It sounds like your operating valve is sticking; I presume that this is
the "pressure valve on the right side" that you talk about. This might
be caused by the return spring being weak, or a burr hanging up the
spring or valve itself. When you pull the sealing cap, does it try to
pop off under spring pressure?
Another possible cause is that the hole at the bottom of the operating
valve hole is getting choked.
If you stop the car (which stops the pump and should allow the pressure
to go down) does the overdrive disengage?
Have you checked the filter on the side of the unit to see if there is
detritus in the oil supply? Tried changing the oil? If you want to
experiment a bit, you might drain the oil, fill with ATF and drive for
30 miles or so, then drain and refill with normal tranny oil - the ATF
should clean things out a bit. Clean the filter screen each time.
There's no one in the US that specializes in D type overdrives. I do
them from time to time, and have thought of starting a service for this
sort of work, but really haven't had the extra time... given how many
Spitfires are out there, I suspect that there really are a lot of D
types that could use help.
There are a few places in the UK that can help you out; John Kipping is
the most likely suspect.
Name: John Kipping Spares
Address: Parrots Grove
421 Aldermans Green Road
Coventry CV2 1NP
ENGLAND
Phone: (+44 203) 645 333
(+44 203) 645 030 fax
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