42–01 Air Brake System Valve
Inspection
NOTE: There is no scheduled air valve mainte-
nance on vehicles equipped with Bendix air
valves and a Bendix air dryer if the air dryer
desiccant is replaced at 350,000 miles (563 000
km). If the desiccant is not changed at 350,000
miles (563 000 km), or if the vehicle is equipped
with another air dryer, maintenance will have to
be performed to the air brake valves. See
Group 42 of the
Century Class Trucks Work-
shop Manual
for procedures.
42–02 Bendix AD–9 Air Dryer
Desiccant Replacement
1. Park the vehicle on a level surface. Apply the
parking brakes and chock the tires.
2. Completely drain all air reservoirs. Air pressure
gauges should read 0 psi (0 kPa).
CAUTION
The compressor discharge line may still contain
residual air pressure.
3. Identify, tag, and disconnect the three air lines
from the end cover.
4. Disconnect the harness connector from the
heater and thermostat assembly.
5. Loosen the capscrew securing the upper mount-
ing bracket strap.
6. Remove the two capscrews that secure the air
dryer to the lower mounting bracket. Mark the
position of the mounting bracket to the end
cover, and mark the capscrews to ease installa-
tion.
7. Remove the upper mounting bracket strap cap-
screw, and remove the air dryer from the vehicle.
8. Place the air dryer on a bench and remove the
remaining 6 capscrews, 12 washers, 6
Nylok
®
nuts, and the air dryer housing. See
Fig. 1. Discard the Nylok nuts. Remove the end-
cover-to-housing O-ring.
9. Clamp the desiccant cartridge in a vise.
CAUTION
Clamping the end cover or housing in a vise could
seriously compromise the air dryer’s ability to
hold air pressure, which could cause a failure in
the brake system.
10. Twist the end cover counterclockwise to release
the cartridge from the end cover. Rotate the end
cover until it completely separates from the des-
iccant cartridge.
NOTE: A substantial torque, up to 50 lbf·ft (68
N·m), may be necessary to remove the desic-
cant cartridge.
11. Inspect the condition of the O-ring seals. If they
are cracked, crimped, or otherwise damaged,
replace them to ensure an airtight seal. Clean
the O-ring grooves of any dirt or obstruction.
CAUTION
Dirt or obstructions in the O-ring grooves can
cause an O-ring failure that will result in an air
leak.
12. Lubricate the O-rings with silicone or lithium
grease and install them in the end cover.
13. Install the desiccant cartridge on the end cover.
Turn the cartridge clockwise until the desiccant
cartridge makes contact with the end cover.
14. Place the desiccant cartridge in a vise, and turn
the end cover clockwise an additional 180 to 225
degrees to fully tighten the desiccant cartridge to
the end cover.
NOTE: Desiccant cartridge torque should not
exceed 50 lbf·ft (68 N·m).
15. Place the housing over the desiccant cartridge
and align the mounting holes with the end cover.
IMPORTANT: Replace, do not reuse the Nylok
nuts on the air dryer cover.
16. Install the 6 capscrews, 12 washers, and 6 new
Nylok nuts. Torque the capscrews in a star pat-
tern (see Fig. 2) 270 to 385 lbf·in (3060 to 4340
N·cm)
17. Install the air dryer on the lower mounting
bracket. Install the two previously marked cap-
screws, four washers, and two new Nylok nuts.
Torque the two remaining capscrews 270 to 385
Brakes 42
Century Class Trucks Maintenance Manual, April 2005 42/1
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