I have an A-Type overdrive in a TR4 that is slipping under load. Classic
problem, I know, but bear with me please. It started out as a standard
rebuild on a unit that had only 300-350 psi and wouldn't hold. It is a
single-spring accumulator type. The piston rings were broken and it was
dirty and basically clapped out so I did a standard rebuild of both the OD
and gearbox, replacing all wearing components in the overdrive including the
large thrust ring bearing.
When done, I got 420 psi on the bench and it would not hold at all in OD
when installed and put on the road, slipping out at the slightest throttle
increase. I had the pressure gage in place for the road test and the
pressure was steady except for the usual temporary drop when engaged. I
ruled out any electrical issues by powering the solenoid directly by hand
with a jumper.
I took it out of the car again for inspection and found nothing unusual.
There is plenty of liner surface left so I cleaned the cone clutch
thoroughly and roughed up the surface to remove any glazing. Since the
slipping point is between the clutch outside liner and break ring, I set the
brake ring on the bench and lowered the cone clutch slowly to mate them up
and thought there was a less than even contact. In other words, the clutch
looked like it could be slightly oval and therefore would have a two-point
contact rather than circumferential contact all around. It seemed to wobble
slightly instead of being a tight even fit. It was ever so slight and after
several attempts, I wasn't even sure it was a problem. It's hard to measure
the clutch and break ring diameters because of the tapered surfaces. I wish
I had put in a lathe to check the runout.
To make a long story even longer, I added a washer or two under the
accumulator spring and put it back in the car. Now I have no less than 525
psi which should be more than enough. The overdrive now kicks in and holds
at steady highway speeds but kicks down like an automatic transmission when
slightly more throttle is applied. It's worse in second and third gears
because of the higher torque. It has to come out again and my plan is to
change out the clutch and brake ring since I don't know what else to focus
on. Any other ideas or suggestions?
Thanks,
Mike
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