If it will not shift no matter how fast you go, the modulator is not your problem. The design of the valve body and line pressures are setup so the modulator valve raises or lowers line pressure depending on vacuum(engine load) .
About the kickdown cable adjustment? that simply boosts the line pressure which causes a delayed shift or forced downshift. It will also be overridden if line pressure is high enough(pressure will be overidden at 40-45mph in 1st). So eventually if run past this point it will go ahead and shift. If its not shifting after that point its likely you have trash in the valve body or stuck valve.
Typically most problems will lead you to a stuck valve or cut seal when installing. Very easy to "shave" a seal when installing.
One good thing though... If its staying engaged in 1st and does not "freewheel" at the normal 2nd range 18-35mph, then atleast you dont have a piston seal or clutch pack problem.
Check the govenor (its quick and easy to pull), Pull the gear, levers and make sure there is no trash in the ball seats. If that doesnt help, sounds like you need to R&R the valve body and go through it again. You did disassemble it during the rebuild and clean all passages right?
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'71 LWB
350/350T, PS/PB
Special options? Yes, RUST... Need some?
Garrett
Olathe, Kansas
[This message has been edited by Zkast (edited May 17, 2002).]