RATTLE AFTER TCC LOCK-UP REPLACE TORQUE CONVERTER

SUBJECT: TORSIONAL RATTLE AFTER TORQUE CONV. LOCKUP (REPLACE TORQUE CONVERTER)

MODELS: 1991-92 S-TRUCKS WITH 2.5L ENGINE (L38) AND 4L60 AUTOMATIC TRANSMISSION

Owners of some 1991-92 S-trucks with 2.5L engines (RPO L38) and automatic transmissions (4L60) may experience a torsional rattle noise after the Torque Converter Clutch locks up. The condition is usually in the 45-55 mph range and when under light acceleration.

The torsional rattle may be due to incorrect spring rate on the damper springs in the torque converter. The result is a bottoming-out condition in the torque converter damper assembly.

Torsional rattle occurs under the following condition:

1. Vehicle must be in 4th gear.

2. The torque converter clutch must be locked in.

3. The Vehicle speed must be between 45-55 MPH.

4. The Vehicle is under a light acceleration.

The Torque Converter must be replaced with a revised Torque Converter (P/N 08686969), if the rattle/vibration stops when:

1. Light brake application is made (To unlock the TCC), OR

2. The vehicle downshifts to 3rd gear.

VEHICLES INVOLVED

Identification of vehicles can be made by noting the Julian date on the 4L60 automatic transmission. Vehicles with Julian date AFTER 086 are NOT affected.

SERVICE PARTS INFORMATION

Part Number Description

08686969 Torque Converter

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: K7020

Labor Time: 2.9 hrs.

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.