PREVOST X3-45 COMMUTER User Manual

SECTION 12: BRAKE AND AIR SYSTEM
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DOB 1300-1556 | X3-45 Commuter PA-1648 Maintenance Manual Section 12 revised Jan 2021
14. AIR SYSTEM TROUBLESHOOTING
Consult the following list to troubleshoot some of
the most common problems in the air system
and main causes. For air brakes
troubleshooting, refer to “Air Brakes
Troubleshooting” in this section. For more
troubleshooting information, refer to the
manufacturer's brochures, found on your
Technical Publications USB flash drive.
Air pressure does not rise to or does not
maintain a normal setting:
• Defective air gauge (registering incorrectly).
• Excessive leaking in air system.
• Tank drain cock open.
• Governor poorly adjusted or defective.
• Defective compressor.
• Worn compressor or excessive wear on
piston and/or ring.
Air pressure rises to normal setting too
slowly:
• Excessive leaking in air system.
• Clogged engine air cleaner.
• Faulty pressure sensor.
• Worn compressor or excessive wear on
piston and/or ring.
• Engine speed too low.
Air pressure rises above a normal setting:
• Defective air gauge (registering incorrectly).
• Faulty sensor.
• Restriction in line between governor and
compressor unloading mechanism.
• Air system governor defective.
Air pressure drops quickly when engine is
stopped:
• Leaks in compressor discharge valve.
• Leaks in air lines.
• Leaks in air system valves.
15. BRAKE OPERATION
The vehicle braking system uses both service
and parking air-operated brakes. The air system
is divided into two independent circuits to isolate
the front axle brakes and the rear axle brakes
(drive and tag), thus providing safe brake
operation in the event that one circuit of the
system fails. The primary circuit is connected to
the drive and tag axle brakes, while the
secondary circuit is connected to the front axle
brakes. The tag axle service brakes operate only
when the axle is in the normal driving (loaded)
position. The spring-type emergency/parking
brakes are mounted on the drive axle and will
apply automatically if primary system pressure
falls below 60 psi (413 kPa).
Brake application or release, which is speed up
by a pneumatic relay valve (R-14), will start with
the rear axles and be followed by the front axle,
thus providing uniform braking on a slippery
surface. The vehicle is also equipped with an
Anti-lock Brake System (ABS), detailed later in
this section.
The parking brake override system can cancel
the parking brakes, enabling the driver to move
the vehicle to a safe parking place. Operate this
system by pushing down and holding the control
knob located on the L.H. console (see
"Operator's Manual" for more details).
Brake and air system maintenance consists of
periodic inspections. Check all parts for damage
and brake adjustment (refer to subsequent
headings in this section for more details).
Ensure all fasteners are tight (refer to “Torque
Tables” for recommended tightening torques).

PREVOST X3-45 COMMUTER Specifications

General

Engine	Volvo D13
Transmission	Allison B500
Fuel Type	Diesel
Length	45 ft (13.7 m)
Width	102 in (2.6 m)
Horsepower	500 hp
GVWR	54, 000 lbs
Height	141 in