The previous Admin Number:VSG19990275 inadvertently didn't have the makes and models for this posting..

This letter outlines GM's procedures and guidelines for brake rotor service for the above listed GM vehicles.

PULSATION
Brake pulsation is often caused by factors outside customer control. In these instances the repair is covered under the GM New Car Bumper to Bumper Warranty.

Pulsation is caused by brake rotor thickness variation. Thickness variation of the 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, brake inspection, 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 the likelihood 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 take into 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
1. If a customer with a vehicle listed above complains of brake pulsation, verify the concern. If the brakes pulsate, replace both front brake rotors with part number 18060442.

3. When installing new rotors, do not reface them. Original equipment rotor surfaces are ground to ensure smooth finish and parallelism between mounting and friction surfaces. New rotors should not be resurfaced before installation.

BRAKE SERVICE TECHNIQUES
1. Clean and lube all metal-to-metal contact points (i.e.; caliper to knuckle, pad to knuckle, etc.).

3. Ensure bearing flanges and rotor mounting surfaces are free of corrosion when installing rotors to prevent inducing lateral runout. Use Kent Moore tool J42450 to clean the corrosion around the wheel studs.

5. 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.

LIGHTLY RUSTED ROTORS
Light surface rust on rotor braking surfaces is often cosmetic and can be eliminated during a few normal driving stops. Rusting may occur when a vehicle is not driven for extended periods. Rotors with surface rust on unsold new cars can usually be burnished clean by performing 15 moderate stops from 35-40 mph (62-75 km/h) with cooling time between stops.

FACTS ABOUT BRAKE NOISE
Some brake noise is normal and differences in loading, type of driving, or driving style can make a difference in brake wear and brake noise on the same make and model. Depending on weather conditions, driving patterns, and the local environment, brake noise may become more or less apparent. Please refer to your service manual for appropriate information on brake noise.