Hi Henry! I have built a number of overdrives and raced in SCCA with one
for 24 years. I agree with your guy. I always used the large accumulator
piston with 2 springs. In place of the normal inner spring I used a spring
from an Austin Healy unit (the Healy used the smaller accumulator
piston/spring combination, similar to the later Truimph A-Type overdrives).
Be sure to measure the compressed height of the Healy spring to make sure
it will not bind when installed. It's been a long time since I set one up
this way, but I believe we had to shorten the Healy spring slightly.
In fact, I rebuilt a stock Healy overdrive unit recently and had to order a
new accumulator spring for it. I got the spring from Overdrive Repair
Services, Sheffield, England. They are an excellent source for overdrive
parts. Contact Paul Winter (info@overdrive-repairs.co.uk). Tell him you
heard about them from me. He has been very helpful, and prices are
reasonable (the accumulator spring was 10 pounds sterling) I'm sure he
will also have the large accumulator spring, which you should replace also
to insure maximum pressure. This set up should give you about 500 - 525
lbs. of pressure which always worked fine in my race car. If you want
higher pressure, you can use shims, but I don't believe it is required.
Good luck.
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