10-1 Overdrive Oil Leak Potential

“A” Type Unit

Triumph TR2/3/3A/4/4A/250/TR6

BritCar ServiceWhen re-assembling the overdrive to the transmission adapter plate, it is important to observe the following in order to reduce the potential for transmission oil leaking at the adapter plate-to-overdrive coupling.

1. Before installing the adapter plate it is recommended that the threaded bolt holes for the adapter plate mounting be slightly countersunk. this relieves interference of the top thread against the gasket and plate allowing for a tighter joint when the bolts are torqued to the correct specification.

2. When installing the adapter plate on to the transmission and using lock wire to restrain the bolts, (this is the correct method for earlier “A” types), the wire connecting the lower two bolts MUST pass over the pump engagement boss/shoulder. If the wire passes under this projection, the adapter plate will not be allowed to seat against the gasket and if the coupling bolts are over-tightened in this condition, adapter plate damage will occur along with subsequent oil leakage.

3. Internal epicyclic train sun gear and Spragg clutch splines must be in line to permit uninhibited insertion of the transmission output shaft. Any mis-alignment will cause the output shaft to bind and any stressing of the transmission adapter plate can cause warpage at the center section, (at the two long drawing up bolt positions), resulting in a bent adapter plate and subsequent oil leak.

4. The overdrive oil pump cam can foul on the pump roller and result in the same adapter plate damage as above. The pump roller must be restrained in the lowest operating position either by using a wire tie, (to be removed when the cam is in position), or the cam must be physically placed onto the roller, as the overdrive and the transmission are brought together.

5. The large brass filter/drain plug should be examined to ensure no burrs exist on the sealing face. Quite often, it will be found that the plug has been removed by using a hammer and or punch thus causing the sealing surface to be damaged. Use the correct “C” style wrench to remove or tighten this plug. When filling the transmission with oil, recheck the oil level after 10 minutes as the oil transfer port to the overdrive restricts the oil flow into the overdrive pump sump. To avoid terminal damage to the overdrive internals, check oil level frequently. When the oil level is too low to operate the overdrive clutch, damage will have been done to the epicyclic gear train.