REAR UNDERBODY NOISE DIAGNOSIS CONDITIONS & CORRECTIONS

Model and Year: 1990 W CAR

Some 1990 W-cars may exhibit various noises emanating from the rear of the vehicle that may be caused by a variety of conditions in the rear suspension, exhaust, fuel or park brake cable systems.

It is the intent of this bulletin to summarize prior issued bulletins and provide insight into other conditions that have been noted to aid in the proper diagnosing of customer noise comments.

When prior published bulletins are referenced, they should be utilized to insure proper service procedures are followed.

SQUEAK/SQUAWK NOISE

Condition: Squeaking during normal suspension/vehicle operation.

Cause: Park brake cable movement through grommet in cable support brackets.

Correction: Apply lubricant to cables in area of grommets. Reference Dealer Service Bulletin No. 90-90-5, dated November 1989.

Condition: Squawking during normal vehicle operation and most prevalent in cold or wet weather.

Cause: Auxiliary spring rubbing against edge of spring mounting bracket.

Correction: Remove auxiliary spring per procedure outlined in Service Manual and reinstall with clearance to edge of mounting brackets.

CLUNK NOISE

Condition: Clunk noted during normal suspension/vehicle movements.

Cause: Exhaust system contacting rear stabilizer bar.

Correction: Inspect exhaust system and stabilizer bar for witness marks due to metal to metal contact. Align exhaust system to provide adequate clearance if interference condition is noted.

RATTLE NOISE

Condition: Metallic rattling during normal vehicle operation or engine run up in neutral.

Cause: Loose clinch nuts in either exhaust intermediate pipe or underbody hanger brackets.

Correction: Install washer P/N 11500367 between hanger and either or both the underbody and pipe brackets.

Condition: Dull rattling noted during normal suspension/vehicle operation.

Cause: Park brake cable grommets not properly installed in underbody retaining brackets.

Correction: Insure both underbody brackets are not distorted and install cable grommets. Reference Dealer Service Bulletin No. 90-90-5, dated November 1989.

Condition: Metallic rattling noted during engine run-up in neutral or normal suspension/vehicle operation.

Cause: Loose exhaust system heat shields.

Correction: Inspect and tighten loose exhaust system heat shield fasteners insuring sufficient clearance is maintained.

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.