PUMP WHINE OR MOAN NOISE NEW PUMP DESIGN/THM 700-R4

MODELS: 1985-87 LIGHT DUTY MODELS WITH THM 700-R4 AUTOMATIC TRANSMISSIONS (MDB)

Whine or moan on a 1985 through 1987 (before 1986, Julian date 301) THM 700-R4 transmission may be caused by line pressure instability in a seven-vane pump design. A ten-vane pump design to provide stable fine pressure is now used on all 1987 THM 700-R4 models and available to service a 1985 through 1987 model transmission.

DATE OF CHANGE (Figure No. 1)

October 28, 1986, Julian date 301, ten-vane pumps for all 1987 THM 7W-R4 production and service replacement transmission assembly (SRTA) models.

SERVICE ACTION

When using the ten-vane pump body assembly to service a THM 700-R4 transmission, mate the new pump body to the pump cover taken from the transmission's existing oil pump.

SERVICE PARTS INFORMATION

8649964 - ten-vane pump body assembly (Figure No. 2) 1985-1987 models.

Due to a pump cover casting change in 1985, a 1982 through 1984 THM 700-R4 transmission must be serviced using a complete pump assembly. Service parts for these earlier model years will be available at a later date.

SERVICE MANUAL REFERENCE

Refer to the oil pump assembly section of the 1987 THM 700-R4 unit repair service manual.

SERVICE NOTES

Seven-vane pump body assemblies, part number 8649950, should normally be used to service 1985 through 1986 THM 700-R4 transmissions until current service stock is depleted. The ten-vane pump body assemblies should be used for any 1985 through 1986 model exhibiting a whine or moan condition and all 1987 THM 700-R4 transmission models.

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.