OPERATOR'S MANUAL

Preventive Maintenance Air System
Medium Duty
(R05/09) Y53-6027 – 201 –
reduced braking capability). Other vehicles use a Bendix
AD-IS air dryer which eliminates the need for a wet tank
and check valves in the dry tanks.
NOTE: A small amount of oil in the system may be
normal and should not, by itself, be considered
reason to replace a desiccant cartridge; oil-stained
desiccant can function adequately.
Every 900 operating hours or 25,000 miles/40,000 km or 3
months, check for moisture in the air brake system by open-
ing reservoirs, drain cocks, or valves and checking for the
presence of water. A tablespoon of water in a reservoir would
point to the need for a desiccant cartridge change. However,
the following should be considered first:
• Air usage is exceptionally high/abnormal for a highway
vehicle. This may be due to accessory air demands or
some other unusual air requirement that doesn’t allow
the compressor to load/unload in a normal fashion or it
may be due to excessive leaks in the air system.
• When more than a 30-degree F. (17-degree C) range of
temperature occurs in one day, small amounts of water
can accumulate in the air brake system due to conden-
sation. Under these conditions, the presence of small
amounts of moisture is normal and should not be consid-
ered as an indication that the dryer is not performing
properly.
• An outside air source may have been used to charge the
air system, in which case this air did not pass through
the drying bed.
Air Intake System
Engine heat, vibration, and age combine to loosen air intake
connections and cause cracks in the tubing and elbows.
Leaks in the intake system allow abrasive dust to enter the
engine and quickly cause expensive damage. During your
daily walk-around inspection, carefully check all tubing,
elbows, clamps supports and fasteners for condition and
tightness.
• Under normal operating conditions, Peterbilt recom-
mends complete disassembly and cleaning of the air
intake system at each 25,000 mile (40,000 km). Under
severe operating conditions, the disassembly and clean-
ing should be more frequent. Replace any defective
parts. With the possible exception of mounting brackets,
do not repair defective parts.