Specifications

Air System Preventive Maintenance
– 194 – Y53-6008A
Medium Duty (R05/09)
CAUTION: Do not use penetrating oil, brake
fluid, or wax-based oils in the air system. These
fluids may cause severe damage to air system
components.
• Maintain the air compressor to prevent excessive oil by-
pass. See the Medium Duty Maintenance Manual for
maintenance details.
• Replace worn seals in valves and air motors as they are
needed. Your Peterbilt Dealer carries rebuild kits for most
units.
Dual Air Gauge and Air Leaks
Your Medium Duty comes with a primary and secondary air
pressure guage. The gauge indicates the amount of air pres-
sure in pounds per square inch (psi).
See “Primary (Sec-
ondary) Air Pressure Gauge (Air Reservoir)” on page 41.
If the pressure in either or both systems is too low for normal
brake operation, i.e., either pointer falls below 60 psi (414
kPa), a warning light on the gauge will glow and the audible
alarm will sound. If the light and alarm do not turn off at start-
up, do not try to drive the vehicle until the problem is found
and fixed.
WARNING! Do not operate the vehicle if leakage
in the air system is detected. Conduct the follow-
ing procedure and contact an Authorized Ser-
vice Center (or any other properly equipped
service center) if a leak is detected. Failure to
check the brakes or follow these procedures
could cause a system failure, increasing the risk
of an injury accident.
Follow the procedure below to check the compressed air
system for leaks:
1. Periodically, or after maintenance or replacement of air
system components:
2. Build up air pressure in the system to the governor cut-
out point or until 120 psi (827 kPa) is reached.
3. Stop the engine and release the service brakes.
4. Without applying the brake pedal, observe the rate of air
pressure drop. This rate should not exceed 2.0 psi (14
kPa) per minute.
5. Start the engine and build up the air pressure again.
6. Stop the engine, and apply the brakes fully. Apply the
brake pedal and hold it down for five minutes. The pres-
sure drop should not exceed 3.0 psi (21 kPa) per minute.