MECHANICAL BRAKES
Page K-5
Repair and Service Manual
Read all of Section B and this section before attempting any procedure. Pay particular attention to all Notices, Cautions, Dangers and Warnings.
adjusters will function. Free pedal travel, pedal force,
shoe to drum clearance and braking capability are
closely related. It is very important to maintain the
proper relationships to assure braking performance and
the best wheel brake adjustment.
How the Service Brake Works
Depressing the service brake pedal pulls the compensa-
tor assembly and equalizer link, which are connected to
the brake cables (Ref Fig. 3). The first part of the pedal
travel removes slack from the system. Continued motion
of the brake pedal pulls both the left and right brake
cables. Each brake cable pulls a brake lever which
pushes the rear brake shoe against the brake drum.
When the rear shoe contacts the brake drum, it can no
longer move rearward. Additional pedal (and cable)
travel causes the actuator bracket (moving anchor) to
move and applies force to the front shoe, pushing it
against the brake drum. The force applied to the front
and rear shoes is approximately equal. As the shoes
contact the moving brake drum, the shoes try to move in
the direction of drum rotation. This movement results in
the typical brake shoe wear patterns.
Equalizer Link
The equalizer link balances braking between the driver
and passenger sides of the vehicle. Variations in wheel
brake adjustment, cable friction and manufacturing toler-
ances may cause the equalizer to be slightly misaligned.
This misalignment is normal.
Automatic Adjuster Mechanism
Never manually adjust the brakes at the star wheel. Doing
so will cause permanent damage to the adjuster assem-
bly and result in a gradual loss of brakes.
The wheel brakes are equipped with an automatic
adjuster mechanism that is designed to compensate for
brake shoe wear and eliminate the need for manual
brake shoe adjustment. Do not manually adjust the
brakes by prying back the adjuster arm and turning the
star wheel. Permanent damage to adjuster will result.
Adjustment takes place only when the brake is fully
applied and released
while the vehicle is moving
Fig. 4). It is very important that the brake cables permit
the brake levers to release fully when the brake pedal is
in the released position.
How the Parking Brake Works
The parking brake is operated by a smaller pedal which
extends across the top of the service brake pedal. It is
attached to the service brake pedal with a hinge pin and
is spring loaded (Ref Fig. 5).
Depressing the parking brake pedal moves the latch arm
against the catch bracket attached to the chassis. As the
parking brake is depressed, the service brake is applied
until the notch in the latch arm engages with the catch
bracket. The service brake pedal is held in the applied
(down) position by the catch bracket. The latch arm is
Fig. 4 Wheel Brake Adjustment
A
C
Brakes adjust only while the vehicle is moving.
When the brake pedal is depressed, the brake lever
moves toward the front of the vehicle (A).
The other end of the brake lever moves to the rear of the
vehicle (B) where it contacts the brake adjuster arm,
causing it to move.
The brake adjuster arm moves away from the star wheel
(C). The amount of adjuster travel is limited by the amount
of brake shoe travel required to contact the brake drum.
The amount of travel increases as the brake shoe lining
wears.
When the brake pedal is released, the adjuster spring
retracts the brake adjuster arm which contacts the star
wheel. Note that adjustment only takes place when the
brake pedal is released while the vehicle is in motion.
If the brake shoes have worn far enough to permit the
brake adjuster arm to contact the next tooth of the star
wheel, the star wheel will be advanced by the tension
applied to the adjuster arm by the adjuster spring.
If the brake shoes have not worn enough to permit the
brake adjuster arm to contact the next tooth of the star
wheel, the brake adjuster arm will move on the flat of the
star wheel. The star wheel does not rotate and no
adjustment occurs.
Brake Lever
Brake Adjuster Arm
Star Wheel
Adjusting Screw
Adjuster Spring
Brake
Shoe
B
