1956 AMC Hudson Technical Service Manual Supplement

HYDRA-MATIC TRANSMISSION 27
Rear Unit—Clutch
To obtain direct drive in the rear unit, a multiple disc clutch
will lock the internal gear mechanically. The application of
the rear clutch is controlled hydraulically.
REVERSE UNIT
The reverse unit consists of a reverse planetary gear set
with a cone clutch which holds the reverse internal gear.
The reverse cone clutch is engaged by a piston which is oil
applied and spring released.
Located in the reverse carrier assembly is a parking pawl
sprocket. This sprocket has external teeth which receive a
parking pawl and provide a positive lock when the selector
lever is in the "P" (Park) position. In the park position, it
will be possible to start the engine or leave the car on an
incline when the engine is running.
NEUTRAL CLUTCH
The sprag assemblies keep the drive line from rotating
counterclockwise. However, for neutral and reverse, the
rear unit must rotate in a counterclockwise direction. This
is accomplished by means of a neutral clutch.
The neutral clutch operates as a connection between the
outer race of the rear sprag assembly and the transmission
case through the multiple disc clutch. When the plates are
applied, there is a solid connection between the race and
the case. When the clutch plates are released (reverse and
neutral) the connection is broken between the sprag clutch
and case. The sprag clutch is non-effective allowing the
rear unit to rotate counterclockwise for neutral and reverse.
OVERRUN CLUTCH
Reduction is obtained by holding one member of the front
and rear planetary gear sets from rotating counterclockwise
only. This is accomplished by the use of a sprag one-way
clutch. The held member is then free to rotate clockwise
even though the gear set is in reduction.
A condition might exist where the rear wheels would
drive the engine (Zero throttle downhill). In this case, the
power flow would be from the rear wheels to the output
shaft into the rear unit. Power flows from the rear unit
through the intermediate shaft to the drive torus. The
carrier of the front unit is attached to the torus and thus
becomes the drive member of the front planetary gear set.
The power flow in the front gear set would be reversed
with the input on the carrier, the internal gear held by the
engine, and the sun gear free to rotate clockwise at a faster
rate or overrun. This, in effect, would put the front unit
gear set in neutral condition.
To prevent the center gear from overrunning, a simple
disc called an overrun clutch is used, which operates when
overrun braking is needed (Drive 3 Range—Zero throttle).
The overrun clutch disc is splined to the driven torus
member in the front unit, which is also splined to the center
gear of the front unit.
The overrun clutch is actuated by an oil applied piston
and will compress the overrun clutch against spring pressure
locking the center gear to the case. This will retain the
front unit center gear from rotating counterclockwise or
overrunning.
GOVERNOR
The governor is located in the rear pump housing and is
driven by the rear pump driven gear which fits into the
governor tower. When the vehicle is started in motion, the
governor starts revolving.
Centrifugal force causes the governor plungers to move
away from the center. This opens a passage allowing oil to
flow into the regulated governor pressure lines. At the
same time, the regulated governor pressure exerts force on
the plungers to move them toward the center. Therefore,
we have governor to exhaust any pressure not required to
balance centrifugal force pressures that will vary with
vehicle or output shaft speed.
G-1 pressure rises faster than G-2 pressure, as the speed
increases, because the G-1 unit has greater weight than the
G-2 unit, therefore G-1 pressure will reach main line pressure
before G-2.
The G-1 weight has a one-pound spring holding the
weight in the open position to produce an initial G-1
pressure of five pounds per square inch. G-1 pressure is
directed to the G-5 valve, to the 2-3 governor valve, to the
3-4 shift valve, and the reverse blocker. G-2 pressure is
directed to the 2-3 shift valve and to the 3-4 governor valve.
FRONT PUMP
The front pump is a variable output vane type pump which
automatically regulates the output according to the need of
the transmission. It consists of the pump body, cover, slide,
rotor, seven vanes, two guide rings, and two priming
springs.
Output of the pump is controlled by the position of the
slide. The slide is held up by the priming spring for maximum
output when the pump is started. When the pump is
operating, the position of the slide is controlled by the
pressure regulator valve. When the output pressure is low,
the pressure regulator valve is pushed deep into its bore in
the pump, directing pressure below the slide to hold