Message Date: 12/20/99 Admin Number: VSG19990282
Dealership cc: Service Manager, Warranty Administrator (Recommended Distribution)
Revision Release Date: 12/20/99
To (Dealer): All Chevrolet, Oldsmobile and
The previous Admin Number:VSG19990275 inadvertently didn't have the makes andmodels for this posting..
The makes and models are as follows:
This letter outlines GM's procedures and guidelines for brake rotor service forthe above listed GM vehicles.
Pulsation is caused by brake rotor thickness variation. Thickness variation ofthe rotor causes the piston in the brake caliper to "pump" in and out of the caliper housing. This "pumping" effect is transmitted hydraulically to the brake pedal.
Improper wheel tightening after tire rotation, spare tire usage, brakeinspection, etc. can be the cause of pulsation. It usually takes 3000-7000 miles after this event for the problem to surface. The owner or driver doesn't usually make the connection between the service event and the awareness of the pulsation.
The improper use of impact wrenches on wheel nuts greatly increases thelikelihood of pulsation after wheel service. A torque limiting socket or torque wrench must be used to insure that the wheel nuts are tightened to specification. This should be done in 3 steps (snug, half torque and full torque) using the star pattern. Never use lubricants or penetrating fluids on wheel studs, nuts, or mounting surfaces. Wheel nuts, studs, and mounting surfaces must be clean and dry.
Customer assistance concerning brake pulsation and brake wear should always takeinto account the individual circumstances on a case by case basis. Remember that customer satisfaction is critical to GM and that often it is in GM's best interest to satisfy and educate the customer concerning future brake service.
EXPLANATION OF BRAKE ROTOR WARRANTY SERVICE PROCEDURE
2. Installation of new rotors does not necessarily
require pad replacement.
3. When installing new rotors, do not reface them. Original equipment rotorsurfaces are ground to ensure smooth finish and parallelism between mounting and friction surfaces. New rotors should not be resurfaced before installation.
BRAKE SERVICE TECHNIQUES
2. Clean and lube slide pins.
3. Ensure bearing flanges and rotor mounting surfaces are free of corrosionwhen installing rotors to prevent inducing lateral runout. Use Kent Moore tool J42450 to clean the corrosion around the wheel studs.
4. Install the new rotors.
5. A torque limiting socket or torque wrench must be used to insure that thewheel nuts are tightened to specification. This should be done in 3 steps (snug, half torque and full torque) using the star pattern. Never use lubricants or penetrating fluids on wheel studs, nuts, or mounting surfaces. Wheel nuts, studs, and mounting surfaces must be clean and dry.
LIGHTLY RUSTED ROTORS
FACTS ABOUT BRAKE NOISE
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