42–00 Safety Precautions
Safety Precautions in this section apply to all
procedures within this group.
DANGER
When working on the vehicle, shut down the en-
gine, set the parking brake, and chock the tires.
Before working under the vehicle, always place
jack stands under the frame rails to ensure the
vehicle can not drop. Failure to follow these steps
could result in serious personal injury or death.
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 vehicle Workshop Manual for
procedures.
IMPORTANT: For vehicles equipped with an oil-
coalescing air dryer desiccant cartridge, replace
the cartridge once a year, regardless of mileage.
42–02 Bendix Air Dryer
Desiccant Replacement
IMPORTANT: For vehicles equipped with an oil-
coalescing air dryer desiccant cartridge, replace
the cartridge once a year, regardless of mileage.
AD–9
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).
NOTE: The compressor discharge line may still
contain residual air pressure, open the line
slowly.
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 bolt that secures the upper mounting
bracket strap.
6.
Remove the two bolts and Nylok® nuts that se-
cure the air dryer to the lower mounting bracket.
Mark the position of the mounting bracket to the
end cover and mark the bolts to ease installation.
7.
Remove the upper mounting bracket strap fas-
teners, then remove the strap and the air dryer.
8.
Place the air dryer on a bench and remove the
remaining 6 bolts, 12 washers, 6 Nylok nuts, and
the air dryer housing. See
. Discard the
Nylok nuts. Remove the end-cover-to-housing
O-ring.
9.
Clamp the desiccant cartridge in a vise.
WARNING
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, resulting in property damage,
personal injury, or death.
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.
NOTICE
Dirt or obstructions in the O-ring grooves can
cause an O-ring failure that will result in an air
leak.
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.
Brakes
42
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