For 1990-2009 cars

# HARSH 1-2 UPSHIFT INSTALL SERVICE PACKAGE

#### SUBJECT: HARSH 1-2 UPSHIFT (INSTALL SERVICE PACKAGE)

#### MODELS AFFECTED: 1992 FIREBIRD MODELS WITH 4L60 TRANSMISSION TRANSMISSION MODELS: 2FTM, 2FUM, 2FZM

CONDITION: (Figure 1): ---------------------- Some vehicles equipped with a 1992 HYDRA-MATIC 4L60 transmission built between Julian Date 061 (March 1, 1992) and Julian Date 171 (June 19, 1992) may experience a harsh 1-2 upshift.

#### NOTE: Once the transmission is brought to operating temperature, the condition may not be able to be reproduced until a "cold soak" (overnight) is performed.

#### CAUSE:

------ The above condition may be caused due to a tapered 1-2 accumulator sleeve. The tapered bore may cause the 1-2 accumulator valve to stick in the bottom of the bore.

CORRECTION: (Figure 2) ---------------------- To improve the 1-2 shift, install the service package listed in this bulletin. A 1-2 accumulator valve and 1-2 accumulator valve sleeve (which, normally, is not serviceable) is included in the package.

#### SERVICE PARTS INFORMATION:

Package Number Transmission Models ------- ------------------- 8687992 2FTM, 2FUM, 8688900 2FZM,

Parts are currently available from GMSPO.

#### SERVICE MANUAL REFERENCE:

Refer to the Hydra-Matic 4L60 unit repair section of the appropriate Service Manual for repair information.

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.