1956 AMC Hudson Technical Service Manual Supplement

50
FOURTH SPEED 4-3 PART THROTTLE DOWNSHIFT
A 4-3 part throttle downshift can be made any time the transmission is in fourth gear and
the car speed is below approximately 30 M.P.H. This is desirable in traffic because the
transmission can be downshifted to third gear for faster pick up without a wide open throttle.
The part throttle downshift can be obtained in the following manner:
When the transmission is in fourth gear and the accelerator is depressed, approximately
IA down, throttle pressure on the plunger is directed through the 3-4 shift valve to the
regulator valve. Throttle pressure and spring force on the regulator valve will close the
valve and the transmission will be in third gear. When the shift valve closes, throttle
pressure from the plunger will be cut off and throttle pressure from the throttle valve will
hold the shift valve closed until the governor pressure can increase enough to open the
shift valve again for fourth gear. If pressure on the accelerator is released enough, the
governor pressure will open the shift valve immediately.