NO DRIVE/REVERSE THM 700-R4 MAY BE CRACKED OIL PUMP ROTOR. GMC Truck GMC Suburban

MODELS: 1982 AND 1983 LIGHT DUTY TRUCKS WITH THM 700-R4 TRANSMISSION

If a THM 700-R4 transmission experiences a loss of drive and reverse, a possible cause for this condition may be a broken or cracked oil pump rotor.

The oil pump rotor can be broken or cracked by:

1. Not engaging the converter hub slots completely into the lugs of the oil pump rotor during assembly.

2. Allowing the converter to hit on something, such as the floor or table, while handling the transmission assembly.

3. Dropping an oil pump rotor on the floor while handling.

SERVICE PROCEDURE

When servicing any THM 700-R4 transmission for a no drive or reverse condition, install an oil pressure gage to verify a broken oil pump rotor. If zero line pressure is obtained, the oil pump rotor could be cracked. If the oil pump rotor is broken or cracked, proceed as follows: (Refer to service manual if necessary.)

A. If the oil pump rotor is cracked, but not broken, replace the oil pump body. See chart for part number. If the oil pump cover assembly is scored or damaged, replace it also.

B. If the oil pump rotor is broken you must:

1. Replace the converter. Do not reuse the converter due to possible metal particle contamination.

2. Flush the transmission oil cooler and lines.

3. Disassemble and clean the valve body assembly.

4. Completely disassemble, clean, and inspect all internal components. Replace any damaged or worn parts.

5. Clean the transmission case thoroughly. Make sure all bores and channels are free of dirt and foreign material.

6. Inspect all bushings for scoring or damage. Replace if necessary.

7. Replace the oil pump cover and body. Refer to chart for part number.

8. Reassemble the transmission following service manual procedures.

YEAR PART MODELS PART NO.

ALL Oil Pump Body ALL 8642986 Assembly ALL Pkg., Overhaul ALL 8642953 Seals & Gaskets ALL Pkg., Overhaul ALL 8642954 - Complete 1982 Oil Pump Cover M6, MH, 8647190 Assembly TN, TP 1982 Oil Pump Cover All Other 8647189 Assembly Models 1983 Oil Pump Cover TS, TZ, 8647190 Assembly T8, TP, MH, VJ, TL, YH 1983 Oil Pump Cover T2, VA, 8647189 Assembly YN, ML, MP, MS, T7, YF, YG, PQ, YP, YK, Y9, TC, MB, MC, MJ, VN, TE, TH, TK, MD, ME, MK, MW, VH

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.