A/T - Harsh Shift/3-4 Shift Cycling

90chevy04

GMC NUMBER: 90-7A-23


GROUP: 7A Automatic Transmission

DATE: December, 1989


CORPORATE
NUMBER: 967102
SUBJECT: HARSH SHIFT AND/OR 3-4 SHIFT CYCLING

MODELS: ALL 1980-1990 MEDIUM TRUCKS EQUIPPED WITH ALLISON AT-500 OR MT-600 SERIES, TRANSMISSIONS AND CARBURETED 350, 366 AND 427 GASOLINE ENGINES (RPO'S LF5, L86 AND L43) WITH VACUUM MODULATOR (VIN CODES A, B AND E)
Some of the subject vehicles may experience a harsh shift and/or 3-4 shift cycling due to low vacuum. To correct these conditions, a new "Service Only" vacuum modulator kit has been released.

PARTS INFORMATION:

Part Number Description

29051199 Vacuum Modulator Kit

Kit Includes:
29051199 Vacuum Modulator
8658110 O-Ring
Use the modulator kit only after appropriate troubleshooting has been completed. Verify the carburetor is performing properly and the vacuum lines are in good condition (no leaks or splits) prior to installing the new kit. The new vacuum modulator kit is purple in color and can be purchased through Allison Transmission Division Parts Distribution System. For vehicles repaired under warranty use:

Labor Operation: K6180
Labor Time: 0.2 Hrs.

Parts are currently available from your Allison Transmission Distributors and Dealers.