[Healeys] Overdrive Hydraulic Pump

[Mark Schneider]

I am finishing up a complete tear down and rebuild of a BJ8 gearbox  
and overdrive.  The car has 118,400 miles on it and the gearbox/OD has  
never been out of the car before.  Today we finished putting the  
overdrive together and planned to test it.  One of our club members  
had built a test apparatus which allows bolting the overdrive to a  
framework and spinning the main shaft with an electric motor.  We  
filled the OD with 30 weight non-detergent oil and ran the motor  
spinning the pump and watched the little pump oscillate up and down as  
it is supposed to. We let it run for about ten minutes.   However, we  
were never able to get any pressure built in the system, the pressure  
gauge never came off of zero.  In the tear down we did not remove or  
dismantle the pump.  In the 39 years I have owned the car the  
overdrive has never failed to engage or disengage smartly.  The reason  
I dismantled the overdrive was to replace bearings, thrust washers,  
and the accumulator piston, rings and housing.  The accumulator piston  
and housing had become badly scored.  While the OD  was apart I  
thoroughly cleaned the interior and flushed out all dirt and residue  
that had built up of the life of the car.   The only reason my  
colleagues and I could think of for the failure of the pump to begin  
to build pressure is if air had become trapped in the passages and the  
pump cannot clear the air out.  I s there anyway to prime the pump?   
Or does anyone have suggestions for the cause of an untouched working  
pump suddenly failing to work when the unit is re-filled with fresh oil?

Marks 3