DRIVE AXLE - TM-10-3930-623-120018

TM 10-3930-623-12

direct hydraulic pressure as required for either right or left turn

1-27. Additional oil from the pump is used by the control valve

assist. The spool is attached to the valve body at one end, and

to provide forward or reverse directional control to the vehicle.

through a torsion bar to the steering gear stub shaft at the

The control valve includes a pressure regulator valve, a brake

other end. Turning the steering wheel will steer the wheels

pedal operated inching valve, a forward and reverse clutch

without power assistance, through the torsion bar, spool and

supply valve, and a forward and reverse selector valve, with

valve body, until more than about three pounds pull at the rim

neutral position. These four valves are essentially in series in

of the steering wheel is required. At this amount of resistance

the control circuit. Regulated pump pressure is delivered to

the torsion bar twists, shifting the spool in the valve body, to

the inching valve, which can either deliver it through, or

valve hydraulic fluid as required to supplement steering effort

partially or completely shut off this pressure as the operator

in the direction in which the wheel is turned, as diagrammed in

requires, for inching operations while maintaining high engine

figure 1-6. Note that the rack-piston nut is geared directly to

speed for hoisting. Pressure on the brake pedal controls the

the pitman shaft. Power assistance is proportional to demand,

degree of clutch slippage for inching, while the position of the

and ceases when reduction in torsional load permits the torsion

selector valve determines which clutch will be engaged.

bar to return the valve spool to neutral. Hydraulic power is

taken from the truck main hydraulic pump via a pressure

1-28. DRIVE AXLE (See figure 1-9). This assembly is a

reducing priority valve on the main hydraulic pump, connected

double-reduction drive axle, bolted directly to the front of the

by tubing directly to the steering gear housing.

transmission. The output shaft of the transmission includes the

drive pinion gear which mates with the ring gear of the

1-22. STEERING AXLE ASSEMBLY (See figure 1-5). The

differential assembly to provide the first reduction. Internal

steering axle assembly is mounted on two neoprene blocks

gears at the outer end of the first drive axles drive sun gears to

located to permit a degree of movement to the axle necessary

give the second stage reduction to the final drive axles and the

to pass over irregular surfaces. The steering axle layout, and

wheels.

its relationship to the power steering system is shown in figure

1-5.

1-29. The hydraulic brake assemblies at each wheel are pedal

actuated as service brakes and handle operated by

1-23. Two equal length tie rods connect a center-mounted

mechanical linkage as parking brakes. A self-adjusting feature

bellcrank to each of the steering knuckles. Steering axle king

eliminates periodic adjustment to compensate for lining wear.

pins are mounted in true vertical position to provide similar

The brake master cylinder is a conventional automotive type,

steering characteristics in either forward or reverse travel. The

connected to a wheel cylinder at each front wheel by hydraulic

pneumatic tired wheels of the steering axle are not fitted with

lines. The service brake shoes serve also as parking brakes,

brakes.

being actuated by linkage from the hand brake lever next to the

operator's seat. The operator can adjust any slack from the

1-24. TRANSMISSION (See figures 1-7 and 1-8). The

parking brake linkage by turning a knurled knob at the top of

transmission is a power-shifted single ratio forward and

the parking brake lever.

reverse unit. A torque converter transmits engine output to the

transmission input shaft. The transmission is mounted directly

1-30 UPRIGHT CARRIAGE AND FORK ASSEMBLY (See

to the engine and drive axle. No intervening drive shaft is

figure 1-10). The upright carriage and fork assembly consists

used. Shifting between forward and reverse is accomplished

of four main items which are described in the following

by engagement of either a forward or reverse wet clutch in the

paragraphs.

unit. These clutches are engaged by hydraulic pressure

selected by a control valve.

1-31. OUTER UPRIGHT. This item is a welded one-piece

assembly attached to the frame of the vehicle. It encloses the

1-25. The clutches are contained in one large balanced drum

hydraulic hoist cylinder and inner upright assembly. The outer

assembly, and the plates drive concentric shafts. The outer

upright is pivot mounted on the frame to permit tilting by the tilt

shaft has a gear mounted on it which is in direct mesh with the

cylinder of the entire carriage and fork assembly as necessary.

output gear on the output shaft. This transmits forward rotation

to the output shaft. A gear on the inner shaft drives the output

1-32. INNER UPRIGHT. This item is a one-piece welded

shaft through an idler gear to give reverse drive. The main

assembly mounted within the outer upright. The hydraulic

case is of two piece construction and the rear half contains a

hoist cylinder, mounted in the base of the outer upright, is

heavy diaphragm midwall which forms one side of a straddle

attached at the top to the inner upright crossmember. The

mounting for the output gear and shaft. Oil passages are

inner upright is raised by the hydraulic cylinder.

internal except for the lines to the transmission oil cooler. The

oil supply is common for the torque converter, transmission,

1-33. CROSSHEAD ASSEMBLY. The crosshead assembly is

and drive axle, including the drive wheel bearings.

mounted on the top end of the hoist cylinder primary plunger.

Chains, secured at one end to the hoist primary cylinder, pass

1-26. An internal gear pump driven by the torque converter

over rollers on the crosshead assembly and are secured to the

hub supplies oil to the torque converter through a metering

lift carriage assembly. Raising the hoist cylinder primary

orifice and to a control valve assembly in the transmission

plunger raises the crosshead assembly to hoist the lift carriage

housing. Oil delivered to the torque converter maintains

and forks by the chain.

circulation through the converter to the oil cooler, or heat

exchanger in the engine radiator.

1-6