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
engine or motor, 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 cannot drop. Failure to follow these
steps could result in serious personal injury or
death.
42–01 Air Brake System Valve
Inspection
IMPORTANT: There is no scheduled (Bendix) air
valve maintenance that requires disassembly of
the valve within the warranty period. If the valve
does not function within the warranty period, do
not disassemble the part as this will void the
warranty.
See the following maintenance operations for
information about Bendix air valve maintenance.
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
secure 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
fasteners, 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
Fig. 1. 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
desiccant cartridge.
NOTE: A substantial torque, up to 50 lbf·ft (68
N·m), may be necessary to remove the
desiccant 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.
12. Lubricate the O-rings with silicone or lithium
grease and install them in the end cover.
Brakes 42
Business Class M2 Plus Maintenance Manual, 02/10/2023 42/1
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