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 65 of 323
PAR
34-3 7
OPERATION OF HYDRAULIC SYSTEM S
CHAP
2,
SEC
I V
d . In fourth gear, main pressure is di-
rected to the top of the high knockdown plug.
Pressure at this point pushes the high knock-
down p1ug downward against the top of the
main-pressure regulator valve. There is no
effect on main pressure when lockup is en-
gaged because lockup apply pressure (main)
is already exerting an equal downward force
on the main-pressure regulator valve. How-
ever, if the lockup clutch should disengage,
the high knockdown plug would continue to push
downward
on
the
main-pressure
regulator
valve. Thus, main pressure is the same in
fourth gear whether operation is lockup or
converter. This is the only gear in which this
is true.
In all other gears, lockup operation
causes a lowering of main pressure.
35. HYDRAULIC SYSTEM FUNCTION –
REVERSE 1 GEAR (fig. 11)
Note . Refer to par. 51 and fig. 27
for the torque path through the power
train.
a.
Hydraulic system conditions in re-
verse 1 gear are the same as described for
neutral in par. 30, above, and illustrated in
fig. 6, except that the reverse-range clutch is
engaged and the vehicle is moving in reverse.
b . When the manual selector valve is in
reverse 1 position, the reverse-range clutch
is engaged and a branch of the clutch apply
line directs main pressure to the lower end of
the regulator plug. This pressure pushes up-
ward on the regulator plug which, in turn,
pushes upward on the main-pressure regulator
valve. Thus, the plug’s upward force assists
the regulator valve springs and increases main
pressure .
c . At higher speeds, the shift inhibitor
plunger wi11 extend and block any shift to
neutral or a forward gear.
d . In reverse gear, the brake coolan t
pump rotates in a reverse direction. Thus,
no brake coolant can be pumped.
36. HYDRAULIC SYSTEM FUNCTION –
REVERSE
2 GEAR (fig. 12)
Note . Refer to par. 52 and fig. 28
for the torque path through the power
train.
a.
Hydraulic system conditions in re-
verse 2 gear are the same as those for reverse
1 gear except that the power train output drive
is through the output clutches rather than
through the geared steer clutches.
b . In reverse 2 gear, no signal pressure
exists under the drive clutch relay valve .
Spring pressure holds the valve downward, in
which position steer pressure is directed to
the right- and left-output clutches. Reverse
2, third and fourth signal pressure is directed
to the lower side of the steer relay valve. This
pushes the valve upward against spring pres-
sure and alines the steer circuit for geared
steer.
37. HYDRAULIC SYSTEM FUNCTION -
LOW RANGE, STEER
a . First Gear, Full-right Steer
(fig. 13)
Note . Refer to par. 53 and fig. 29
for the torque path through the power
train.
(1) The hydraulic system will function in
first-gear steer in the same manner as de-
scribed for first-gear straight travel in par.
31, above, except for the position of the steer
valves and the flow of oil to the drive clutches
and brakes.
(2) In right steer, the steer control shaft
is rotated clockwise. This rotation moves the
right- steer valve downward while the left-steer
valve moves upward. The downward move -
ment of the right-steer valve blocks the flow
of steer pressure (in the upper passage), pre-
venting its being directed to the right-drive
clutch feed line. In the lower steer pressure
passage, a port is uncovered which allow s
steer pressure to enter the steer regulator
valve bore and to flow to the right-steer feed
line. The pressure in the right-steer feed line
is regulated by the action of the lower part of
the steer valve assembly. When steer pres-
sure
enters
the
right-steer
valve
bore,
it
exerts an upward pressure on the steer regu-
lator valve. Upward movement of the steer
regulator valve throttles the in-flow of steer
pressure .
Thus,
the
degree
of
downward
movement of a steer valve determines steer
3 5
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