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Drive. However, hydraulic action differs in that the manual
valve in the main valve body is so positioned that it blocks off
the passages to the low-drive shift valve. In addition, it supplies
pressure to the modulator exhaust, which has the effect of
increasing mainline pressure.
Revers
in Keverse it is necessary to turn the planet carrier, which
is part of the output shaft, in a direction opposite to that of
the input shaft (Fig. 4PG). With the selector lever in the
reverse position, the clutch and low band are released and the
reverse clutch is applied holding the ring gear in a stationary
position. Drive then, is through the input shaft and input sun
gear to the long pinions to the short pinions. Since the short
pinions are meshed with the reverse ring gear which is now
held stationary by the reverse clutch, the short pinions will
walk around inside the internal gear in a reverse direction
carrying the output shaft to which they are attached with
them at a reverse reduction of 1.82 to 1 or 1.76 to 1 depend
ing on engine application.
Neutral
Fig. 6PG-Powerglide Governor
In Neutral the output shaft remains stationary. With the
selector lever in the neutral position, the clutches and low
band are released, consequently there is no reaction member
to provide positive drive. All gears are free to spin around their
own axis and no motion is imparted to the planet carrier in
any direction.
Par
In Park, all reaction members are released so they are in
neutral. A positive geartrain lock is provided when the park
pawl is engaged with heavy teeth spaced around the front face
of the planet carrier. The linkage is actuated by direct manual
action, but the pawl is activated by spring action. Thus, if the
pawl is not directly in line with a tooth of the carrier, the
linkage remains in the park position with the spring holding
pressure against the pawl. Right rotation of the carrier will
then immediately seat the pawl and lock the output shaft to
the case.
CAUTION: Severe damage may occur if the unit is shifted
to park with the vehicle in motion.
The vacuum modulator is threaded to the rear face of the case
assembly and aligns to the valve bore in the upper section of
the valve body.
The lower section of the body contains a pressure regu
lator valve, a booster valve, a low-drive shift valve, and a low
drive regulator valve.
Downshift timing valve is contained in the oil pump. Also,
on units equipped with an oil cooler in the radiator, a cooler
by-pass valve is located in the oil pump which can open a path
to the lubrication circuit in case of a restriction in the cooler
system.
The governor (Fig. 6PG) is mounted on the output shaft.
Driving requirements are signalled by the driver and the
engine through three means: the manual valve, which is con
nected by linkage to the selector lever; the throttle and detent
valves, which are connected through linkage to the accelerator
pedal and indicate changes in throttle position; the vacuum
modulator which senses engine manifold vacuum as supplied
by a vacuum line. The remainder of the hydraulic system is
controlled by internal factors.
HYDRAULIC COMPONENTS
General Information
The main valve body (Fig. 5PG) of the Powerglide is
bolted to the under surface of the transmission case. It is
enclosed by the oil pan assembly and is completely accessible
with the transmission in the vehicle. All control valves are
located in the main body with the exception of two in the oil
pump (a third valve is used on vehicles equipped with an oil
cooler), and the governor valve.
The main valve body consists of two cast iron bodies
joined at a transfer plate. The upper section of the valve body
contains a manual valve, a detent valve, a throttle valve, a high
speed downshift timing valve, and a vacuum modulator valve.
Pressure Development and Control
Most of the valves and control members of the hydraulic
systems are interconnected in some manner and usually several
events are occurring at the same time. In order to avoid
confusion, each component's operation will be treated in a
step by step manner.
Oil Pump Circuit
The internal-external gear type oil pump is driven by the
converter hub. Pump drive is accomplished by two concentric
tangs, machined on the I.D. of the small gear, which engage
two matching slots in the converter hub. Since the converter is
bolted to the engine flywheel, the oil pump operates and pro
vides pressure any time the engine is running.
As the engine is started and the oil pump begins operating
