Pontiac FIREBIRD 1972 Service Manual page 906

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1972 PONTIAC SERVICE MANUAL
results in a smaller change in governor pressure .at low
speeds than at high speeds. Because of this characteristic,
a governor with a single set of weights has less pressure
change at low speed than at high speed. To increase the
pressure change of the governor signal at low speeds, the
flyweights are so designed that their effective mass is
greater at speeds below approximately 720 rpm than it is
above this speed.
This is done by arranging the primary weights so that they
act through preloaded springs on the secondary weights
which, in turn, act on the valve. At approximately 720
rpm, the centrifugal force on each primary weight exceeds
the spring force and the primary weights move to a
grounded stop. With the primary weights grounded, the
force on the governor regulator valve is equal to the spring
forces plus the centrifugal force on the secondary weights.
FUNCTIONS OF VALVES AND
HYDRAULIC CONTROL UNITS
1. Pressure Regulator:
a. Regulates line pressure according to a fixed
spring force and forces controlled by modulator
and reverse pressures (Fig. 7E-8).
b. Controls the flow of oil that charges the torque
converter, feeds the oil cooler and provides lu-
brication for the transmission.
2. Manual valve establishes the range of transmission
operation, i.e. P, R, N,
D, S, L, as selected by the
vehicle operator through the manual selector lever
(Fig. 7E-9).
3. Governor generates a speed sensitive oil pressure that
increases with output shaft or vehicle speed. Gover-
I
Fig. 7E-8 Pressure Regulator Valve
Fig. 7E-9 Manual Valve
nor pressure is used to vary the shift points and
modulator pressure regulation (Fig. 7E-10).
4. Modulator valve regulates line pressure to a
modula-
tor pressure that varies with torque to the transmis-
sion (Fig. 7E-11). It senses force created by:
a. The vacuum modulator bellows that increases
modulator pressure.
b. Engine vacuum acting on a diaphragm to de-
crease modulator pressure.
c. Governor pressure which is generated by the gov-
ernor assembly. Governor pressure tends to de-
crease modulator pressure.
5. 1-2 Shift valve controls the oil pressure that causes
the transmission to shift from 1-2 or 2-1. Its operation
is controlled by governor pressure, detent pressure,
modulator pressure and a spring force (Fig. 7E- 12).
6. 1-2 Regulator valve regulates modulator pressure to
a lesser pressure that is proportional to modulator
pressure, tending to keep the 1-2 shift valve in the
downshift position.
7. 1-2 Detent valve senses regulated modulator pressure
tending to hold the 1-2 shift valve in the downshift
position and provides an area for detent pressure for
detent 2-1 shifts.
8. 2-3 Shift valve controls the oil pressure that causes
the transmission to shift from 2-3 or 3-2. Its operation
is controlled by modulator, intermediate, governor
and detent pressure as well as a spring force (Fig.
7E- 13).
9. 2-3 Modulator valve senses modulator pressure to
apply a variable force proportional to modulator
pressure which tends to hold the 2-3 shift valve
downshifted.
10. 3-2 Valve shuts off modulator pressure from acting
on the shift valve trains after the direct clutch has
been applied. This allows fairly heavy throttle operat-
ion in third speed without downshifting. In third