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1982 - 1991 Corvette: Service Bulletin: New Output Shafts and Seals (Product Service Information)

Model and Year:
1982-91 C1/C2, G1/G2, K1/K2, S/T
1987-91 R/V
1985-91 M AND
Source: Chevrolet Service Bulletin
Bulletin Number: 91-390-7A - (08/01/1991)

Bulletin Covers:

HYDRA-MATIC 4L60 output shafts and input housing to output shaft seals have been revised to provide increased lube flow. Since lube hole locations have changed, the input housing to output shaft seal has been revised to accommodate them.

Date of Production Change:

Beginning January 28, 1991 (Julian Date 028), all HYDRA-MATIC 4L60 transmissions were built using the new output shafts and seals.

Service Information:

The NEW SEAL can only be used on the NEW OUTPUT SHAFTS. If the new seal is used on a previous model output shaft, the seal will block one of the lube passages.

The previous seal can be used on both the new and previous output shafts.

The new output shafts and seal will service any HYDRA-MATIC 4L60/THM 700-R4 transmission ever built.

The new output shafts can be identified by lube hole location. They have a lube hole on the chamfer at the front of the output shaft. The lube hole was previously located on the shank of the output shaft.

Service Parts Information:

The new output shafts and seals will become available for service as current stock is depleted at GMSPO.

Reference the GMSPO parts catalog for the correct output shaft to order for your specific transmission application.

Service Manual Reference:

Refer to the Automatic Transmission Unit Repair Section of the appropriate service manual for output shaft and seal removal and installation information.

Note:  See Attachment for full image.

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.

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