From: jonathon (jemery@execpc.com)
Date: Tue Dec 24 2002 - 06:57:24 PST
>About the only thing vacuum problems should cause
>is shifting at too high or too low a speed for the load conditions,
>but you will get the shift regardless.
Speaking of vacuum modulators, you don't need one at all. I got a tranny out
of a potato chip truck, a THM400 that was behind a Cummins 4BT that is, it
had a fixed screw type modulator. Another one I got had what looked like a
nornmal vacuum modulator with the input tube removed and a pan head wood
screw run down the middle of the can. In this particular application the
tranny shifted at X rpm (I think it was like 1750) no matter what. It was
kind of odd at times (I was able to drive the step van before the
engine/tranny was pulled out) but it was drivablen, not sure I'd want it
that way if I was towing something.
I decided to put something back in there (when I put the 4BT/THM400 into a
Dakota) so I could hold off my shifts if I was under load but the vacuum
system that is used on the GM diesel didn't impress me, and I didn' have
access to cheap parts, so I got a Morse cable modulator from an Allison 545
which goes right into the THM400 and works just fine. The other end connects
up to the throttle linkage at the pump. I do beleive that there is some
theoretical alteration that needs to be done to the plunger (to shorten it
for use with a 400) which I may do someday but for now it works well.
that is all,
je
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