RATTLE AFTER TCC LOCK-UP REPLACE TORQUE CONVERTER

SUBJECT: TORSIONAL RATTLE AFTER TORQUE CONVERSION CLUTCH LOCKUP

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

Owners of some 1991-1992 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.

Once the condition is created if the rattle/vibration stops when:

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

2. The vehicle downshifts to 3rd gear

The Torque Converter must be replaced with a revised Torque Converter (P/N 08686969).

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

Use applicable labor time guide for labor hours.

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.