Join Date: Mar 2002
Location: Austin, TX, USA
<BLOCKQUOTE>quote:</font><HR>Originally posted by CFunK:
As long as this thread is going I have a couple of similar questions.
Is the governer responsible for part throttle upshifts? With light throttle mine shifts real soon. Already went the adjustable modulator route without much change. I wasn't expecting much but it was an easy swap.
What is responsible for part throttle downshifts. Third to 2nd NOT at WOT.
The govenor is a pressure regulator that varies "govenor pressure" with vehicle speed. The modulator is a pressure regulator that varies "modulator pressure" with engine load (sensed by vacuum). Each shift valve has govenor pressure pushing against one end with modulator pressure and a spring pushing against the other. Various springs in the govenor, modulator, and shift valves set up a balance. When govenor pressure is high enough to overcome the pressure of the shift valve spring and modulator pressure the valve begins to move and eventually toggles moving fully to the shifted position.
Part throttle downshifts occurr when modulator pressure rises sufficiently that it overcomes govenor pressure. Shifting too soon can be caused by improperly installing shift valve springs (too light of spring), missing springs on the govenor causing govenor pressure to be too high, or a messed up modulator circuit causing modulator pressure to be too low.
I can explain a bit more, but I urge you to find out what is causing the transmission not to shift correctly before modifying anytning. It wouldn't hurt to verify that the modulator valve is correctly installed (inside the case). Don't use a magnet to remove the modulator valve since it can magnatize it and cause steel particles to jamb it up. It can be finessed out with a pick probe. Make sure the modulator vacuum line is connected to manifold vacuum.
Is it possible that the transmission came from a car with a lower rear-end ratio and you're running it with a high ratio rear end (i.e. 4.11:1)? If so you may need to reshape the weights, or stiffen the springs in the govenor assembly. There are some other possible govenor problems that cause cause the transmission to shift too soon. Looking at the first port above the weight assembly (govenor in your hand with the weights down and gear up) You'll see the govenor valve partially exposed in the opening. See that a 0.020 feeler guage just slips in between the top of the port and the valve land. If not, you'll have to take the govenor apart and bend the tangs on the inner weights evenly. Ask me and I'll email you some pictures and text explaining any weight reshaping you might have to do.
Generally it is desirable for a transmission to shift soon. If you are racing, manually shift it. Doing so will engage an extra band in 2nd gear and increase apply pressure in first. Generally though shifts should occurr later and firmer the more you accellerate due to the modulator. The detent cable should cause a WOT downshift.