25
MAINTENANCE
4. Tighten the inner spindle nut while rotating the
wheel or hub both directions until a slight bind is felt.
5. Loosen the nut 1/4 turn. The wheel or hub must
rotate freely.
6. Install the inner nut lock and place the outer lock-
washer on the spindle.
7. Tighten the outer nut.
8. The end play must be .001 in. (.0254 mm) to .010
in. (.254 mm).
9. Lock the outer spindle nut in place by bending
the tangs or edge of the lockwasher over one flat on
the outer nut.
10. Install the hub cap gasket and hub cap. Fill the
hub to the “Full” line on the hub cap window (see
Figure 7
).
11. Adjust the brakes.
Air Systems and Brakes
Air Systems and Brakes - General
This section contains a description of the operation
of the trailer brake air supply system.
Also included in this section are test instructions,
disassembly and assembly procedures and a trouble-
shooting guide.
Air System Tests
A series of tests must be run daily before operating
trailers with air brakes.
1. Connect the air lines, turn on the air, and pressur-
ize the system. The system must hold 100 PSI (7 Bar)
pressure minimum.
2. Apply the brakes. Inspect the brake action on all
the wheels for proper application.
3. Release the brakes. The brakes must release
promptly. Air pressure must discharge quickly from the
relay emergency valve.
4. Disconnect the emergency line from the trailer.
The trailer brakes must automatically apply.
5. Connect the emergency line. The brakes must
release.
Air Reservoir
Drain condensation from the reservoir while the res-
ervoir is pressurized. Listen for leaks after closing the
drain valve. The drain valve is located on the underside
of the reservoir.
Air Hoses and Tubing
Air hoses and tubing must be checked for chafing,
bends, and kinking. Replace faulty parts.
Brake Relay Emergency Valve
The air system tests may disclose a malfunction of the
relay emergency valve. Repair or replace faulty units.
Contact an authorized representative of the original
equipment manufacturer for relay valve servicing.
Air Brake Chambers
The air system tests should disclose any malfunction-
ing brake chambers. Repair or replace faulty units. The
diaphragm and any worn parts must be replaced. When
replacing the diaphragm or the spring, replace the cor-
responding parts for the other chamber on the same axle,
to aid in even brake application and release. Examine
the yoke pin for wear and replace it if necessary.
Brake Air Supply System Description
(see
Figure 20
)
The trailer relies on the tractor for its air supply. A
description of the system operation follows:
1. When the service and emergency lines are con-
nected to the towing vehicle, the reservoir is charged
to approximately the same pressure as is present in the
tractor reservoir. The relay emergency valve will keep
the trailer brakes applied until the emergency line pres-
sure reaches 60 PSI (4.14 Bar). The brakes will then
be released.
2. When the towing vehicle and the trailer are travel-
ing over the road, the brakes are released and the emer-
gency line and reservoir are charged to full pressure.
3. When the service brakes are applied in the towing
vehicle, the pressure is increased in the service line. This
fills the brake chambers with the same pressure as the
service line, and applies the trailer brakes.
4. Releasing the service brakes will cause the pres-
sure in the service line to decrease, causing the relay
emergency valve to exhaust the pressure from the brake
chambers.
5. The trailer brakes can also be applied independent-
ly from the tractor brakes by actuating a hand controller.
This supplies air pressure to the service line.
6. The brakes will also apply if the pressure in the
emergency line is reduced to about 30 PSI (2.07 Bar).
A gradual decrease in the emergency line pressure will
cause a gradual increase in the pressure to the brake
chambers.
7. A sudden release of pressure in the emergency line
will cause a full release of reservoir pressure into the
brake chambers, resulting in full brake application.
