POWER SHIFT HYDRAULIC SYSTEM

TM 10-3930-644-14&P

producing additional torque multiplication. When the

the oil on the end of the pressure regulator valve

output torque becomes high enough, the turbine starts to

overcomes the spring force and moves the regulator

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

valve to a position where main line oil is fed to converter

and its speed approaches the impeller speed, there is no

circuits. Feeding mainline oil into the converter circuit

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

lowers line pressure and permits the spring force to

the turbine. At this point the unit becomes a fluid

balance the force from the oil on the end of the regulator

coupling since there is no longer any torque

valve, thus regulating line pressure.

Oil from the

multiplication.

regulator valve is fed through an external tube to bypass

converter feed orifice to provide greater oil flow through

POWER SHIFT HYDRAULIC SYSTEM:

converter and cooler circuit.

The transmission hydraulic system consists of the torque

Inching Valve

converter, a hydraulic pump, the control valve and the

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

clutch pack.

will regulate the clutch maximum pressure, determined

by the spring or springs used in this location.

Control Valve

Depressing the inching pedal permits the plunger to

The control valve is mounted on the transmission

move away from the spring, decreasing spring's effect

housing and forms the top closure of the gear case.

on the inching valve to lower clutch pressure. Clutch

Machined porting plates are attached to the bottom of

pressure can be varied from 0 to maximum pressure

the valve to eliminate external piping. Passages in the

obtainable from the spring combination in the valve body

plates align with passages drilled or cast into the

assembly. Clutch pressure regulated by the inching

transmission housing.

valve is less than the pressure regulated by the regulator

valve. Pressure recommendations for your particular

Clutch Pack

model should be obtained from the equipment

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

manufacturer.

reverse clutch, and pistons and cylinders The clutches

are engaged by oil pressure applied behind the clutch

Clutch Supply Valve

pistons, which causes engagement within the drum.

Line pressure on the end of clutch supply valve moves

valve against spring force and permits oil to feed from

Oil Pump

the inching valve to manual valve. The high and low

The gear type oil pump provides hydraulic pressure for

gear cam operated valve can exhaust oil from the end of

the converter and clutch pack. It is directly driven from

the clutch supply valve faster than it can be replaced

the input side of the converter. Since the converter is

through the feed orifice. Therefore, the spring force

mounted on the flywheel, the pump is in operation

returns the valve to the blocking position. in the blocking

whenever the engine is running. This means that there

position, neither clutch can be fed and both clutches are

is hydraulic pressure even with the engine idling.

exhausted at the clutch supply valve, thus causing a

neutral condition to exist in the transmission.

Hydraulic oil enters the pump through the intake screen

and case passages. Oil leaving the pump is directed

NOTE

through case and adapter passages to all open valve

Latest Allis-Chalmers models have

body passages and through an orifice to convertor. The

eliminated the seat dump valve in

orifice acts to drop pressure of the oil entering the

favor of a mechanical system which

converter. Oil leaving the converter is fed through cooler

returns the selector valve to neutral.

and cooler bypass valve. The bypass valve remains

As a result of this the external control

closed unless the pressure exceeds the valve opening

passage of the clutch supply valve is

limits. Oil returning From the cooler is directed to clutch

plugged and there is no way to bleed

cooling and lube circuit.

pressure from the pilot section of the

valve.

The valve will shift into

Pressure Regulator Valve

operating position when the engine

starts, and will stay in that position

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

as long as the engine is running. The

increasing in pressure and continues to increase until

valve no longer provides a useful

the force from

function and is retained as part of the

control valve for purposes of

standardization with the two speed

transmission.

R-171-1

3-117