SECTION 12: BRAKE AND AIR SYSTEM
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
23
27. AIR BRAKE
TROUBLESHOOTING
The following tests and check lists have been
designed to identify the cause(s) of a sluggish
performance and/or leaks in the system. These
tests require very little time to perform, and give
you a general idea of the system condition. Each
test is provided with a corresponding check list
which will guide you to the most common
causes of problems.
Before performing any test, check all air lines for
kinks or dents, and hoses for signs of wear,
drying out or overheating.
WARNING
When working on or around a brake system
and its related components, the following
precautions should be observed:
Always block vehicle wheels. Stop engine
when working under a vehicle. Keep hands
away from chamber push rods and slack
adjusters as they may apply when system
pressure drops.
Never connect or disconnect a hose or line
containing air pressure. It may whip as air
escapes. Never remove a component or pipe
plug unless you are sure all system pressure
has been depleted.
Never exceed recommended air pressure and
always wear safety glasses when working with
air pressure. Never look into air jets or direct
them at anyone.
Never attempt to disassemble a component
until you have read and understood the
recommended procedures. Some components
contain powerful springs and injury can result
if not properly disassembled. Use only proper
tools and observe all precautions pertaining to
the use of those tools.
Always clean connecting piping and/or fittings,
and coat pipe threads with Teflon pipe sealant
before installing any air brake system
component.
Pressure Build-Up / Low Pressure Warning /
Cutoff Point / Air Filter/Dryer Built-in
Governor Cutout
CONDITION: Vehicle leveled, parking brake
applied.
4. Completely drain wet, primary and
secondary air reservoirs only.
5. Start engine and run at fast idle. Low
pressure warning lights should be
"On"
.
6. Start checking pressure at 50 psi (344 kPa).
7. Low pressure warning lights and buzzer
should go off at or above 60 psi (415 kPa).
8. At 85 psi (586 kPa), run engine at max
recommended rpm, then check that build up
time to 100 psi (690 kPa) is 13 seconds or
less.
9. Air filter/dryer built-in governor cut-out. Cuts
out at the correct pressure of 140 psi.
10. Air filter/dryer built-in governor cut-in. Cuts in
around 122 psi.
For common corrections, refer to the following
check list:
High or Low Warning Cutoff Point
Perform a telltale light and gauge test.
Replace entire cluster if found defective.
High or Low Air Filter/Dryer Built-in Governor
Cutout Point
Perform a telltale light and gauge test.
Replace entire cluster if found defective.
OR
Repair or replace air filter/dryer as
necessary after checking that compressor
unloader mechanism operates correctly.
More than 13 seconds to build-up pressure
from 85 to 100 psi (585 - 690 kPa) at full
engine RPM
Perform a telltale light and gauge test.
Replace entire cluster if found defective.
Check compressor strainer or inlet line. If
restricted, clean or replace element or faulty
line.
Check compressor head or discharge line
for carbonization or restriction. Clean or
replace as necessary.
If discharge valves leak, pull head and
correct or replace cylinder head.
If drive is slipping, replace gear.
If inlet valves are stuck, open or leaking
severely, replace unloader kit, inlet valves
and/or seats as necessary.
If drain cock is found open, close it.
Listen for air leaks and repair.
Redo list to check all items repaired or
replaced.
Air Supply Reservoir Leakage
