HARSH 1-2 UPSHIFT INSTALL SERVICE PACKAGE

SUBJECT: HARSH 1-2 UPSHIFT (INSTALL SERVICE PACKAGE)

MODELS: 1992 C/K, S/T TRUCKS AND M/L/G VANS WITH 4L60 TRANSMISSION

CONDITION (Figure 1):

Some vehicles equipped with a 1992 HYDRA-MATIC 4L60 transmission built between Julian Date 061 (March 1, 1992) and Julian Date 171 (June 19, 1992) may experience a harsh 1-2 upshift.

NOTE: Once the transmission is brought to operating temperature, the condition may not be able to be reproduced until a 'cold soak' (overnight) is performed.

CAUSE:

------ The above condition may be caused due to a tapered 1-2 accumulator sleeve. The tapered bore may cause the 1-2 accumulator valve to stick in the bottom of the bore.

CORRECTION (Figure 2):

To improve the 1-2 shift, install the service package listed in this bulletin. A 1-2 accumulator valve and 1-2 accumulator valve sleeve (which, normally, is not serviceable) is included in the package.

SERVICE PARTS INFORMATION:

Package Transmission Models Number -------- -------------------------------------- 8687992 2AAM, 2ACM, 2BAM, 2BBM, 2BCM, 2BHM, 2BRM, 2BWM, 2CAM, 2CBM, 2CCM, 2CFM, 2CHM, 2CJM, 2FTM, 2FUM, 2HBM, 2HLM, 2KHM, 2KJM, 2KMM, 2LHM, 2MJM, 2SHM, 2TLM, 2TWM, 2WAM, 2WBM, 2WCM

8688900 2ADM, 2AKM, 2CPM, 2FZM, 2HDM, 2MDM, 2MSM, 2TAM, 2TBM, 2YAM, 2YCM

Parts expected to be available on September 14, 1992. In case of limited inventory, parts will be placed on 400 control to waive VIP surcharges. Only verifiable emergency VIP orders will be accepted. GMSPO will make every effort to obtain parts. However, the part will be shipped premium transportation at dealer's expense and all other order types will be placed on back order until the 400 control is removed. Until then, the only avail- able service option will be the complete replacement control valve assembly which can be ordered from GMSPO.

WARRANTY INFORMATION:

Use Operation Number: T7601 Time: 1.8 Hrs. C/K, S/T Trucks M/L/G Vans

SERVICE MANUAL REFERENCE:

Refer to the HYDRA-MATIC 4L60 Unit Repair Section of the appropriate service manual for repair 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.