CLUNK NOISE ON BRAKE RELEASE OR SLAP; POP SOUND REPAIR

VEHICLES AFFECTED: 1990 M, L AND G VANS

Some customers may experience a condition described as a slapping, popping, or clunking sound on 1990 G or M/L vans when the brakes are released. This condition can occur when the rear brake shoes track along the machined grooves of the rear brake drums during brake apply and are pulled or "slapped" back into their normal position against the backing plate by the return springs during brake release.

IMPORTANT: This condition will not damage any of the brake components.

This is a low mileage condition, and usually will disappear after the first few thousand miles a vehicle is driven as the brake drums become burnished.

The best service correction for this condition is to refinish the brake drums to a specification of 100 micro-inches or lower.

The following lathe settings should be adhered to in order to achieve the required finish quality:

Use cutting tool insert designated SNG 434 (Square Negative Ground)

Tool Cross Feed Per Revolution: .25mm (.010")

Depth Of Cut Per Side: as required - not to exceed the maximum drum diameter specification.

IMPORTANT: Brake shoes should be lightly sanded using 240 grit emery paper to remove any groves and/or marks left by the rough drum surface.

WARRANTY INFORMATION:

For vehicles repaired under warranty use applicable Labour Operations and times as published in the 1990 Canadian Labour Time Guide.

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.