CLUTCH CHATTER/SHUDDER ON LAUNCH-NEW DESIGN CLUTCH ASSY.

Subject: CLUTCH CHATTER/SHUDDER ON LAUNCH

Model and Year: 1988-91 C/K TRUCKS WITH 4.3L OR 5.0L ENGINES AND 4-SPEED OR 5-SPEED MANUAL TRANSMISSION

Some 1988-91 C/K trucks equipped with 4.3L or 5.0L engines with 4-speed or 5-speed manual transmissions may experience a condition of chatter or shudder on launch.

Revised clutch discs and matching pressure plates have been released for these vehicles and are available through GMSPO. The clutch discs feature a revised facing material which will provide smoother engagement and increased wear resistance. These revised discs can be identified by the name stamp Valeo while the previous discs were stamped Borg Warner. The pressure plates have been revised to work with the discs and must be replaced at the same time. The revised pressure plates will be marked with the name stamp Luk while the previous pressure plate may be marked with the name stamp Luk or Borg Warner.

The installation of these parts will provide significant improvement in the involved vehicles.

VEHICLES INVOLVED

Some 1988-91 C/K trucks equipped with 4.3L or 5.0L engines and 4-speed or 5-speed transmissions built prior to the following VIN breakpoints:

4.3L / 5.0L Fort Wayne (Z) MZ159936 Oshawa (1) M1178933 Pontiac (E) ME152577

SERVICE PROCEDURE

The pressure plate and clutch disc should be replaced at the same time as the parts have been designed to work together. Refer to section 7C of the appropriate service manual for clutch disc and pressure plate replacement procedure.

IMPORTANT: Before removing the existing pressure plate, note the location of the paint dab on the pressure plate cover. This paint dab indicates the heavy side of the pressure plate assembly and is aligned with the light side of the engine at the assembly plant. The new pressure plate should be installed with the paint dab in the same location to preserve the balance of the engine assembly.

SERVICE PARTS INFORMATION

PRESSURE CLUTCH ENGINE TRANSMISSION PLATE P/N DISC P/N ------ ------------- --------- --------- 4.3L 4 or 5 SPEED 15668537 15668527 5.0L 5 SPEED 15668537 15668527

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation Models

K0800 C1 C2 C3

K0800 K1 K2 K3

Add K1 K2 K3 with skid plate

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.