POWER SHIFT HYDRAULIC SYSTEM:

TM 10-3930-644-14&P

producing additional torque multiplication. When the

the regulator valve to a position where main line oil is fed

output torque becomes high enough, the turbine starts to

to converter circuits. Feeding mainline oil into the

turn and the truck will move. As the turbine speeds up

converter circuit lowers line pressure and permits the

and its speed approaches the impeller speed, there is no

spring force to balance the force from the oil on the end

longer any reaction on the stator and it starts to turn with

of the regulator valve, thus regulating line pressure. Oil

the turbine. At this point the unit becomes a fluid

from the regulator valve is fed through an external tube

coupling since there is no longer any torque

to bypass converter feed orifice to provide greater oil

multiplication.

flow through converter and cooler circuit.

POWER SHIFT HYDRAULIC SYSTEM:

Inching Valve

The transmission hydraulic system consists of the torque

The inching valve, when the inching valve plunger is in,

converter, a hydraulic pump, the control valve and the

will regulate the clutch maximum pressure, determined

clutch pack.

by the spring or springs used in this location.

Depressing the inching pedal permits the plunger to

Control Valve

move away from the spring, decreasing spring's effect

on the inching valve to lower clutch pressure. Clutch

The control valve is mounted on the transmission

pressure can be varied from 0 to maximum pressure

housing and forms the top closure of the gear case.

obtainable from the spring combination in the valve body

Machined porting plates are attached to the bottom of

assembly. Clutch pressure regulated by the inching

the valve to eliminate external piping. Passages in the

valve is less than the pressure regulated by the regulator

plates align with passages drilled or cast into the

valve. Pressure recommendations for your particular

transmission housing.

model should be obtained from the equipment

manufacturer.

Clutch Pack

Clutch Supply Valve

The clutch pack consists of a drum, a forward and a

reverse clutch, and pistons and cylinders. The clutches

Line pressure on the end of clutch supply valve moves

are engaged by oil pressure applied behind the clutch

valve against spring force and permits oil to feed from

pistons, which causes engagement within the drum.

the inching valve to manual valve. The high and low

gear cam operated valve can exhaust oil from the end of

Oil Pump

the clutch supply valve faster than it can be replaced

through the feed orifice. Therefore, the spring force

The gear type oil Pump provides hydraulic pressure for

returns the valve to the blocking position. In the blocking

the converter and the clutch pack. It is directly driven

position, neither clutch can be fed and both clutches are

from the input side of the converter. Since the converter

exhausted at the clutch supply valve, thus causing A

mounted on the flywheel, the pump is in operation

neutral condition to exist in the transmission.

whenever the engine is running. This means that there

is hydraulic pressure even with the engine idling.

NOTE

Latest Allis-Chalmers models have

Hydraulic oil enters the pump through the intake screen

eliminated the seat dump valve in

and case passages. Oil leaving the pump is directed

favor of a mechanical system which

through case and adapter passages to all open valve

returns the selector valve to neutral.

body passages and through an orifice to convertor. The

As a result of this the external control

orifice acts to drop pressure of the oil entering the

passage of the clutch supply valve is

converter. Oil leaving the converter is fed through cooler

plugged and there is no way to bleed

and cooler bypass valve. The bypass valve remains

pressure from the pilot section of the

closed unless the pressure exceeds the valve opening

valve.

The valve will shift into

limits. Oil returning from the cooler is directed to clutch

operating position when the engine

cooling and lube circuit.

starts, and will stay in that position

as long as the engine is running. The

Pressure Regulator Valve

valve no longer provides a useful

function and is retained as part of the

Oil from the pump, after filling all open circuits, begins

control valve for purposes of

increasing in pressure and continues to increase until

standardization with the two speed

the force from the oil on the end of the pressure

transmission.

regulator valve overcomes the spring force and moves

M-171-1

2-51