Pontiac FIREBIRD 1972 Service Manual page 908

7E- 18 1972 PONTIAC SERVICE M A N U A L
Fig. 7 E - 1 3 2-3 Shift Valve
Fig. 7 E - 1 4 3-2 Shift Valve
14. Rear Servo and Accumulator. The rear servo and
accumulator assembly serves three functions:
a. The band apply piston provides the band apply
force to hold the rear band in reverse.
b. The band apply piston provides the band apply
force for overrun band apply in Lo range, 1st
gear.
c. The accumulator piston, in conjunction with 1-2
accumulator oil, provides the accumulator func-
tion for the apply of the intermediate clutch.
15. Front Servo. The front servo serves two functions:
a. Intermediate clutch oil applies the front servo to
apply the front band in second gear in Super and
Lo Range.
b. During a 2-3 shift, direct clutch oil utilizes the
servo and accumulator pistons as the accumula-
tor for direct clutch apply.
FRONT SERVO
OPERATION
The front servo applies the front band to provide engine
braking in 2nd gear in Super and Lo ranges. It is also used
as an accumulator for the apply of the direct or 3rd clutch
and in conjunction with a series of check balls and con-
trolling orifices as a part of the timing for the release of
the direct or 3rd clutch.
T o prevent the apply of the front band in Neutral, Drive
and Reverse ranges, oil is directed from the manual valve
to the release side of the servo piston.
In Drive range, the servo release oil from the manual valve
is used to charge the servo in preparation for the apply of
the direct clutch.
Direct clutch oil is directed to the front servo accumulator
piston where spring force, plus 3rd clutch pressure,
strokes the piston up against the force of servo release oil.
This lowers the clutch apply pressure for a smooth en-
gagement.
The release of the direct clutch and the exhausting of the
front servo accumulator is slowed down bv three check
balls and three orifices which permits a sof; return of the
drive load to the intermediate sprag and also allows engine
rpm to increase during a detent 3-2 downshift in prepara-
tion for the lower gear ration, which results in a smooth
shift.
DRIVE RANGE
-
FIRST GEAR
Servo oil from the manual valve in Drive range charges
the accumulator by stroking the servo and accumulator
pistons against the accumulator spring (Fig. 7E- 15). This
prepares the accumulator for the controlled apply of the
direct clutch on a 2-3 shift. The charging of the accumula-
tor in Drive range, first gear, also makes it possible to have
a controlled 1-3 let up shift as the accumulator is prepared
in first gear for direct clutch apply.
FRONT SERVO
Fig. 7E-15 Drive Range
-
First Gear