J04031 Brake Circuit Check-Out Procedure J4-5
14. Release pedal, assure that each circuit's pres-
sure is zero.
· Record on data sheet.
15. To check pedal free play, refer to the procedure
"Additional Testing and Adjustment (With brake
pedal installed)" in this "Section J" of the service
manual.
NOTE: Free play is defined by the gap between the
setscrew (in the pedal structure) and the actuator
cap. There must be a gap to prevent brake drag.
16. Cycle brake lock several times to assure crisp
shift of solenoid valve and release of oil pres-
sure.
17. Apply brake lock and read brake pressures.
Front pressure should be zero and rear pres-
sure should be 1500 ± 100 psi (10343 ± 690
kPa).
· Record on data sheet.
Failure Modes Check-Out
18. Allow engine to run until low brake accumulator
pressure stabilizes at or above 3200 psi (22,064
kPa).
19. Shut engine down. Allow 90 seconds for the
steering accumulator to bleed completely down.
Disable steering pressure switch from the brake
warning circuit by unplugging the diode
between circuits 33 and 33F. (This is diode 22
on diode board 1) Turn key switch on. After two
minutes, record the low accumulator pressure
(LAP1 port). If LAP1 pressure is below 2600 psi
(17,927 kPa), then leakage in the system is
excessive and the source of the leakage needs
to be identified.
· Record on data sheet.
20. Crack the front brake accumulator bleed down
valve and observe LAP1 pressure. The Low
Brake Pressure lamp and buzzer must actuate
at 2300 ± 75 psi (15,859 ± 517 kPa).
· Record on data sheet.
21. Brake pressures should begin to rise (Auto
Apply) when LAP1 reaches 2000 ± 100 psi.
Close front brake accumulator bleed down
valve.
· Record on data sheet.
22. Start engine to recharge hydraulic system. Allow
engine to run until low brake accumulator pres-
sure stabilizes at or above 3200 psi (22,064
kPa).
23. Shut engine down. Allow the steering accumula-
tor to bleed completely down. Turn Key Switch
on. Crack the rear brake accumulator bleed
down valve and observe LAP1 pressure. Verify
that the Low Brake Pressure lamp and buzzer,
and Auto Apply set points are within a 100 psi
(690 kPa) of those recorded in step 20. Record
Auto Apply brake pressures. Close the rear
brake accumulator bleed down valve.
· Record on data sheet.
24. Enable the steering pressure switch by plugging
in the diode removed between circuits 33 and
33F.
25. Start the engine to recharge hydraulic system.
Allow engine to run until low brake accumulator
pressure stabilizes at or above 3200 psi (22,064
kPa).
26. Shut engine down. Do not allow steering accu-
mulator to bleed down. Make repeated slow,
complete brake applications with pedal until
auto apply comes on. Record the number of
brake applications prior to auto apply.
· Record on data sheet.
27. Bleed down both brake accumulators by fully
opening the manual bleed down valves on the
brake manifold.
28. Outside the brake cabinet, disconnect the hose
that supplies oil from the front brake accumula-
tor to the brake pedal in the cab for the front
brakes (port AF1) and plug the tube end at the
cabinet. Be sure to leave end of hose vented to
atmosphere.
29. Start engine and allow low brake accumulator
pressure (LAP1) to stabilize at 3200 psi (22064
kPa) before proceeding.
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