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BRAKE CARE AND ADJUSTMENT
T
he trailer brake system will perform safely and
efficiently only as long as it is properly maintained
and not abused. Trailer brakes should be inspected
frequently in connection with a Trailer Preventive
Maintenance (TPM) Program. Out-of-adjustment
b
rakes can cause increased stopping distance, shorter
brake component life, and a greater tendency for the
trailer to jackknife.
AIR SYSTEM AND BRAKE OPERATION
Proper operation of the brake systems requires a
firm seal between the air brake couplers. Inspect the
couplers for seal damage and cracked housings. Some
couplers are equipped with filters. These filters must
be cleaned at regular intervals to prevent malfunction
of the brake systems. Inspect the air hoses for cracking
and for frayed connections. Be sure air hoses are not
rubbing on any metal surface or each other. Replace
or repair damaged components.
Keep the air system clean. All air tanks should be
drained daily to remove moisture and other contami-
nants. See Freezing Weather Maintenance.
Some air valve manufacturers discourage the use of
air line antifreeze. Use may result in deterioration of
seals in these valves.
If you use Teflon tape or other thread sealers to seal
threaded connections in your air lines, be careful not
to allow pieces of the sealer to enter the air system.
It can clog passages into the valves and cause them
to malfunction.
Keep the air system tight. The air system cannot be
charged properly if there are leaks in reservoirs, lines,
hoses, or valves. Always check the tractor pressure
gauge for unusual drops or extended buildup times.
Run the tractor engine until the air brake system
pressure gauge shows at least 105 psi. Listen for air
leaks. With the engine off, check the gauge reading
with no brakes applied. The gauge reading loss
should not exceed three psi in one minute.
With the engine still off, apply the brakes fully for two
minutes. The gauge reading drop should not exceed
four psi in one minute.
With engine still off, slowly open drain cocks in the trail-
er’s air tanks and allow the pressure to drop gradually.
In a system employing spring brake control valves, the
spring brakes should function and apply the brakes.
In a system that does not employ spring brake control
valves, the relay emergency valve should function and
a
pply the brakes.
A schedule for periodic cleaning, inspection, adjustment
and lubrication of brake equipment should be estab-
lished by the operator, based on past experience and
severity of operation.
BRAKE SHOES
Brake shoe designs vary, depending on the type of
brake and brake manufacturer. Some brakes require
special tools. If you have problems removing brake
shoes, refer to the brake manufacturer’s manual.
BRAKE SHOE SPRINGS
Replace weak or unmated brake shoe springs whenever
they cause pulling or dragging brakes. The springs are
constantly expanding and contracting in the confined
hot area of the brake drums. Excessive heat during
expansion will cause them to weaken.
BRAKE LINERS
The certified Gross Axle Weight Rating (GAWR) in
many cases is determined by the friction level of the
brake liners. The friction level is determined by the
axle and vehicle manufacturer to provide the required
brake torque as prescribed by governmental regulations.
REFACING DRUMS
It is not a good practice to reface brake drums.
Refacing can weaken the drums, making them unable
to dissipate all the heat generated by brake applications,
and making them susceptible to distortion and heat
cracks.
If brake drums must be refaced on cam-type brakes,
when oversized linings are used, precautions regarding
cam travel should be checked to prevent sticking cams
or cam rollover. This problem often exists when the
linings become worn. It may be necessary to install
oversized rollers to prevent this problem.
WARNING Serious air leaks in the trailer’s
b
raking system are hazardous conditions that
require the trailer to be placed out of service
until they are properly corrected
NOTICE: When replacing liners, be sure to use
liners with the same friction level as those
removed from the trailer so that the GAWR is
not reduced.
8
WARNING Prior to performing maintenance
on any air brake system component, chock the
wheels. The system air pressure should be
exhausted by opening the reservoir drain cocks.