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 cannot drop. Failure to follow these steps
could result in serious personal injury or death.
42–01 Brake System Valves
Inspecting
1. Clean the valves exterior and inspect them for
corrosion and damage.
2. Inspect the air lines connected to the valves for
signs of wear or damage. Replace the lines as
needed.
3. Check the valves for leakage.
3.1 Apply the service brakes and hold them
on a full line pressure of at least 80 psi
(552 kPa).
3.2 Check the air line fittings for leaks; tighten
or replace the fittings as needed.
3.3 Coat the exhaust port and body of the
valves with soapy water, and check for
leakage. Leakage is excessive if it pro-
duces a 1-inch (25-mm) bubble within 5
seconds.
If a brake valve does not function as de-
scribed above, or if leakage is excessive,
replace it with a new or remanufactured
unit. Repeat the leakage checks before
placing the vehicle in service.
42–02 Air Dryer Checking
IMPORTANT: Review the warranty policy before
performing any intrusive maintenance proce-
dures. An extended warranty may be voided if
intrusive maintenance is performed during this
period.
Because no two vehicles operate under identical
conditions, maintenance and maintenance intervals
will vary. Experience is a valuable guide in determin-
ing the best maintenance interval for any one particu-
lar operation.
Every 12 months:
1. Check for moisture in the air brake system by
opening reservoir drain valves and checking for
presence of water. If moisture is present, the
desiccant cartridge may require replacement;
however, the following conditions can also cause
water accumulation and should be considered
before replacing the desiccant:
• An outside air source has been used to
charge the system. This air did not pass
through the drying bed.
• Air usage is exceptionally high and not nor-
mal. This may be due to high air system
leakage.
• In areas where more than a 30-degree
range of temperature occurs in one day,
small amounts of water can temporarily
accumulate in the air brake system due to
condensation. Under these conditions, the
presence of small amounts of moisture is
normal.
NOTE: A small amount of oil in the system is
normal and should not be considered as a rea-
son to replace the desiccant cartridge. Some oil
at the dryer exhaust is normal.
2. Visually check for physical damage, such as
chaffed or broken air and electrical lines and bro-
ken or missing parts.
3. Check the mounting bolts for tightness. See
Table 1 for torque values.
Torque Values
Vendor Size
Torque:
lbf·ft (N·m)
Bendix
Grade 5, 3/8–16 28 (38)
Grade 5, 5/8–11 135 (183)
Haldex 1/2–13 45 to 55 (61 to 75)
Table 1, Torque Values
4. Perform the operational and leakage tests listed
below.
Brakes 42
Recreational Vehicle Chassis Maintenance Manual, July 2018 42/1
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