A/T - No Engine Braking In Drive 2 (D2) Selection
89chevy05GMC NUMBER: 88-T-200
GROUP: 7A - Automatic Transmission
DATE: February, 1989
CORPORATE
NUMBER: 877137
SUBJECT: NO ENGINE BRAKING IN DRIVE 2 (D2)
MODELS: 1978-88 TRUCKS WITH THM 400/475 TRANSMISSION
BULLETIN COVERS:
No engine braking in Drive 2 (D2) selector range caused by a broken plastic Front Accumulator Piston (303). The transmissions affected are the THM 400/475/HYDRA-MATIC 3L80/3L80-HD Transmission. The die cast aluminum piston can be used in service for this condition and will reduce the chance of any broken or cracked pistons.
Figure No. 1 - THM 400/475, HYDRA-MATIC 3L80/3L80-HD Transmission Identification Information:
DATE OF PRODUCTION CHANGE: (Figure 1)
August 1, 1988 (Julian Date 214) all 1989 THM 400/475/HYDDA-MATIC 3L80/3L80-HD Transmissions were built with the aluminum Front Accumulator Piston (303).
Figure No. 2 - Valve Body:
SERVICE PARTS INFORMATION: (Figure 2)
Service Part No. Part Description
8626883 Piston-Front Accumulator (303)
This part is currently available from GMSPO.
IMPORTANT: The plastic Front Accumulator Piston (8629080) should be replaced if found in any 1978-1988 Control Valve Assembly (049).
SERVICE MANUAL REFERENCE:
Refer to the Unit Repair Section of the appropriate Service Manual for proper replacement procedures. For replacement performed under warranty, use Labor Operation K 6560.