GM Brake Service Procedure

GM BRAKE SERVICE PROCEDURE

1. Remove the wheel and caliper.

2. Measure rotor thickness. In order to determine if the rotor can be refinished, do the following 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.
1. Remove the rotor(s).

2. Measure the rotor for original thickness using a brake micrometer. Multiple measure points should be taken and the lowest measurement should be recorded.

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 lowest ORIGINAL rotor thickness measurement on the repair order hard copy as noted in the "Repair 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(R).

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

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

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.

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

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. 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.

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.

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

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.

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.

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 Nm (25-30 lb ft) the nuts using equal torque. DO NOT use impact wrenches, 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.

4. Connect the lathe to the adapter, turn on the lathe and activate the computer to compensate for run-out in the hub.

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.

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.

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.

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.

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.

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 88862650 (Canadian P/N 88901247).

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 repair order hard copy. Refer to the "Repair Order Documentation - Rotor Refinish" section of this bulletin.

8. Setting up to measure for Lateral Run Out (LRO):

Important
Measuring for Lateral Run Out (LRO) (steps 8 - 15) is no longer required however, these steps are being left in the overall procedure as a good check to be performed in the case of a repeat pulsation complaint. If you are not checking for LRO, go to step 16.

Bench-Type Lathe

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

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.

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

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.

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.

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.

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

On-Car Type Lathe

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

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).

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.

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. If the Lateral Run Out (LRO) measurement is 0.050 mm (0.002 in) or LESS, no correction is necessary. Go to Step 15 if this is the first rotor completed. Go to Step 16 if this is the second rotor completed. If the LRO is GREATER than 0.050 mm (0.002 in), go to Step 12.

12. 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 torque specification, refinished rotor is source of LRO due to a lathe qualification issue - see "Brake Lathe Calibration Procedure").

Hubless Rotor

1. Remove the rotor and using the Brake Align(R) application chart (found in TSB 01-05-23-001B), 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(R)" kit or TSB 01-05-23-001B.

2. Align the V-notch of the selected Brake Align(R) 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(R) Correction Plates are not available for the vehicle being serviced, refer to SI Document - Brake Rotor Assembled Lateral Runout Correction for correcting LRO.

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

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

1. Measure the rotor thickness.

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

13. Use a Dial Indicator to measure the rotor to verify the LRO is within specification.

14. If using,

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

ON-CAR LATHE - You must remove 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.

15. Perform Steps 1 through 7 on the opposite side of the vehicle (steps 1-12, if performing LRO).

16. Reinstall the rotors on both sides of the vehicle and perform the following steps:

1. Reinstall the calipers and pads.

2. Pump the brakes to pressurize the calipers.

3. Remove the lug nuts/conical washers.

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.

17. Road test the vehicle to verify the repairs.