HARSH ENGAGE, DOUBLE BUMP OR SHUDDER-PARK/NEUTRAL-REVERSE

MODELS AFFECTED: 1984-90 CENTURY 1985-90 ELECTRA/PARK AVENUE 1986-90 LESABRE, RIVIERA 1988-90 REGAL, REATTA

THIS BULLETIN HAS BEEN REVISED TO ADD INFORMATION ABOUT THE RUBBER TORSIONAL DAMPER UNIT. SEE "IMPORTANT" UNDER "BULLETIN COVERS" AND THE FIRST SENTENCE OF "SERVICE PROCEDURE

THIS BULLETIN SUPERSEDES BULLETIN 87-7440-13 WHICH SHOULD NOW BE DISCARDED.

BULLETIN COVERS:

A new reverse band assembly that will help decrease harsh engagement, double "bump" or shudder from park or neutral to reverse in a vehicle equipped with a Hydra-Matic 4T60 (THM 440T4). The new reverse band assembly has new friction material that will help decrease reverse engagement concerns.

Reverse engagement concerns can be caused by "oxidized" fluid (the fluid may visually appear to be okay), "glazed" (overheated) reverse band assembly friction material and/or improper surface finish on the drum of the 2nd clutch housing.

IMPORTANT:

Harsh reverse engagement could also be caused by a worn or damaged rubber torsional damper unit (on models so equipped) that is incorporated as part of the right hand drive axle shaft. Refer to section 4D of the Service Manual.

SERVICE PROCEDURE:

Check engine idle speed, engine/transaxle mounts, rubber torsional damper unit for the right hand drive axle shaft (on models so equipped) and transaxle reverse line pressure following Service Manual procedures. If okay, replace the reverse band assembly and 2nd clutch housing drum and bushing assembly with the appropriate parts listed below in "Service Parts Information".

DATE OF PRODUCTION CHANGE:

Starting February 07, 1990 (Julian Date 038) all Hydra-Matic 4T60 (THM 440T4) transaxles will be built with the new reverse band assembly.

SERVICE PARTS INFORMATION:

Model Part Year Number Description

1984-90 8675152 Reverse Band Assembly

1987-90 8661912 2nd Clutch Housing Drum and Bushing Assembly (six plate)

1984-86 8668958 2nd Clutch Housing Drum and Bushing Assembly (five plate)

Parts are expected to be available for part number 8675152 on 06-15-90. Until then normal part orders will not be accepted by GMSPO. Only verifiable emergency VIP orders will be accepted. SPO will make every effort to obtain parts. All parts will be placed on 400 control to waive VIP surcharges. However, the part will be shipped premium transportation at dealer's expense. All other order types will be canceled as incorrectly ordered while the 400 control is in place.

Parts are currently available from GMSPO for part numbers 8661912 and 8668958.

SERVICE MANUAL REFERENCE:

Refer to the Hydra-Matic 4T60 (THM 440T4) Automatic Transaxle Unit Repair and On-Vehicle sections in the appropriate model year service manual for repair procedures.

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.