BRAKE PAD LIFE, BRAKE NOISE OR BRAKE PEDAL EFFORT

SUBJECT: BRAKE PAD LIFE, BRAKE NOISE, OR BRAKE PEDAL EFFORT (REPLACE PADS/INSPECT ROTOR THICKNESS)

VEHICLES AFFECTED: 1988-93 "W" MODEL

THIS BULLETIN SUPERSEDES AND REPLACES CORPORATE BULLETIN REFERENCE NUMBER 335003.** THIS BULLETIN IS BEING REVISED TO ADD DIVISIONAL BULLETIN REFERENCE NUMBERS TO CORPORATE BULLETIN REFERENCE NUMBER 135012R**. AND CORPORATE BULLETIN REFERENCE NUMBER 135012R.**

CONDITION:

--------- Some owners of 1988-93 W-cars may express concem with:

1. Brake Noise 2. Brake Pad Life 3. Brake Pedal Feel/Effort

CAUSE:

----- These vehicles are equipped with 4-wheel disc brakes. Some light brake squeal is NORMAL. 4-wheel disc brakes also typically have a firmer pedal feel. A cause for pedal effort or lining life concerns could be improper rotor finish. If the vehicle has had brake service which included rotor turning, that may be the cause.

CORRECTION:

---------- A. Pads

Increased pad life AND lower pedal effort may be obtained by replacing both the front and rear original pads with the new 1993 pads.

Front Lining P/N 12510029 Rear Lining P/N 12510030

Note: SOME BRAKE SQUEAL IS NORMAL

While the 1993 pads may result in an increase in pad life, and lower pedal effort and better feel, they may also be associated with higher levels of brake squeal at the beginning of brake apply ("Tip-IN" squeal), or at the end of brake apply ("Pinch-Out" squeal).

For servicing a vehicle where pedal feel/effort, rather than pad life is the primary concern, GMSPO will still carry the linings listed below. These linings are more aggressive and will reduce pedal effort even more. But, owners should be told that some "GRINDING/GROWLING" type noise is to be expected from these and IS NORMAL. DO NOT USE AS A GENERAL REPLACEMENT PART.

o Front Lining P/N 18019507 o Rear Lining P/N 18019508

RECOMMENDED SERVICE BRAKE SQUEAL

DO NOT TURN ROTORS OR SAND PADS FOR BRAKE NOISE CONCERNS.

While this may temporarily reduce some brake squeal, it may also reduce brake effectiveness and/or pad life.

BRAKE SQUEAL is caused by vibration of brake components. Some intermitent brake squeal is NORMAL. Usually 3-4 aggressive stops will temporarily reduce or eliminate most brake squeal. If this does not work, remove, index (rotate wheel one (1) wheel bolt), and remount the wheels and make sure the wheel nuts are torqued in the STAR PATTERN to specification.

If the noise persists, a brake dampening compound may be applied to the back of each pad. Use Permatex Disc Brake Quiet #126hb or equivalent.

B. Front Rotors

DO NOT TURN ROTORS FOR THE FOLLOWING:

o Pad Replacement o Brake Noise o Pedal Effort/Feel

Rotors should only be tumed for:

o Pulsation Concerns o Heavy Scoring - In Excess of .060" (1.5 mm)

If the front rotors on a high-pedal-effort vehicle have been previously turned, they should be replaced. It is not always apparent with visual inspection whether a rotor has been turned. Rotor thickness should be measured with a micrometer. The thickness of a new rotor is 1.040" (26.4 mm). If a rotor measures 1.025" (26.0 mm) or less, on a vehicle with comments of pedal efforts, the rotor probably has been turned and should be replaced.

C. Rear Brakes

Also, the rear calipers should be inspected for caliper slide force. When the caliper is removed for pad replacement, try to move each sleeve with both thumbs pushing on the end of the sleeve. If one sleeve is found that won't slide, refer to Service Bulletin 135011 for the procedure to service the rear caliper sleeves. If one caliper has a sticking sleeve, both calipers should be serviced with this procedure.

For vehicles repaired under warranty use:

Labour Operation: H0042 Front H0043 Rear

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.