Figure 2. Self-Adjusting Brakes (Typical)

TM 10-3930-644-14&P

1. Operation of Wheel Cylinders and Brake Shoes:

The first requisite for safe, sure hydraulic

braking is the use of high quality brake fluid.

The hydraulic brake system requires a "solid

column of fluid" and the fluid should possess

essential protective properties which safeguard

the system.

CAUTION

Use only a premium quality, heavy-

duty brake fluid with an extreme

"heat-cold" range. SAE specification

R-71 is recommended.

Hydraulic fluid entering the wheel cylinders -from

the master cylinder forces pistons to move

individually and in opposed directions. This

piston travel expands the brake shoes. As the

pressure increases, the piston cup lips are

forced more tightly against the cylinder wall,

effecting a positive fluid seal, neglecting minor

friction looses; the controlled actuating force is

Figure 2. Self-Adjusting Brakes (Typical)

equal to and varies with the hydraulic pressure

exerted against each square inch of the piston

attached to the brake shoes with roll pins, and the pin

face.

mounting holes in the brake shoes are 1/32" oversize to

The pistons are returned to an "off"' position by

provide proper working clearance between the shoe

the force of the brake shoe retracting springs.

lining and brake drum.

The piston cup lips are pressed against the

cylinder walls by natural resiliency and system

CAUTION

residual pressure to seal against fluid or air

If link is not operating properly,

leaks.

The hydraulic pistons of the wheel

install new link assembly. Links are

cylinders follow the brake shoes as they expand

factory-set and must not be adjusted

into the drums.

in the field.

TOPIC 2. MASTER CYLINDER

Figure 3. Master Cylinder Assembly

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