NO ENGINE BRAKING IN DRIVE NEW PISTON-FRONT ACCUMULATOR

Model and Year: 1978-88 TRUCKS WITH THM 400/475

This bulletin covers no engine braking in Drive 2 (D2) selector range caused by a broken plastic Front Accumulator Piston (303). The transmissions affected are the THM 400/475/ HYDRA-MATIC 3L80/3L80-HD Transmission. The die cast aluminum piston can be used in service for this condition and will reduce the chance of any broken or cracked pistons.

DATE OF PRODUCTION CHANGE: (Figure 1) -------------------------

August 1, 1988 (Julian Date 214) all 1989 THM 400/475/ HYDRA-MATIC 3L80/3L80-HD Transmissions were built with the aluminum Front Accumulator Piston (303).

SERVICE PARTS INFORMATION: (Figure 2) -------------------------

Service Part No. Part Description

8626883 Piston-Front Accumulator (303)

This part is currently available from GMSPO.

IMPORTANT: The plastic Front Accumulator Piston (8629080) should be replaced if found in any 1978-88 Control Valve Assembly (049).

SERVICE MANUAL REFERENCE:

Refer to the Unit Repair Section of the appropriate Service Manual for proper replacement procedure.

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.