AIR BRAKES - GENERAL INFORMATION
PRELIMINARY CHECKS
NOTE - Before conducting the Pressure Balance,
Pressure Build-up Rate, and the Torque Balance Tests,
make the following checks of the air brake system on the
tractor-trailer combination. These checks are intended
to detect and correct conditions which otherwise could
produce misleading or Inconclusive test results.
1.
Check the adjustment of all brakes on both the
tractor and trailer(s). Adjust the brakes as
required.
2.
Visually check the slack adjuster movement (if
applicable) to determine that all brakes are
actuating and releasing freely. If not, inspect
and lubricate the suspect brakes thoroughly. DO
NOT allow any lubricant on the linings, drums, or
rotors.
3.
Check the air brake system to be sure that it is
free of significant air leaks. Air leakage should
not exceed the following values with an air
system pressure of 655 kPa (95 psi) or more
and the brake pedal released:
13.8 kPa (2 psi) per minute, on tractor only.
20.7 kPa (3 psi) per minute, on tractor with
trailer combination.
34.5 kPa (5 psi) per minute, on tractor with
two trailer combination.
Repair any leakage points if these values are
exceeded.
4.
Drain the reservoirs of any moisture and con-
tamination.
5.
Visually inspect for damage or kinked lines and
replace any lines found to be defective.
6.
Inspect combination units for loose fifth wheel
and kingpin condition. A loose fifth wheel to
kingpin fit can exaggerate an unbalanced brake
condition and therefore must be adequately
tightened.
Any deficiencies found in the above areas may be con-
tributing factors in the brake complaints. These should
be considered in the overall analysis of the brake
system.
TEST EQUIPMENT
The test equipment described below and illustrated in
Figure 23, with the exception of the Brake Timing Unit, is
required in conducting the pressure balance, pressure
build-up rate, and torque balance tests. DOUBLE
GLADHAND ASSEMBLY
Figure 23Air Brake Test Equipment
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