1-1 SHIFT DURING COLD WEATHER NEW ACCUMULATOR PISTON - P/N

Model and Year: 1988 CELEBRITY, CAVALIER, CORSICA, BERETTA WITH THM 125/125C TRANSAXLE

This bulletin covers a New 1-2 Accumulator Piston (421) and Seal (420) for vehicles equipped with a THM 125C transaxle to increase shift consistency during vehicle operation in cold weather conditions. The groove bottom on the 1-2 accumulator piston where the seal is located is flat and the new piston seal is now made of a soft rubber instead of a hard P.T.F.E. material. (Refer to Figure 2)

Some vehicles equipped with a 1987 THM 125C built between the dates of April 13, 1987 through April 21, 1987 (Julian Dates 103-112), may have a rolled or misassembled 1-2 accumulator piston seal, resulting in a possible harsh 1-2 shift. This piston seal has a resemblance to the new (rubber) seal (420). Refer to Chevrolet Dealer Service Bulletin Number 87-231, Section 7A, for additional information. If replacement of this seal built between April 13, 1987 through April 21, 1987 (Julian Dates 103-112) is necessary, the new 1-2 Accumulator Piston (421) and Seal (420) must be used.

DATE OF PRODUCTION CHANGE: (Refer to Figure 1)

May 18, 1988 (Julian Date 139) the new 1-2 Accumulator Piston and Seal went into production for all Willow Run built THM 125/125C transaxles. Future production changes are scheduled for S.O.P. 89 for Windsor built THM 125/125C transaxles.

SERVICE ACTION: (Refer to Figure 2)

The new 1-2 Accumulator Piston and Seal can be used on any 1980 through 1988 THM 125C transaxle as a complete assembly. The previous 1-2 Accumulator Piston is no longer available for service use. If replacement of the 1-2 Accumulator Piston seal is necessary, use the following guidelines:

o The new seal must be used with the new piston.

o The previous seal must be used with the previous piston.

NOTE: Do not attempt to mix parts or delayed and extended shift conditions will occur.

SERVICE PARTS INFORMATION:

When ordering parts to service the 1-2 Accumulator Assembly, use the following part numbers:

Package No. Description

8665920 Package 1-2 Accumulator Piston (421) and Seal (420) 8665807 Seal 1-2 Accumulator (Rubber) (420) 8631895 Seal 1-2 Accumulator (P.T.F.E.)

SERVICE MANUAL REFERENCE:

Refer to the THM 125 (MD9) Automatic Transaxle Unit Repair section of your service manual whenever replacement of the 1-2 Accumulator Piston and Seal is necessary.

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.