JLG T500J, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121200 3-3
Brake Controller
A tow vehicle brake controller is required. These controllers
have gain control to vary the amount of current to the brakes,
and a level control which sets the controller's inertia sensor to
sense deceleration. The level adjustment also can be used to
vary when the trailer braking is felt. The gain or output control
adjustment usually controls the maximum amount of amper-
age available to the brakes. This can be adjusted for varying
trailer loads.
The electric brakes that operate in conjunction with the tow
vehicle brakes must be “synchronized” so that braking is prop-
erly distributed to the tow vehicle brakes and the trailer
brakes. For proper operation and synchronization, read and
follow the axle/brake and the brake controller manufacturers’
instructions
Brake Cleaning and Inspection
Your trailer brakes must be inspected and serviced at yearly or
12,000 miles intervals or more often as use and performance
requires. Magnets and shoes must be changed when they
become worn or scored thereby preventing adequate vehicle
braking. Clean the backing plate, electromagnet, and brake
shoes. Make certain that all the parts removed are replaced in
the same brake and drum assembly. Inspect the magnet arm
for any loose or worn parts. Check shoe retractor springs, hold
down springs, and adjuster springs for stretch or deformation
and replace if required.
Shoes and Linings
A simple visual inspection of your brake linings will tell if they
are usable. Replacement is necessary if the lining is worn (to
within 1/16” or less), contaminated with grease or oil, or
abnormally scored or gouged. It is important to replace both
shoes on each brake and both brakes of the same axle. This is
necessary to retain the “balance” of your brakes.
3.4 HYDRAULIC (SURGE) BRAKES
In the hydraulic brake system, hydraulic fluid from the master
cylinder is used to actuate the hydraulic wheel cylinder, which,
in turn, applies force against the brake shoes and drum. The
main differences between automotive hydraulic brakes and
hydraulic trailer brakes are the actuation systems that transfer
the braking signal from the tow vehicle to the brake. A surge
tongue actuator is required for a trailer with hydraulic brakes.
The hydraulic brake uses a single acting cylinder. Upon actua-
tion, the primary shoe is pressed against the brake drum,
which causes the shoe to move in the direction of rotation.
This movement in turn actuates the secondary shoe through
the adjuster link assembly. Braking in reverse is significantly
less effective than in the forward direction.
The hydraulic braking system must be inspected at least as
often as the brakes on the tow vehicle, but no less than once
per year. This inspection includes an assessment of the condi-
tion and proper operation of the wheel cylinders, brake shoes,
brake drums and hubs.
Check the fluid level in the master cylinder reservoir at least
every three months. If you tow your trailer an average of 1,000
miles per month in a hot and dry environment, you must
check the brake fluid level once a month. The brake fluid reser-
voir is located on the tongue of the trailer. Fill with DOT 3 or 4
brake fluid.
1. Anchor Post
2. Wheel Cylinder
3. Hold Down Spring
4. Primary Shoe
5. Adjuster Assembly
6. Adjuster Spring
7. Secondary Shoe
8. Backing Plate
9. Retractor Spring
Figure 3-2. Hydraulic Brake Assembly