A/T - Front Pump Bushing Walk-out
88Chevy33Number: 88-371-7A
Section: 7A
Date: NOV., 1988
Subject: FLUID LEAK CAUSED BY FRONT PUMP BUSHING WALKOUT
Model and Year: 1978-88 LIGHT DUTY TRUCKS, G AND P VANS WITH THM 400/475 TRANSMISSION
FIGURE 1:
FIGURE 2:
TO: ALL CHEVROLET DEALERS
Some THM 400/475 models may experience a fluid leak coming from the converter or oil pump area. This could be caused by the front pump bushing walking forward, resulting in fluid being forced past the pump oil seal. A new bushing was introduced that has an increased hardness specification which results in a higher push-out load.
DATE OF PRODUCTION CHANGE: (Figure 1)
Beginning August 1, 1988 (Julian Date 213) all 1989 THM 400/475 transmissions were built with the new pump bushing.
IMPORTANT: When replacing the pump bushing (003) it is required that the pump seal (002) also be changed at this time. (Figure 2)
SERVICE PARTS INFORMATION:
Part No. Part Description
8623940 THM 400/475 Bushing-Pump Body
Parts are currently available from GMSPO.
8670283 Helixseal Assembly-Oil (optional with 8670284)
SERVICE MANUAL REFERENCE:
Refer to the Unit Repair section of the appropriate Service Manual for the proper pump bushing and seal replacement procedures.