If a 1983 or 1984 THM 200C transmission exhibits oil exhausting out the vent pipe, possible causes may be due to out-of-flat conditions on the face, nicked faces, porosity, or face damage on the pump body assembly or the oil pump cover assembly.
When servicing any 1983 or 1984 THM 200C transmission for transmission oil exhausting out the vent pipe, both the pump body assembly and the pump cover assembly should be replaced. At the same time, a new pump to case gasket should also be installed. Replacement of these parts will prevent transmission oil from exhausting out the vent pipe during harsh deceleration or during sharp turns.
The following part numbers can be used to service all these THM 200C transmissions.
BH, PS, CZ, JY, OI, OR, OU 8638922
OR, OU 8633957
BH, PS, OI 8633958
BH, PS, CZ, JY, OI, OR, OU 8633899
Refer to your service manual for disassembly and reassembly 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.