TM 9-4940-549-14&P
TRAILER CHASSIS AND COMPONENTS
GENERAL. The trailer chassis is specially made for this shop set.
It con-
sists Of a 36,000-lb. capacity, dual-tandem axle assembly, air over hy-
draulic braking system, and a manually operated mechanical retracting
landing gear assembly. The trailer is electrically wired to the front
and rear intervehicular receptacles to transmit 24-volt DC current from
the towing vehicle to the taillights and clearance lights on the shop set
body.
WHEELS AND BRAKE SYSTEM.
General. The trailer rides on two sets of dual wheels and is stopped
by air over hydraulic brakes actuated by air supplied from the towing
vehicle or cab. The air reservoir stores air received from the towing
vehicle for operating the air-hydraulic cylinders. During normal oper-
ation, the air pressure in the air reservoir will be the same as the
towing vehicle reservoir. The braking system uses a dual-purpose valve
called "emergency relay valve". It directs air pressure to the air-hy-
draulic cylinders when the brakes are applied, and will automatically set
the trailer brakes if the trailer becomes separated from the towing vehi-
cle.
TESTING AIRBRAKE SYSTEM FOR LEAKS.
Dry Test. Connect the trailer brake system to the towing vehicle
a.
brake system. Make sure the towing vehicles brake system is in
good condition. Charge both systems to 100 psi with the air com-
pressor and turn off the engine. Without applying the brakes, the
drop in air pressure should not exceed three pounds per minute.
Apply the brakes fully and observe the drop in pressure. The rate
should not exceed four pounds per minute. If air leakage is exces-
sive, isolate the defective component by following the test procedure
in b, below.
Wet Test. Apply a liquid soap solution to the brake system compo-
b.
nents and connections with a brush. Observe for signs of leakage
when the brakes are fully applied and when they are released. To
inspect the emergency-relay valve for leakage in the emergency posi-
tion, shut off the vehicles's emergency line and disconnect it from
the trailer. Inspect for leakage at the emergency relay valve.
NOTE
If leaks are at connection points,
tighten the connections. Repair or
replace defective components. Re-
port uncorrected deficiencies to
direct support maintenance.
