Manually Adjusting Brake Shoes; Electric Brakes - JLG T500J Service And Maintenance Manual

SECTION 3 - CHASSIS & TURNTABLE

Manually Adjusting Brake Shoes

The manually adjusted brakes should be adjusted in the fol-
lowing manner:
1. Jack up the trailer and secure it on adequate capacity
jack stands.
2. Be sure the wheel and brake drum rotate freely.
3. Remove the wheel and brake drum. Because of the spe-
cial stub axle arrangement, adjustment cannot be made
through the backing plate.
4. With a screwdriver or standard adjusting tool, rotate the
starwheel of the adjuster assembly to expand the brake
shoes. Adjust the brake shoes out until the pressure of
the linings against the drum produces a slight drag.
5. Remount the wheel and brake drum.
6. Repeat the above procedure on all brakes.
7. Lower the trailer to the ground.
3-2
3.3

ELECTRIC BRAKES

The electric brakes on a trailer are similar to the drum brakes
on an automobile. The basic difference is that the automotive
brakes are actuated by hydraulic pressure while electric trailer
brakes are actuated by an electromagnet. With all of the brake
components connected into the system, the brake will oper-
ate as follows:
1. Primary Shoe
2. Retractor Spring
3. Secondary Shoe
4. Hold Down Spring
Figure 3-1. Electric Brake Assembly
When the electrical current is fed into the system by the con-
troller, it flows through the electromagnets in the brakes. The
high capacity electromagnets are energized and are attracted
to the rotating armature surface of the drums, which moves
the actuating levers in the direction that the drums are turn-
ing.
The resulting force causes the actuating block at the shoe end
of the lever to push the primary shoe out against the inside
surface of the brake drum. The force generated by the primary
shoe acting through the adjuster assembly then moves the
secondary shoe out into contact with the brake drum.
Increasing the current flow to the electromagnet causes the
magnet to grip the armature surface of the brake drum more
firmly. This results in increasing the pressure against the shoes
and brake drums until the desired stop is accomplished.
5. Adjuster Assembly
6. Adjuster Spring
7. Magnet
8. Actuating Lever
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