J2-6 Brake Circuit J02037
BRAKE LOCK CIRCUIT
The primary function of the brake lock is to provide a
means for the operator to hold the vehicle while at
the shovel or dump. The brake lock only applies the
rear service brakes. It may also provide a second
means to stop the truck in the event the primary
means (treadle valve) malfunctions.
By turning on the dash mounted toggle switch, a
solenoid valve (15, Figure 2-1) and pressure reduc-
ing valve (PR2, 14) will apply unmodulated pressure
oil at 10343 ± 517 kPa (1500 ± 75 psi) to fully actuate
the rear brakes. A shuttle valve (13) in the rear brake
line provides the independence from the brake trea-
dle valve for brake application.
WARNING CIRCUIT
The brake warning circuit is equipped with a low
brake pressure warning light (on the overhead panel)
and an audible alarm (in the cab) to alert the operator
of low brake pressures. Several electrical sensors, a
relay and delay timer are used to detect brake sys-
tem problems.
• Pressure Sensor, system supply pressure
Located below the bleed down manifold on a tee
fitting is the low steering pressure switch. When
system supply pressure drops below 15860 kPa
(2300 psi), the low steering pressure light, low
brake pressure light and buzzer will turn on.
• Pressure Sensor, low accumulator pressure
(22)
Located on the brake manifold. When the
accumulator with the lower hydraulic pressure
falls below 15860 kPa (2300 psi), the low brake
pressure light and buzzer will turn on.
• Brake Lock Degradation Switch (9, Figure 2-1)
Located on the junction block (10) in the brake
cabinet. When the brake lock switch is turned
ON, the brake warning light relay is energized.
This switches the electrical connection to the low
brake lock pressure switch circuit. If the brake
lock apply pressure is less than 6900 kPa (1000
psi), a path to ground will be completed and the
low brake pressure light and buzzer will turn on.
NOTE: This switch (9) and pressure sensor (27) can
be located in either port, and the operation will be the
same. If pressure sensor (27) is in the location
shown in Figure 3-1, there may be more clearance
for the wires around other components.
• Brake Warning Relay (25)
Located in the brake cabinet. When the brake
lock switch is turned ON, the brake warning light
relay is energized. This switches the electrical
connection to include the low brake lock pressure
switch. When the brake lock switch is turned
OFF, the relay is de-energized and switches the
connection away from the low brake lock apply
pressure switch.
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