Troubleshooting guide

59
www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)
TEST T WO
Air Leakage
Inspect for air leaks when working on a vehicle and
repair them promptly.
Park the vehicle on level ground and chock wheels.
Build system pressure to governor cut-out and allow
the pressure to stabilize for one minute.
Step 1: Observe the dash gauges for two additional
minutes without the service brakes applied.
Step 2: Apply the service brakes and allow the pressure
to stabilize. Continue holding for two minutes (you
may use a block of wood to hold the pedal in position.)
Observe the dash gauges. (Note: The Bendix
®
BVA-85
™
brake valve actuator enables pre-trip brake inspections
safely and easily with only one person. See page 46 for
more details.)
If you see a decrease of the dash air gauge readings of
more than:
• 4 psi for either service reservoir,
• 6 psi for a tractor/trailer combination,
• 8 psi for a tractor with two trailers,
during either two minute test, repair leaks and repeat
this test to confirm that the air leaks have been repaired.
NOTE: (A leak detector or soap solution will aid in
locating the leak.)
Air leaks can also be found in the charging system,
parking brakes, and/or other components (e.g. supply
lines and fittings, low pressure indicator(s), relay valves,
antilock modulators, dual brake valve, trailer control
valve, park control valve, tractor protection valve,
spring brake actuators, safety valve in supply reservoir,
governor, compressor discharge valves) - inspect and
repair as necessary.
Retest to check out all items repaired or
replaced.
Make all necessary repairs before proceeding to
Test Three.
TEST THREE
Brake chamber push rod travel
Check brake chamber push rod travel.
(Refer to chart for allowable tolerances)
Air Brake System Troubleshooting Tests (continued)
The angle formed between the brake chamber push
rod and the slack adjuster arm should be approximately
90° with an 80-90 psi brake application (as measured
with a test gauge either at the control gladhand or at
the brake valve primary delivery). If the angle between
the brake chamber push rod and the slack adjuster arm
is not approximately 90° then adjust slack adjuster arm
to obtain desired setting. If the brake chamber push
rod travel exceeds the allowable tolerance, then adjust
the adjuster arm to obtain the desired setting.
Retest to check out all items repaired or
replaced.
Make all necessary repairs before proceeding
to Test Four.
TEST FOUR
Parking Brake Application
Check with air system at full pressure, engine
idling between 600-900 RPM
1. Manually operate the park control valve and note
that parking brakes apply and release promptly as
the control valve button is pulled out and pushed
in.
For Tractor/Trailer Combinations:
(Do not use this test for a straight truck, buses, and
bobtail tractors:)
1. Manually operate the tractor protection control
valve (trailer supply valve usually red octagonal
button). Note that the trailer brakes apply and
release promptly as the control button is pulled out
and pushed in.
Brake Maximum Stroke
Chamber Before
Size Readjustment
12 . . . . . . . . . . . . 1 1/8"
16 . . . . . . . . . . . . 1 3/4"
20 . . . . . . . . . . . . 1 3/4"
24 . . . . . . . . . . . . 1 3/4"
30 . . . . . . . . . . . . . 2"