INFORMATION ON NEW TWO PLATE 4TH CLUTCH ASSEMBLY

Model and Year: 1990 A, W CARS WITH 4T60/440T4 AUTOMATIC TRANSMISSION

I. NEW TWO-PLATE 4TH CLUTCH ASSEMBLY

BULLETIN SECTION COVERS: (Figure 1)

A new two-plate 4th clutch assembly (501) and apply plate (502) are used to replace the single plate 4th clutch assembly for some 1990 HYDRA-MATIC 4T60 (THM 440-T4) transaxles. The extra plate was added for higher torque engine applications. For this change to be implemented, the following parts were modified:

- 4th clutch plates assembly (fiber) are thinner by 0.51 mm (0.020"). The fiber material is the same thickness; only the steel part of the plate was made thinner. The two-plate assembly has four white stripes, while the single plate fiber plate has four green stripes.

- 4th clutch reaction plates are made thinner by 0.1 mm (0.004") for the two-plate assembly.

- 4th clutch apply plate does not have the step used on the single apply plate, but it does have a slight machined-in taper.

DATE OF PRODUCTION CHANGE:

Starting SOP 1990, all transaxle models covered by this bulletin were built with the two-plate 4th clutch assembly.

SERVICE PROCEDURE: (Figure 2)

When servicing a 1990 transaxle model, rebuild/replace the 4th clutch components with the same type (single or two-plate) unless the 4th clutch is distressed; see Section 11 of this service bulletin for service procedure. The part numbers for the two-plate 4th clutch assembly components and overhaul repair packages are listed under "Service Parts Information."

IMPORTANT: Do NOT interchange individual components or the entire 4th clutch assembly into a unit that was not originally built with it. Calibrations of the 4th clutch apply feel will be affected and could create durability concerns.

SERVICE PARTS INFORMATION:

Model Part Number Description Year Model Usage

18017246 Plate Assembly - 4th Clutch 1990 OAAH OABH OAFH (fiber for two-plate type) OAJH OANH OATH *OBAH *OBDH *OBFH *OBHH *OBJH *OBPH *OBWH

8661004 Plate Asm. - 4th Clutch Apply 1990 OAAH OABH OAFH (for two-plate type) OAJH OANH OATH *OBAH *OBDH *OBFH *OBHH *OBJH *OBPH *OBWH

8661006 Plate Asm. - 4th Cl. Reaction 1990 OAAH OABH OAFH (steel for two-plate type) OAJH OANH OATH *OBAH *OBDH *OBFH *OBHH *OBJH *OBPH *OBWH

8662986 Pkg. - Overhaul Repair Complete 1990 OAAH OABH OAFH (1990 two-plate clutch models) OAJH OANH OATH *OBAH *OBDH *OBFH *OBHH *OBJH *OBPH *OBWH

8662989 Pkg. - Overhaul Repair Complete 1990 *OBAH *OBDH *OBFH (1990 single plate cl. models) *OBHH *OBJH *OBPH *OBWH OCHH OCJH OLMH OLNH

Parts are currently available from GMSPO.

* Models were produced for a short time from SOP 1990 to July 31, 1989 (Julian Date 212) with the two-plate 4th clutch. Starting July 31, 1989 (Julian Date 212) these models were built with the single plate 4th clutch.

SERVICE MANUAL REFERENCE:

Refer to the appropriate 1990 Service Information Manual for service procedures.

II. DISTRESSED TWO-PLATE 4TH CLUTCH ASSEMBLY SERVICE INFORMATION FOR 3300 AND 3800 ENGINE TRANSAXLE MODELS

BULLETIN SECTION COVERS: (Figure 2)

Service information for a distressed two-plate 4th clutch assembly. Some 1990 transaxle models for the 1990 A cars equipped with a HYDRA-MATIC 4T60 (THM 440-T4) and a 3300 or 3800 engine may have a new style 4th clutch plate assembly. If service is required for a distressed 4th clutch assembly, follow the procedure listed under "Service Procedure."

The following models were scheduled to be produced with a two-plate 4th clutch assembly for the start of production of the 1990 model year: OBAH, OBDH, OBFH, OBHH, OBJH, OBPH, OBWH and OPAH.These models will now have the previous single plate 4th clutch assembly.

IMPORTANT: Do not update a single plate 4th clutch assembly transaxle model to the two plate style; the 4th clutch apply feel will be affected.

The 1990 Service Manual should be updated to show that some models are produced with the two-plate 4th clutch assembly.

DATE OF PRODUCTION CHANGE:

Models OBAH, OBDH, OBFH, OBHH, OBJH, OBPH and OBWH built after July 31, 1989 (Julian Date 212) will have the single plate 4th clutch assembly instead of the two-plate 4th clutch assembly.

SERVICE PROCEDURE:

If service is required for a distressed two-plate 4th clutch assembly, install the service package listed under "Service Parts Information" that will contain the previous single plate 4th clutch assembly, 4th clutch apply plate and calibration conversion components.

IMPORTANT: The valve body assemblies for the two-plate 4th clutch will not be available for the following models: OBAH, OBDH, OBFH, OBHH, OBJH, OBPH and OBWH. If a valve body assembly is required, order the valve body assembly from the GMSPO catalog (single plate calibration) and also order the single plate 4th clutch package listed under "SERVICE PARTS INFORMATION." Install all parts from the package.

POSSIBLE MISBUILDS IF PARTS ARE MIXED:

1. If a technician converted a single plate to a two-plate 4th clutch assembly without changing the valve body assembly, this would create a harsh 4th clutch apply.

2. If a technician converted a two-plate to a single plate 4th clutch assembly without installing the calibration conversion components (1 -2 accumulator bushing/valve) from the single plate 4th clutch package, this would create a very soft 4th clutch apply feel.

SERVICE PARTS INFORMATION:

Model Part Number Description Year Model Usage

8668980 Package - Single Plate 4th Clutch 1990 OBAH OBDH OBFH - Plate Assembly, 4th Clutch - Plate, 4th Clutch Apply - Plate, 4th Cl. Reaction (two in pkg.) - BushingNalve 1-2 Accumulator - Instruction Sheet

8668981 Package - Single Plate 4th Clutch 1990 OBHH OBPH OBWH - Plate Assembly, 4th Clutch OBJH - Plate, 4th Clutch Apply - Plate, 4th Cl. Reaction (two in pkg.) - BushingNalve 1-2 Accumulator - Instruction Sheet

Parts are expected to be available for part numbers 8668980 and 8668981 on 01-02-90. 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.

SERVICE NOTES:

The transaxle model OPAH was not built with a two-plate 4th clutch assembly, so there is no single plate 4th clutch conversion service package.

SERVICE MANUAL REFERENCE:

Refer to the appropriate 1990 Service Information Manual for service 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.