Pontiac FIREBIRD 1972 Service Manual page 1049

TURBO HYDRA-MATIC (M-38) TRANSMISSION 7G-11
CONVERTER ASSEMBLY
SUN GEAR & DRIVE SHELL
CONVERTER PUMP
INTERMEDIATE
(
1 - 2
)
CLUTCH INPUT R I N G GEAR
OUTPUT CARRIER
L O W 6 REVERSE
ROLLER CLUTCH
OUTPUT SHAFT
G O V E R N O R
-
DRIVEN GEAR
VALVE B O D Y
PUT R l N G GEAR
INTERMEDIATE O . R .
ROLLER CLUTCH & REVERSE CLUTCH
LOIL PUMP COVER
LLow a
REVERSE CLUTCH SUPPORT
O I L PUMP B O D Y
Fig. 7G-5 Cross Section of Transmission
2. Engine Vacuum
-
To operate the vacuum modulator.
3. Cable Control
-
To operate the detent valve.
A vacuum modulator is used to automatically sense any
change in the torque input to the transmission. The
vacuum modulator transmits this signal to the pressure
regulator, which controls line pressure, so that all torque
requirements of the transmission are met and smooth
shifts are obtained at all throttle openings.
The detent valve is activated by a cable that is connected
to the accelerator lever assembly. When the throttle is half
open, the valve is actuated causing throttle downshift at
speeds below 50 mph. When the throttle is fully open, the
detent valve is actuated causing the transmission to down-
shift from 3-1 at speeds below 40 mph and 3-2 below 75
mph.
POWER FLOW
In neutral or park, all clutches and the intermediate over-
run band are released. Also, in park range the parking
pawl is engaged, preventing movement of the vehicle.
Therefore, no power is transmitted from the torque con-
verter turbine to the planetary gear sets or output shaft
(Fig. 7G-6).
With the range selector lever in Drive (D) range, the
forward clutch is applied. This delivers turbine torque
from the input shaft through the forward clutch to the
input ring gear in a clockwise direction (converter torque
ratio equals approximately 2.25 to 1 at stall).
Clockwise rotation of the input ring gear causes the output
planet pinions to rotate in a clockwise direction, driving
the sun gear (and shaft) counterclockwise. In turn, the sun
gear turning counterclockwise will cause the output ring
gear and output shaft to turn in a clockwise direction (in
a reduction ratio of approximately 2.52 to 1). The reaction
of the reaction carrier planet pinions against the output
ring gear is taken by the low and reverse roller clutch,
which is grounded to the case (Fig. 7G-7).
To prepare the transmission for the shift into second gear,
the intermediate roller clutch is locked. Therefore, the sun
gear, sun gear drive shell, direct clutch housing, inter-
mediate roller clutch and the intermediate clutch faced
plates are all turning in a counterclockwise direction.