pads corrodes at a different rate compared to the rest of the braking surface area. Cleaning up of braking surfaces (burnishing) can be accomplished by 10-15 moderate stops from 56-64 km/h (35-40 mph) with cooling time between stops. If multiple moderate braking stops do not correct this condition, follow the "Brake Rotor Clean-Up Procedure" below.

•	Corrosion -- Pulsation Caused by Thickness Variation (without rotor flaking/higher mileage -- 3,200-8,000 km (2,000-5,000 mi):

•

In some cases, more extensive corrosion that is not cleaned up by the brake pad over time and miles can cause the same type of pulsation complaint due to thickness variation. In these cases, the rotor surface is usually darker instead of shiny and a brake pad foot print can be seen against the darker surface. This darker surface is usually due to build-up, on the rotor material surface, caused by a combination of corrosion, pad material and heat. To correct this condition, follow the "Brake Rotor Clean-up Procedure" below.

•	Corrosion -- Pulsation Caused by Thickness Variation (with rotor flaking/higher mileage -- 8,000+ km (5,000+ miles):

•

At times, more extensive corrosion over time and miles can cause pulsation due to thickness variation (flaking). This flaking is usually a build up, mostly on the rotor material surface, caused by a combination of corrosion, pad material and heat. When rotor measurements are taken, the low areas are usually close to the original rotor thickness (new rotor) measurement and the high areas usually measure more than the original rotor thickness (new rotor) measurement (depending on mileage and normal wear). To correct this condition, follow the "Brake Rotor Clean-up Procedure" described below.

Important: In some flaking instances, cleaning-up this type of corrosion may require more rotor material to be removed then desired. Customer consideration should be taken in these situations and handled on a case by case basis, depending on the amount/percentage of rotor life remaining and the vehicle's warranty time and miles.

Clean-up the rotors on an approved, well-maintained brake lathe to guarantee smooth, flat and parallel surfaces. Check for clean and true lathe adapters and make sure the arbor shoulder is clean and free of debris or burrs. For more information see the "Brake Lathe Calibration Procedure" section in this bulletin.

1. On the outboard area of the rotor, position the cutting tools one-eighth of an inch into the brake pad area of the rotor. Feed the cutting tools into the rotor until they cut the rotor to new metal, a full 360 degrees. Zero each dial and back off a full turn.
2. Move the cutting bits to the middle of the rotor and do the same procedure. If zero is passed during the process, reset zero. Back off a full turn.
3. Position the cutting bits one-eighth of an inch inside the inboard (closest to the hub) edge of the brake pad contact area. Do the same procedure. If zero is passed during the process, reset zero.
4. Back off a full turn and position the cutting bits all the way inboard in preparation to refinish the full rotor surface. Advance both tool cutters to the zero setting plus just enough to clean up the entire rotor surface.
5. After completing the refinish, sand both sides of the rotor for approximately one minute per side using a sanding block and 130-150 grit sandpaper to obtain a non-directional finish.

Important: Only remove the necessary amount of material from each side of the rotor and note that equal amounts of material do not have to be removed from both sides on any brake system using a floating caliper.

Important: In many of these instances, such a minimal amount of material is removed from the rotor that customer satisfaction is not a concern for future brake services. This procedure is intended to "Clean-up" the rotor surface and should be conveyed to the customer as such - not as "cut", "refinish" or "machine", which tends to be terms understood as a substantial reduction of rotor material/life. If the brake lathe equipment being used is not capable of removing minor amounts of material while holding tolerances, further lathe maintenance, repair, updates or equipment replacement may be necessary.

Some brake noise is normal and differences in loading, type of driving, or driving style can make a difference in brake wear on the same make and model. Depending on weather conditions, driving patterns and the local environment, brake noise may become more or less apparent. Verify all metal-to-metal contact areas between pads, pad guides, caliper and knuckles are clean and lubricated with a thin layer of high temperature silicone grease. Brake noise is caused by a "slip-stick" vibration of brake components. While intermittent brake noise may be normal, performing 3 -4 aggressive stops may temporarily reduce or eliminate most brake squeal. If the noise persists, a brake dampening compound may be applied to the back of each pad. This allows parts to slide freely and not vibrate when moving relative to each other. Use Silicone Brake Lubricant, ACDelco P/N 88862181 (Canadian P/N 88862496) or equivalent.

The following noises are characteristics of all braking systems and are unavoidable. They may not indicate improper operation of the brake system.

Squeak/Squeal Noise:

Grinding Noise:

Groan Noise:

A groan type noise may be heard when stopping quickly or moving forward slowly from a complete stop. This is normal. On vehicles equipped with ABS, a groan or moan type noise during hard braking applications or loose gravel, wet or icy road conditions is a normal function of the ABS activation.

Brake Rotors:

Brake Pads:

Brake Wear:

Several factors impact brake lining wear and should be taken into account when reviewing related issues:

-- heavy loads/high temperatures/towing/mountainous driving/city driving/aggressive driving/driver braking characteristics (left foot or two feet)

The following are conditions that may extend brake lining wear:

-- light loads/highway driving/conservative driving/level terrain

Refer to Corporate Bulletin Number 01-05-23-001A for the Brake Align® application chart.

For vehicles repaired under warranty, Brake Align® Run-Out Correction Plates should be documented in technician comments of the warranty claim and the cost of the plates submitted as a Net Amount (net item code "M") at cost plus 40%.

Brake Align® Run-Out correction Plates are available through the following suppliers:

* We believe this source and their products to be reliable. There may be additional manufacturers of such products. General Motors does not endorse, indicate any preference for or assume any responsibility for the products from this firm or for any such items, which may be available from other sources.

Important: 

For vehicles repaired under warranty, use: