CHAPTER 2 OPERATING INSTRUCTIONS - TM-55-1740-200-140019

TM 55-1740-200-14

CHAPTER 2

OPERATING INSTRUCTIONS

reverse speed. S e c o n d through fifth gears are

2-1. INTRODUCTION.

synchronized. Gear selection is made manually by the

gearshift lever located in the cab.

2-2. This chapter contains operating instructions for the

Type MB-4 towing tractor. The principles of operation

2-10. TRANSFER CASE. The transfer case transfers

precede the operating instructions to provide easier

transmission output to the front and rear axles with gear

understanding of the tractor operation.

reduction. The transfer case i s equipped with a

differential which may be manually locked in or locked

2-3. PRINCIPLES OF OPERATION.

out, depending on road conditions. When one axle loses

traction the differential action may be locked out which

2-4. The operating principles and basic fundamentals

provides the effect of locking the output shafts together

with which the operator is familiar have been omitted.

to transmit identical rpm to each axle. Differential action

O p e r a t i n g procedures of the more complicated

is controlled manually by a lever in the cab and should be

components and systems are explained in the following

used only under slippery road conditions. Because of the

paragraphs.

differential, the vehicle is in 4-wheel drive at all times.

2-5. ENGINE. The engine operation is the same as any

2-11. AXLES. Propeller shafts connect the identical

standard, flat-head, six cylinder, internal combustion

front and rear axles to the transfer case. Each axle is

engine.

equipped with a standard differential and heavy duty

steerable type wheels. The wheels encase the wheel brake

2-6. FUEL SYSTEM. Engine fuel is provided by a

assemblies and provide a mounting surface for the tire

standard fuel system and regulated by a velocity type

assembly.

governor. The governor is an integral part of the

carburetor and regulates fuel supply by closing the

2-12. STEERING SYSTEM. The hydraulic steering

throttle valve when fuel-air mixture velocity exceeds the

system (figure 2-1) is powered by the engine driven

governor setting.

hydraulic pump (1) which pumps fluid from the reservoir

2-7. HYDRAULIC TRANSMISSION. The hydraulic

(2) directly to the front control valve (9). The front

t r a n s m i s s i o n transfers torque to the mechanical

control valve directs fluid to the front cylinder (8) when

transmission through an integral fluid coupling. During

actuated by the steering wheel (3) and bypasses all other

normal driving the hydraulic transmission input and

fluid to the flow divider (5). The flow divider sends a

output rpm are the same. During heavy pulling the output

maximum of 30 psi to the rear control valve (6), all over

rpm is much slower than the input rpm. Under these

30 psi is returned to the reservoir. The rear control valve

conditions the hydraulic transmission has multiplied

directs fluid to the rear cylinder (7) when actuated by the

torque to transfer full engine power to the transmission

rear wheel steering lever (4). When the steering lever is

and prev!ent engine stall. The hydraulic transmission fluid

released, the rear wheels automatically return to the

is cooled by circulation through a heat exchanger located

straight ahead position. Although the front and rear

in the radiator.

control valves are hydraulically connected, front and rear

control are completely independent.

2-8. CLUTCH. Fluid under pressure is available to the

clutch at all times. When the solenoid control switch,

2-13. BRAKE SYSTEM. The hydraulic brake system

located on the gearshift knob, is pressed the solenoid

(figure 2-2) is a standard hydraulic system equipped with

opens a spool valve. With the valve open, oil circulates

a vacuum booster unit (6). The booster unit is connected

through and disengages the clutch to allow manual

to the intake manifold to obtain the vacuum necessary

selection of transmission gears.

for proper operation. When the brake pedal (3) is

depressed the master cylinder (2) hydraulically opens the

2-9. TRANSMISSION. The transmission is a mechanical

air intake valve on the booster unit. When the valve

synchro-mesh unit with five forward speeds and one

opens, air enters the booster unit through the air cleaner

2-1