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

SUBJECT: 1-2 SHIFT SHUDDER, HARSH OR DOUBLE FEEL (NEW PISTON AND RING SERVICE PACKAGE-ASSEMBLY)

MODELS: 1991 C/K AND R/V/G/P W/ 4L80E AND 1990 C/K AND R/V/G/P WITH 3L80

Some 1990 C/K and R/V/G/P trucks with HYDRA-MATIC 3L80 transmissions and 1991 C/K and R/V/G/P trucks with 4L80-E 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. Refer to the on-vehicle section of the appropriate service manual for proper replacement procedures.

Date of Production Change: (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.

PARTS INFORMATION: (Figure 2) ----------------------------- Part Part Name Number --------- ------------------------ 8680929 Piston and Ring Assembly, Rear Accumulator

New Piston and Ring Assembly can be used with older model cases. When installing, use TRAN-SJEL J36850 or equivalent to aid in assembly. Old Piston Ring and Ring Assembly cannot be used on new cases.

Parts are currently available from GMSPO.

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.