Pontiac FIREBIRD 1972 Service Manual page 909

TURBO HYDRA-MATIC (M-40) TRANSMISSION
7E- 19
FRONT SERVO
Fig. 7E-16 Drive Range
-
Second Gear
Servo oil and the servo release spring prevents the apply
of the band in second gear, Drive range, when intermedi-
ate clutch apply oil is directed between the servo and
accumulator pistons. Servo oil is also present in Neutral
and Reverse ranges.
DRIVE RANGE
-
SECOND GEAR
Servo oil charging the accumulator is present in first and
second gears and has the servo and accumulator pistons
stroked down against the accumulator spring (Fig. 7E-
16). In second gear, intermediate clutch oil is directed
between the servo and accumulator pistons but does not
separate the pistons, as the force of servo oil holding the
piston down is equal to the force of intermediate clutch oil
attempting to stroke the servo piston up.
DRIVE RANGE
-
THIRD GEAR
Direct clutch pressure rises to a value such that the force
from it, plus the accumulator spring force, overcomes the
force from the servo pressure and moves the accumulator
piston to the stop on the accumulator piston pin. This, in
turn, strokes the servo piston the same amount of travel
which allows it to just contact the band apply retainer ring
on the servo pin, but it will not move the pin to apply the
band.
The stroking of the accumulator piston absorbs some di-
rect clutch oil and permits the direct clutch to apply at a
controlled rate for a smooth 2-3 shift.
FRONT SERVO
Fig. 7E-17 Drive Range
-
3-2 Shift
smooth transfer of the drive load to the intermediate sprag
(Fig. 7E-17). The controlled release pressure lets the en-
gine increase its rpm for the lower gear ratio of second
gear during detent downshifts, resulting in a shift and
better acceleration.
Servo oil seats a check ball, intermediate clutch oil seats
another check ball and oil must pass through the two
orifices which slows the stroking of the servo and ac-
cumulator pistons. The exhausting direct clutch oil from
the accumulator seats a third check ball and the exhaust-
ing direct clutch oil passes through an orifice which con-
trols the clutch pressure during the direct clutch release.
SUPER RANGE
-
SECOND GEAR
Intermediate clutch oil from the 1-2 shift valve seats the
check ball and passes through an orifice to apply the front
band. The pressure applying the band is also controlled by
the stroking of the accumulator piston which is moved by
orificed flow of intermediate clutch oil and resisted by the
accumulator spring and exhausting orificed direct clutch
oil in a manual downshift 3-2 for a smooth apply of the
band for Super range engine braking.
The rear servo applies the rear band for overrun engine
braking in Lo range, first gear. It applies the band in
Reverse to hold the reaction carrier to provide the reverse
gear ratio.
On the 1-2 shift in Drive and Super ranges, it serves as an
accumulator for the intermediate clutch to provide a
smooth shift.
DRIVE RANGE
-
3-2 SHIFT
DRIVE AND SUPER RANGE-FIRST GEAR
The release of the direct clutch is controlled by the front
servo, three orifices and three check balls to allow a In first gear, Drive and Super ranges, 1-2 accumulator oil