TRANSMISSION OIL LEAKS HYDRA-MATIC TRANSMISSIONS

THE ATTACHED SERVICE BULLETIN IS A REVIEW OF PRIOR PUBLICATIONS AND CURRENT INFORMATION PERTAINING TO TRANSMISSION OIL LEAK CORRECTIONS. GENERAL DIAGNOSIS PROCEDURE GREAT CARE SHOULD BE TAKEN TO MAKE CERTAIN ANY OIL LEAK IS CORRECTLY DIAGNOSED AS TO TYPE AND LOCATION. IN SOME CASES IT HAS BEEN FOUND THAT AN INCORRECT LOCATION HAS BEEN REPAIRED DUE TO MISLEADING OBSERVATIONS. FOR EXAMPLE, A FRONT END LEAK CAN APPEAR AS A REAR END LEAK AS A RESULT OF WIND FLOW AROUND THE ENGINE AND TRANSMISSION. TRANSMISSION OIL LEAKS GENERALLY ARE IDENTIFIED BY THE RED DYE COLOR; HOWEVER, IN SOME CASES THE STAIN WILL BE VERY FAINT DUE TO THE TYPE OF DYE USED. FIRST, IT IS IMPORTANT THAT THE TRANSMISSION BE AS CLEAN AS POSSIBLE FOR THE PROPER IDENTIFICATION OF THE SUSPECTED OIL LEAK. RESIDUAL OIL FROM THE ASSEMBLY PLANT OIL FILL OPERATION COULD BE INTERPRETED AS A TRANSMISSION OIL LEAK. IN SOME CASES, AFTER THE TRANSMISSION HAS BEEN CLEANED, WHITE POWDER SHOULD BE USED FOR FURTHER IDENTIFICATION. PROPER LEAK IDENTIFICATION REQUIRES TWO TYPES OF TESTS AS FOLLOWS: COLD OIL CHECK - (ENGINE OFF) THIS TEST REQUIRES THAT THE TRANSMISSION BE COLD SO THAT THE OIL LEVEL IS ABOVE THE TOP OF THE BOTTOM PAN. THIS WILL INDICATE SOME LEAKS THAT CAN ONLY BE OBSERVED COLD AND WHICH ARE NOT DETECTABLE IN THE NORMAL HOT OIL LEAK INSPECTION. POINTS OBSERVED DURING THIS CHECK WOULD BE THE T.V. CABLE SEAL, THE FILL PIPE SEAL AND ALL OTHER POINTS ABOVE THE TRANSMISSION OIL PAN. HOT OIL CHECK - (ENGINE RUNNING) THIS IS THE NORMAL TYPE OF INSPECTION AND REQUIRES THAT BOTH THE TRANSMISSION AND THE ENGINE BE AT A TEMPERATURE, WHICH WOULD DUPLICATE HOT OIL OPERATING CONDITIONS. THE TRANSMISSION DIPSTICK SHOULD BE TOO HOT TO TOUCH OR ENGINE TEMPERATURE SHOULD BE ABOUT 200F (93C) POSSIBLE POINTS OF TRANSMISSION OIL LEAKS 1.TRANSMISSION OIL PAN A.PAN TO CASE BOLTS - UNDER TORQUED, IMPROPERLY INSTALLED, MISSING OR BROKEN. B.PUMP BUSHING - DAMAGED, MOVED. INSPECT PUMP GEARS, COVER AND BODY FOR DAMAGE. C.PUMP ATTACHING BOLTS - INCORRECTLY TORQUED, STRIPPED OR MISSING. INSPECT BOLT WASHER (IF USED) FOR DAMAGE. D.PUMP TO CASE SEALING RING - INSPECT RING FOR DAMAGE, CORRECT SIZE, LOCATION IN GROOVE AND CASE SURFACE. E.CONVERTER ASSEMBLY - INSPECT CONVERTER FOR LEAKS AT OUTER SEAM WELDS, HUB TO COVER WELD, HUB FINISH (ROUGH, ETC.) WHICH WOULD DAMAGE FRONT SEAL. REFER TO SERVICE MANUAL PROCEDURES. FRONT WHEEL DRIVE TRANSMISSIONS AND TRANSAXLES DUE TO THE PHYSICAL ARRANGEMENT AND DESIGN OF THE MODELS THM 325 AND THM 125, THEY PRESENT ADDITIONAL LOCATIONS TO BE OBSERVED IN THE PROPER DIAGNOSIS AND REPAIR OF TRANSMISSION OIL LEAKS. MODEL 125 1.OIL ON TOP OF TRANSMISSION CASE A.RESIDUAL OIL IN TOP CASE POCKET. B.TOP PRESSURE PLUG, INCORRECT TORQUE. IF A LEAK IS OBSERVED APPLY LOCTITE #59231 OR TEFLON TAPE (OR EQUIVALENT). 2.CASE COVER A.POROSITY B.CASE COVER GASKET OR BOLT TORQUE C.CASE COVER OR CASE FLATNESS. WHEN REPAIRING A LEAK ON THE CASE COVER USE LOCTITE 515. REF. HYDRA-MATIC SERVICE BULLETIN NO. 80-11. 3.AXLE SHAFT SEAL (SIDE) A.CUT, DAMAGED. EXCESSIVE SIDE LOAD OF SHAFT. 4.VENT A.TRANSMISSION OVER-FILLED. B.VENT PASSAGE IN CASE COVER (HYDRA-MATIC SERVICE BULLETIN NO. HM 81-14). MODEL 325 1.BOTTOM PAN AND OR CHAIN COVER A.INTERFERANCE BETWEEN CHAIN COVER AND PAN. ELIMINATE INTERFERANCE AND USE SMALLER WASHER HEAD BOLT (HYDRA-MATIC SERVICE BULLETIN NO. HM 79-10). 2.DIFFERENTIAL TO TRANSMISSION LEAK A.GASKET B.DIFFERENTIAL BOLTS NOT TORQUED. C.VENT HOLE IN DIFFERENTIAL ASSEMBLY.

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.