OIL PUMP SEAL ASSY LEAKS SERVICING THM 700-R4
MODELS: LIGHT DUTY TRUCKS WITH THM 700-R4 TRANSMISSIONS
Beginning March 7,1983, all THM 700-R4 transmissions were built with a revised oil pump body (part number 8642986). As shown in Figure No. 1, the oil drainback passage in the revised pump body connects with one of the core slots. This design change allows for more effective oil drainback, thereby relieving pressure under the oil seal assembly.
SERVICE INFORMATION
When servicing a THM 700-R4 built prior to this change which either - (1) pushes the oil seal assembly out of the oil pump body or (2) forces oil past the lip of the seal around the converter hub. Correct the drainback restriction as follows:
1. Following the service manual procedure, remove and disassemble the oil pump assembly.
2. Place the oil pump body on a cloth to protect the oil passage face. With a 6.0 mm (1/4") drill bit, enlarge the hole at point "A" to a depth of 12.9 mm (1/2 in.) maximum. See Figure No. 2. Hole "A" must connect with the drain back passage (Figure No. 2).
3. Turn the pump body over and inspect the drainback passage at point "B" (Figure No. 2). If the drainback passage is restricted at point "B" (ie. the two passages do not meet evenly), use a 8.0 mm (3/8") drill bit and enlarge the passage at point "C". Do not drill any deeper than necessary to remove the restriction.
4. Clean out any metal chips and reassemble the oil pump using the service manual procedure.
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.
