Mike
I don't believe that if an O/D drops out is a function of speed but more
one of distance. The O/D pump works on the output shaft that drives the
wheels, as you say. If you have been travelling any significant
distance, say perhaps 100 feet then the accumulator will be fully
charged with something like 400 psi oil pressure available.
The manual advises working the O/D valve six or seven times before
working on the O/D. This is to relieve the pressure from the accumulator
that might still be there after many hours and is therefore dangerous.
I suggest that if your O/D drops out around 30 mph the oil pressure has
dropped, again as you suggest. On a correctly working unit this should
not be the case. Either the control valve is being operated somehow or
there is an internal leak inside the unit. The most likely cause is a
badly seating valve but it could be leaks around the operating or
accumulator pistons.
Regards
>I am by no means an expert on overdrives. However, I thought the hydraulic
>pressure required to engage the overdrive was created by a pump driven by the
>main propshaft, and that at road speeds below about 30 mph there is
>insufficient pressure to engage the overdrive. That is certainly the case with
>the overdrive in my Triumph based home build Lotus Seven replica. So even if
>for some reason the gearbox switch is still providing 12 volts to the
>solenoid, at low road speeds there would be no possibility of being in
>overdrive and reverse. My 100 has the throttle switched bypassed, but the
>gearbox switch is in circuit. If I leave the dashboard switch on, and reduce
>speed, it always drops out of overdrive sometime before I come to a halt.
--
John Harper
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