Service manual

Group 59 Anti-Lock Brake System (Bendix) System Check
System Check
Function Checks
Note: Unless otherwise stated, there must be air pres-
sure in the brake system to perform the valve tests
described below.
Note: If any of the desired results for the tests below are
not met the valve should be repaired or replaced.
Traction Control Valve Function Check
PERSONAL INJURY HAZARD! Before working on a
vehicle, set the parking brakes, place the transmission
in neutral, and block the wheels. Failure to do so can
result in unexpected vehicle movement and can cause
serious personal injury or death.
PERSONAL INJURY HAZARD! Never disconnect an
air system component unless all system pressure has
been depleted. Failure to deplete system pressure be-
fore disconnecting hoses or components may result in
them separating violently and causing serious bodily
injury or death.
PERSONAL INJURY HAZARD! Exhaust gases con-
tain deadly poison. When testing a vehicle with the
engine running, conduct the test outdoors or use a
properly vented exhaust hose.
1 Drain air pressure from all vehicle reservoirs.
2 Install a tee at the traction control valve service port
and one of the delivery ports. Connect a test gauge
at each tee.
3 Connect the tractor service and emergency glad
hands to dummy connectors or to a trailer.
4 Start the vehicle and build system air pressure to
normal.
5 Make 5 full brake applications and check the test
gauge fittings for leaks. Tighten if necessary.
6 Activate the system park control and trailer supply
dash control valves for tractor/trailer operation.
7 Apply and release the brakes several times checking
for prompt application and release at each wheel.
8 If prompt application and complete release occurs at
some but not all wheels, test the ABS modulator
valve (M–22) between the traction control valve and
the brake actuator.
9 If a sluggish response or incomplete release is
noted at all wheels, inspect for system leakage or a
kinked or obstructed air line leading to or from the
traction control valve.
10 Apply and hold a full pressure brake application and
make sure that full pressure is delivered to the
brake chambers.
11 Set the dash mounted trailer air supply valve for
bobtail tractor operation (Yellow knob OUT).
12 Make a slow brake application up to 20 psi at the
traction control valve service port while observing
the pressure at the delivery port. Verify that the de-
livery port pressure rises to 5 to 10 psi (.34 to .69
bar).
13 Release the brakes.
14 Make a slow brake application up to 60 to 70 psi
(4.14 to 4.83 bar) at the traction control valve
service port while observing the pressure at the de-
livery port. Verify that the delivery port pressure
rises to 20 to 25 psi (1.38 to 1.72 bar).
Note: Delivery pressure should be approximately
one-third of service pressure.
15 Release the brakes.
16 Make a full brake application and verify both service
and delivery pressures register the same pressure.
17 If differential pressure test is not to be performed,
deplete the air from the system, remove the test
gauges, and restore the system to normal.
73