1ST & 2ND SHIFT SHUDDER NEW PISTON & RING ASSY.

TRANSMISSION APPLICATIONS: SUBJECT: 1991 HYDRA-MATIC 4L80E/4L80-EHD 1-2 SHIFT SHUDDER HARSH OR (MT1) DOUBLE FEEL (NEW PISTON AND RING 1990 HYDRA-MATIC 3L80/3L80-HD M40 PKG

TRANSMISSION MODELS: VEHICLE APPLICATIONS: ALL MODELS C/K,R/V AND P TRUCKS G-VAN

Service Information:

Some HYDRA-MATIC 4L80-E/4L80-EHD and 3L80/3L80-EHD transmissions may experience a 1-2 shift shudder or harsh double feel. This is caused by fluid leaking past the rear accumulator piston seals. A new piston and ring assembly package was released that eliminates this condition.

Date of Production Change: Refer to Figure 1 -------------------------- Starting April 18,1991 (Julian Date 108) all HYDRA-MATIC 4L80-E/ 4L80-EHD models were built with the new Accumulator Piston and Seals.

Service Parts Information: Refer to Figure 2 --------------------------

Part Number Part Name ----------- ------------------ 8680929 Piston and Ring Assembly, Rear Accumulator

New Piston and Ring Assembly can be used with older model cases. When installing, use TRANSJEL J36850 or equivalent to aid in assembly.

Old Piston Ring and Ring Assembly cannot be used on new cases.

Service Manual Reference:

Refer to the On-Vehicle Section of the appropriate service manual for proper replacement procedures.

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.