For 1990-2009 cars

# HARSH UPSHIFTS AT HIGH ALTITUDES

#### VEHICLES AFFECTED: 1985-86 'A' Models Equipped With 2.8L Engine and 440-T4 Transaxle

This bulletin applies only to the following 440-T4 models: CW, CP, HT, CM, CN, HJ, HA, CFH, CMH, CNH, HJH, HBH.

Some 1985 through 1986 'A' models equipped with a 2.8L engine and a THM 440-T4 transaxle may exhibit harsh upshifts when operated at high altitudes. This condition may be caused by excessive line pressure resulting from insufficient engine vacuum. Refer to Figure 1 for transaxle identification information.

A new vacuum modulator assembly and modulator valve* have been released for service in a package (Part Number 8646956) for the harsh upshifts condition. The package consists of:

- Transaxle Vacuum Modulator Assembly - Modulator valve - O-Ring Seal - Instruction Sheet

* Note: A new engine vacuum line (Part Number 14052624) must be installed with the service package.

Refer to the appropriate Service Manual for removal and installation procedures as well as to Figure 2 for correct modulator valve orientation.

The service package ONLY applies to the following THM 440-T4 models:

1985 Models 1985-1/2 Models 1986 Models ----------- --------------- ----------- CW CM CFH CP CN CMH HT HJ CNH HA HJH HBH

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.