Pontiac FIREBIRD 1972 Service Manual page 911

TURBO HYDRA-MATIC (M-40) TRANSMISSION
7E-2 1
LO RANGE
-
SECOND GEAR
In second gear, the rear band is released (Fig. 7E-21).
Intermediate clutch oil is directed to the release side of the
servo piston which, with line oil in the 1-2 accumulator
passage, balances out the Lo range oil on the apply side
of the servo piston and the servo release spring strokes the
servo piston to the released position.
REVERSE
In Reverse, the rear band is applied to hold the reaction
carrier. Reverse oil is directed to the servo piston to apply
the band. To insure the band holding the reaction carrier
for the reverse gear ratio, line pressure is increased in
Reverse and no other oil pressures are present in the servo
to resist the apply of the servo piston.
1-2 ACCUMULATOR
1-2 Accumulator oil charges the rear servo accumulator
in first gear in preparation for the apply of the intermedi-
ate clutch on the 1-2 shift.
The valve train consists of a 1-2 accumulator valve, a 1-2
accumulator primary valve and two springs.
1-2 Accumulator oil pressure is used to obtain greater
flexibility in attaining the desired curve for various engine
requirements.
Drive oil is directed to the 1-2 accumulator valve and is
regulated by the valve train to 1-2 accumulator oil.
Modulator pressure is directed to the 1-2 accumulator
primary valve and the 1-2 accumulator valve. This results
in 1-2 accumulator pressure being engine torque conscious
and adjusts for smooth, durable shifts according to engine
torque output.
For clutch durability, detent oil is directed to the 1-2
accumulator primary valve to raise 1-2 accumulator pres-
sure during detent 1-2 shifts. Lo range oil is directed to the
1-2 accumulator valve, during Lo range operation, to raise
1-2 accumulator pressure to line pressure. This increased
pressure, directed to the rear servo accumulator piston,
resists servo apply pressure and slows down the apply of
the rear band for a smooth manual shift to Lo range, first
gear.
DETENT AND DETENT REGULATOR
VALVES
When the accelerator pedal is fully depressed, the detent
valve train replaces the modulator as a controller of shift
points.
Line pressure is fed through a small orifice to one end of
I
M O D . D R I V E
I I L - l I
MOD. DETENT
1
v p e * E x t i .
I I
LO
DETENT
I
SOLENOID
I
Fig. 7E-22 Detent Solenoid Needle Valve Closed
-
Normal
Operation
the detent valve (Fig. 7E-22). In normal throttle operat-
ion, the cavity at this end of the valve is sealed by the
needle valve in the detent solenoid assembly. This line
pressure holds the detent valve train in an inoperative or
normal position.
When the throttle is opened wide, an electric switch on
throttle linkage is closed which energizes the detent solen-
oid (Fig. 7E-23). The needle valve is opened by the solen-
oid, causing a pressure drop on the end of the detent valve.
The detent regulator valve spring then shifts the detent
valve and allows the detent regulator to regulate detent oil
to a fixed pressure of approximately 70 psi. When the
detent valve shifts, it routes this fixed or detent pressure
I
I I
I
i o b
OETENT
LO
E X H .
DETENT
I
SOLENOID
I
Fig. 7E-23 Detent Solenoid Needle Valve Open
-
Solenoid
Energized
I
MOD. D R I V E
I I
. .
MOD. DETENT LO
DETENT
I I
SOLENOlD
I
Fig. 7E-24 Detent Solenoid Needle Valve Closed
-
Lo Range
Operation