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

1-2 SHIFT DURING COLD WEATHER - SERVICE AND PARTS INFORMATION ON NEW 1-2 ACCUMULATOR PISTON

MODELS AFFECTED: 1988 SKYHAWKS, SKYLARKS, AND CENTURYS ---------------- EQUIPPED WITH A THM 125C (MD9) TRANSAXLE

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 Bulletin 87-7125-5 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 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 bu-ilt 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.

NOTICE: 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.