PUMP FLUID LEAK FRONT PUMP BUSHING WALKOUT

Model and Year: 1978-88 LIGHT DUTY TRUCKS, G AND P VANS WITH THM 400/475 TRANSMISSION

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.

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.