1956 AMC Hudson Technical Service Manual Supplement

38 TRANSMISSION AND OVERDRIVE
below 65 M.P.H. the 4-3 shift valve will close for a 4-3
downshift, and at speeds below 20 M.P.H., the 2-3 shift
valve will close for a 3-2 downshift.
PUMP PRESSURE
The first requirement of a hydraulic control system is a
source of oil pressure. Oil pressure for the Hydra-Matic
transmission is supplied by two oil pumps. One is at the front
of the transmission, driven by the engine, the other at the
rear, driven by the transmission output shaft. The front pump
operates whenever the car is in forward motion.
The front pump is of the vane type and consists of seven
vanes rotated within a movable slide by a rotor. Variable
output is achieved through the movable slide. A priming
spring holds the slide up to deliver maximum output to
quickly attain regulated pressure in the control system when
the engine is started. The pressure regulator will then adjust
the position of the slide so that only the amount of oil
required is pumped. Main line pressure operates on the end
of the pressure regulator and tends to move it downward.
When the pressure regulator is in the upward position, oil is
directed to hold the slide up for maximum output. Oil is
directed to the opposite side of the slide when the pressure
regulator is forced down and the volume output of the pump
will be decreased to the amount required to maintain regulated
pressure.
The torus feed valve controls the flow of oil to the fluid
coupling, the valve is held against the slide by the spring.
The valve closes the oil passage to the fluid coupling until
oil pressure moves the slide toward the priming springs. The
valve follows the slide and opens to direct oil through the oil
cooler in the radiator lower tank, through the fluid coupling
and lubrication system. A ball check is provided to by-pass
the cooler in the event the cooler becomes plugged. The limit
valve in the front clutch valve body protects the system
against excessive pressures. The rear pump is a gear type.
Both pumps deliver oil at regulated pressure (controlled by
the pressure regulator valve through the front pump) when
the car is driven forward.
THROTTLE PRESSURE
Throttle valve pressure originates at the throttle valve and
varies according to carburetor throttle opening by means of
linkage from the accelerator pedal. As the accelerator pedal
is depressed, linkage to a lever on the side of the transmission
moves the throttle valve plunger. Plunger movement
opens the throttle valve through spring force, and oil from
the pump then flows through an opening at the throttle valve.
This oil under pressure acts on the end of the throttle valve
to oppose the throttle valve spring force which opened the
valve. In this manner, the throttle valve comes a balanced
valve; balanced between spring force and throttle pressure.
As a result of this action, throttle pressure varies with accelerator
pedal position from zero pressure at closed throttle to
full line pressure at full throttle. Throttle pressure is directed
to a land on the throttle valve plunger to assist in moving the
plunger which gives a lighter feel to the accelerator pedal.
This pressure cannot move the plunger without assistance
from the accelerator linkage.
Throttle valve pressure is directed to the 2-3 and 3-4
regulator valves where it is modulated. Throttle valve pressure
acts against the end of these valves, and due to their
design, the pressure of the oil passing the valves is reduced.
It is, therefore, called modulated throttle valve pressure.
This pressure assists the 2-3 and 3-4 shift valve springs in
opposing governor pressures.
Throttle valve pressure is directed to one end of the
overrun clutch valve to position it to the right and to the
coupling valve plug to assist the coupling valve spring in
opposing G-1 booster pressure.
Throttle valve pressure is directed to the transition valve
when in detent position for a 3-2 downshift to prevent a
3-1-2 downshift by properly timing the front and rear unit
change.
Throttle pressure is directed to the accumulator to absorb
the shock of the rear clutch apply oil pressure.
GOVERNOR PRESSURE
A centrifugal governor driven by the rear pump supplies two
governor pressures. G-1 is supplied from the governor valve
having the large weight. G-2 is