A/T - No Engine Braking In Drive 2 (D2)
88Chevy33Number: 88-378-7A
Section: 7A
Date: DEC., 1988
Subject: NO ENGINE BRAKING IN DRIVE 2 (D2)
Model and Year: 1978-88 TRUCKS WITH THM 400/475
FIGURE 1 - THM 400/475, HYDRA-MATIC 3L80/3L80-HD TRANSMISSION IDENTIFICATION INFORMATION:
FIGURE 2 - VALVE BODY:
TO: ALL CHEVROLET DEALERS
This 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.
DATE OF PRODUCTION CHANGE: (Figure 1)
August 1, 1988 (Julian Date 214) all 1989 THM 400/475/ HYDRA-MATIC 3L80/3L80-HD Transmissions were built with the aluminum Front Accumulator Piston (303).
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 1978-88 Control Valve Assembly (049).
SERVICE MANUAL REFERENCE:
Refer to the Unit Repair Section of the appropriate Service Manual for proper replacement procedure.