TM-9-2520-234-35
POWER TRAIN ASSEMBLY; ALLISON MODEL XTG411-2A
TECHNICAL MANUAL; FIELD AND DEPOT MAINTENANCE MANUAL
JULY 1962
TM-9-2520-234-35 - Page 61 of 323
PAR
31-34
OPERATION OF HYDRAULIC SYSTEM S
CHAP
2,
SEC
I V
are open. The brake coolant pump is operat-
ing but air is being drawn through the open air
valves and directed to the brakes. If the brakes
are applied (except hydraulically in steering),
the air valves close and oil is drawn from the
sump, through check valves, and delivered to
the brake plates.
d . Fig. 7 illustrates partial opening of
the throttle which produces TV pressure at the
throttle regulator valve. Refer to par. 30f, g ,
h , and i , above, for a complete explanation of
the function of the throttle and throttle regu-
lator valves.
32.
HYDRAULIC SYSTEM FUNCTION -
SECOND GEAR (fig. 8)
Note . Refer to par. 48 and fig. 24
for the torque path through the power
train.
a . The function of the hydraulic system
in second gear is the same as that in first
gear except that drive to the power train out-
puts is through the output clutches rather than
through the geared steer clutches.
b . When the manual selector valve i s
shifted to the second gear position, the low-
range clutch is engaged but no signal pressure
is present. Because no signal pressure exists,
the drive clutch relay valve is held downward
by the spring at its upper end. This alines the
hydraulic system to direct steer pressure to
the right- and left -output clutches.
c . Fig. 8 illustrates the lockup shift valve
in its downward position and shows main pres-
sure applying the lockup clutch. Note th e
branch of the lockup clutch line that directs
pressure to the top of the main-pressur e
regulator valve.
Downward movement of the
valve exhausts oil to the sump, reducing main
pressure .
Note . If pump speed is not sufficient
to provide a larger volume of oil than
that flowing to the converter and lost
by leakage, the main-pressure regu-
lator valve may not move downward
sufficiently to exhaust oil.
d . At higher speeds, the shift inhibitor
plunger is extended and prevents shifting to
first, neutral or reverse gears.
33. HYDRAULIC SYSTEM FUNCTION -
THIRD GEAR (fig. 9)
Note . Refer to par. 49 and fig. 25
for the torque path through the power
train.
a . In third gear, the hydraulic system
operates as in second gear except that main
pressure applies the intermediate-range clutch
and that reverse 2, third and fourth signal
pressure is directed to the lower end of the
steer relay valve.
b . When the manual selector valve is in
third-gear position, the intermediate-range
clutch is charged and signal pressure is di-
rected to the steer relay valve. Signal pres-
sure pushes the valve upward against spring
pressure and a1ines the steer circuit fo r
geared steer.
c . At higher speeds, the shift inhibitor
plunger wi11 extend and prevent shifting to
lower gears, neutral and reverse gears.
34. HYDRAULIC SYSTEM FUNCTION –
FOURTH GEAR (fig. 10)
Note . Refer to par. 50 and fig. 26
for the torque path through the power
train.
a .
Conditions in the hydraulic system
during fourth-gear operation are the same as
in third gear except that the high-range clutch
is engaged instead of the intermediate-range
clutch. The only valve at a different position
is the manual selector valve.
b . When in the fourth gear position, the
manual selector valve lever will permit the
shift inhibitor plunger to extend, at higher
speeds, and block any shift from fourth gear.
c.
Full-throttle opening is illustrated,
showing how both T and TV pressures are pro-
duced. Note that T pressure is equal to maxi-
mum TV pressure but that T pressure is di-
rected to a different area.
3 1
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