HARSH 1-2 UPSHIFT UPDATE CALIBRATION

Subject: HARSH 1-2 UPSHIFT

Model and Year: 1991 CAPRICE WITH 5.OL ENGINE AND 4L60 TRANSMISSION

BULLETIN COVERS:

Some 1991 Chevrolet Caprice vehicles equipped with HYDRA-MATIC 4L60 transmissions and 5.0 liter engines may have a harsh 1-2 upshift. A calibration change has been made to soften the 1-2 shift.

SERVICE INFORMATION:

To soften the 1-2 shift, install the service package listed in this bulletin. A 1-2 accumulator valve spring (which is not normally serviceable) is included in the package for those technicians who are familiar with control valve disassembly and reassembly. If you do not wish to service the control valve assembly, you may order a complete replacement control valve assembly from the GMSPO catalog.

DATE OF PRODUCTION CHANGE:

Beginning May 7, 1990 (Julian Date 127) all 1 BBM models were built using the revised calibration.

SERVICE PARTS INFORMATION:

Description Part

SERVICE PACKAGE - HARSH 1-2 8673944 (reverse boost valve and sleeve, 1-2 accumulator valve spring, 1-2 accumulator piston spring, spacer plate)

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.