DIAGNOSING TRANSMISSION OIL LEAKS - THM 700R4

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

To diagnose a transmission oil leak properly the following procedure should be used.

DIAGNOSIS PROCEDURE

1. Clean all residual oil from the transmission. (C.R.C.'s electromotive cleanser or equivalent is recommended). Repeat cleaning process until all residual oil is removed.

2. Dust the entire transmission with a white powder (eg. leak tracing powder or spray foot powder). If residual oil is left on the transmission, it will necessitate the cleaning and dusting procedure be repeated.

3. After normal operating temperature (170 DEG F) has been obtained, let the transmission stand for at least thirty (30) minutes (engine off).

4. Inspect the transmission for leakage by following red oil traces left in the powder.

5. Once the leak has been diagnosed as to location and type (wetness, moist, damp, etc.), refer to the following repair procedure:

IMPORTANT: Steps 1-4 should be used when diagnosing any transmission for an oil leak.

6. Repeat steps 1-4 following repair of suspect leak source.

REPAIR PROCEDURE:

POSSIBLE LEAK POINT

FIG.ITEM NO. NO. PART NAME LEAK CAUSE CORRECTION

1 1 Transmission Oil Pan Low Bolt Torque Retorque & Recheck Bolts Gasket Leak Remove & Replace Gasket

1 2 Case Porosity Repair Per Service Manual Cracked Replace Case

1 3 Cooler Fittings Or Low Torque Reseal & Retorque Pressure Plugs Recheck

1 4 T.V. Cable Connector Connector Cocked & Remove Connector & Interfering Reinstall With Mount Seal Damaged Remove & Replace Seal Connector Cracked Remove & Replace Cable

1 5 Servo Cover Porosity Replace (See Figure 2) 2 1 "O" Ring Damaged Replace (See Figure 2) 2 2

1 6 Fill Tube Seal Missing Or Remove Fill Tube & Damaged Replace Seal Tube Bent Above Replace Tube Transmission

1 7 Converter Seal Seal Damaged Replace Seal 3 - Seal Blown Out (See Figure 3) Check For Seal Leak Oversized Seal Bore Or (Not Damaged) Restricted Drainback Passage

1 8 Pump Assembly Pump Bolts Loose Retorque & Recheck Pump To Case Ring Remove & Replace Ring Cut or Damaged (Recheck. If Leak Persists, Replace Oil Pump Body With Part Number 8642986 or Repair (See Figure 3) 3 - Pump Porosity Replace Pump Body Part Number 8642986

1 9 Converter Assembly Hub Or Seam Weld Replace Converter Leak 1 10 Vent Leaking Check For Oil Overfill & Correct As Necessary

1 11 Electrical Connector "O" Ring Missing Remove Connector & Or Damaged Replace Seal Connector Missing Remove & Replace Or Damaged Connector

1 12 Manual Shaft Seal Assembly Remove & Replace Seal Damaged 1 13 Governor Cover Gaps In Sealant Reseal (Loctite or R.T.V.) Remove & Replace

1 14 Speedo Fitting Low Bolt Torque Retorque Bolt & Recheck Seal Damage Remove & Replace

1 15 Rear Extension Porosity Repair Per Service Manual Cracked Replace Low Bolt Torque Retorque & Recheck Extension To Case Replace Seal Damaged Extension Seal Replace Assembly Torn Or Damaged

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.