Hey James,
You did quite a bit of rebuilding on this overdrive so I bet you know more
about it than me at this point. I just rebuilt my own overdrive so a lot of it
is still fresh in my mind so I think I am following most of your description.
So here is my 2 cents.
If you are using the original pistons, these have rings with gaps in them so
you will get a little leak by and that could be the source of the hissing. Gas
is a lot less viscous than gear oil! The replacement pistons have an oring so
you wont get leak by with those (as much anyway). I'm not sure if you
mentioned putting any oil on parts during the assembly but you might be
getting a little sticktion with the whole mechanism and 100psi air might not
be enough to get it to clunk.
As I read over your Email I see that you replaced orings on the pistons so I
guess that you have the o-ring type pistons and again you probably won't get
much leak by there but I bet those require a little more pressure to slide
without any oil present.
One more idea I have, has to do with the ball check valves. if these are dry
(no oil) then they might need a little help from gravity to seat properly,
especially when using only air, so try rotating the mechanism to help them
out. If I remember this properly its the valve on the accumulator that needs
to close to get things going and that is on the left side so you would want to
turn the left side up (I think, big guess on my part here). The other check
valve is being opened by moving the lever and this is up and down in the
normal configuration but proper operation does require it to be closed for the
accumulator to accumulate pressure, which takes a bit of time with oil but not
with air pressure.
Anyway, I hope I've given you some ideas.
Sincerely
Rick Neves
Millis, MA 02054
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