1990 Corvette: Service Bulletin: New Low and Reverse Clutch Support Selective Plate Dimensions

Subject: NEW LO & REV. CLUTCH SUPPORT SELECTIVE PLATE DIMENSIONS
Model and Year: 1990 B, F, Y CARS AND ALL TRUCKS AND VANS WITH 4L60 (700-R4) AUTOMATIC TRANSMISSION
Source: Chevrolet Service Bulletin
Bulletin Number: 90-223-7A - (05/21/1990)

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 90-166-7C. THE PART NUMBER HAS BEEN CORRECTED FOR THE NEW LO AND REVERSE CLUTCH AND SUPPORT ASSEMBLY. ALL COPIES OF 90-166-7C SHOULD BE DISCARDED.

This bulletin covers a dimensional change in the low and reverse clutch support and its selective plates. The thickness of the low and reverse clutch support has increased while the thickness of the selective plates has decreased. Three selective plates are available.

Production changes occurred in two phases which are shown below. (See Figure 1.)

Date Part Change Implemented

November 1, 1989 Low and Reverse Clutch Support (Julian Date 305)

February 2, 1990 Selective Plates (Julian Date 033)

In most cases, the new low and reverse clutch assembly will only require a fifth reaction plate instead of a selective plate.

The only way to identify the new low and reverse clutch support is to measure its thickness with a micrometer. (See Figure 2.)

The new low and reverse clutch support and selective plates may be used to service some past model year transmissions if:

- Transmission was built after February 9, 1987 (Julian Date 040).

NOTICE: The SELECTIVE PLATES are not interchangeable between the previous clutch support and the new clutch support. If selective plates are installed in the wrong clutch assembly, durability of the low and reverse clutch will be reduced.

NEW LOW AND REVERSE CLUTCH ASSEMBLY:

Part Name Part Number Dimension (mm) Identification

Selective Plate 8673548 1.168-1.314 8 Selective Plate 8673549 2.198-2.344 9 Reaction Plate 6261120 None

Clutch Support 7.671-7.849 None

Low and Reverse Clutch 8673544 and Support Assembly

PREVIOUS LOW AND REVERSE CLUTCH ASSEMBLY:

Part Name Part Number Dimension (mm) Identification

Selective Plate 8667584 2.386-2.557 4 Selective Plate 8667585 3.101-3.272 5

Clutch Support 6.655-6.909 None

Low and Reverse Clutch 8663094 and Support Assembly

Parts are currently available from GMSPO.

Refer to the HYDRA-MATIC 4L60/THM 700-R4 Automatic Transmission Unit Repair section of the appropriate Service Manual for removal and installation 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.