TM 5-3655-210-12
b. Relay-Emergency
Valve.
trailer reservoir from escaping through the broken or
The
relay
disconnected line, and at the same time permits air
emergency valve relays the braking action from the
pressure in the trailer reservoir to flow to the trailer
truck or tractor and provides an automatic application of
brake chambers, applying the brakes.
the trailer brakes in the event the trailer breaks away
c. Parking. Disconnecting the trailer from the
from the truck or tractor.
c. Actuator. Actuators transform the energy of
tractor will automatically apply the brakes on the trailer.
Do not, however, leave the trailer parked depending on
compressed air into the mechanical force necessary to
the air brakes to hold it if there is any danger of it
apply the brakes. One actuator is used to operate the
moving should the air pressure leak off and, the ,brakes
brakes on each wheel.
d. Slack Adjusters. Slack adjusters, on the brake
release. In such cases, the wheels must be blocked to
prevent the trailer moving. If the brakes on a trailer
camshaft, provide a quick and easy method of adjusting
have been applied automatically and it is necessary to
the brakes to compensate for lining wear. One slack
release them without reconnecting the trailer to the truck
adjuster is used for the brakes on each wheel.
e. Reservoir. The reservoir stores the compressed
or tractor, open the trailer reservoir drain cock. This will
release the air pressure in the trailer brake system and
air until it is needed for brake operation.
f. Drain Cock. A drain cock at the bottom of the
the brakes will release.
reservoir permits the draining of condensation, which
4-71. Brake Adjustment
normally collects there.
Refer to figure 4-73 and adjust each slack adjuster
so the wheel brake just drags slightly, and the angle
the ends of the service line and the emergency line
between the push rod and slack adjuster arm is greater
provide a means of attaching hose connections from the
than 90 when brakes are applied, as shown in figure 4-
truck or tractor air brake system.
h Tubing and Tubing Fittings. Tubing and tubing
74.
fittings connect the air brake devices in the air brake
4-72. Wheel Brake Replacement
system.
i. Hose Assemblies. Hose assemblies are used
a. Jack up trailer and remove wheel and brake
drum.
where it is necessary to' have a flexible air line between
b. Refer to figure 4-75 and remove items in the
two points of the trailer which change their position in
following order:
relation to each other.
(1) Brake spring.
4-70. Operation
(2) Anchor pin retaining rings and spring pins.
a. Normal. The trailer reservoir is kept charged by
(3) Anchor pins and brake shoes.
(4) Cam roller retaining rings and the rollers.
compressed air flowing from the tractor reservoir
c. Reverse steps a and b above to complete
through the emergency line and through the relay-
replacement and adjust brakes as follows: -Refer to
emergency valve to the reservoir on the trailer. When
figure 4-73 and adjust each slack-adjuster so the wheel
the brakes are applied compressed air flows from the
brake just drags slightly, and the angle between the
brake valve on the tractor through the service line to the
push rod and slack adjuster arm is greater than 90
relay-emergency valve. The relay-emergency' valve
when brakes are applied, as shown in figure 4-74.
then operates to permit air pressure to flow from the
trailer reservoir to the trailer brake chambers, applying
4-73. Slack Adjuster Replacement
the brakes. If the brakes on the tractor are released the
a. Refer to figure 4-73 and disconnect push rod
relay emergency valve permits air pressure in the trailer
clevis from slack adjuster.
brake chambers to escape to atmosphere. The relay
b. Remove retaining ring from camshaft., splined
emergency valve always reacts to keep the same air
end and take off slack adjuster.
pressure in the trailer brake chambers as the brake
c. Reverse a and b above to install replacement
valve is delivering through the service line. Thus the air
slack adjuster, then adjust brakes as follows: Refer to
pressure in the trailer brake chambers and the
figure 4-73 and adjust each slack adjuster so the wheel
effectiveness of the trailer brakes are controlled by the
brake just drags slightly, and the angle between the
driver operating the brake valve on the towing vehicle.
b. Emergency. In the event the trailer breaks away
push rod and slack adjuster arm is greater than 900
when brakes are applied as shown in figure 4-74.
from the towing vehicle breaking the emergency line, or
if the emergency line is disconnected, the relay-
emergency valve operates to prevent air pressure in the
4-80
