Some 1987-1988 DeVilles, Fleetwoods, Eldorados, and Sevilles equipped with the THM 440-T4 built prior to November 24, 1987 (Julian Date 328), may experience a harsh engagement condition when shifting from park/neutral to drive/reverse.
This condition may be caused by miscalibrated 1-2 and reverse servo cushion springs. Before proceeding with repair, verify that line pressures are within specification. Refer to the appropriate Service Information Manual for line pressure specification and repair procedures for high line pressures.
If line pressures are within specification, repair this condition by installing a new 1-2 servo cushion spring (for harsh engagement into dr ive) or a new reverse servo cushion spring (for harsh engagement into reverse) using the following procedure:
1. Remove the 1-2 servo assembly and the reverse servo assembly from the transaxle. Refer to the appropriate Service Information Manual, Section 7Al 440-T4 Diagnosis and On-Car Service.
2. Disassemble and Replace the 1-2 servo cushion spring (559), P/N 8668123, and the reverse servo cushion spring (549), PN 8668121, (refer to Figure 1).
3. Install the 1-2 servo assembly and the reverse servo assembly in the transaxle.
If a harsh engagement condition is still evident after performing this procedure, refer to harsh engagement diagnostic procedures in the appropriate Service Information Manual. For warranty purposes, use Labor Operation T6279 at 1.3 hours for Eldorados and Sevilles, and 1.6 hours for DeVilles and Fleetwoods.
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.