JLG 534D-10 - Manual (Page 104)

Hydrostatic Drive Pump
6.6 534D-9, 534D-10 & 544D
6.6.4 Park Brake
Park brake wear can cause park brake failure and reduce
braking effectiveness on a slope.
With the park brake engaged, start the engine. Position
the 2WD/4WD switch in the 2WD position. With the rear
wheels aligned straight ahead, move the shift lever to the
forward position and run the engine at high idle. If the
brakes are working properly, the machine will not drive
through the brakes.
High backpressure in the actuation line can affect the
brake holding power. To determine whether the brake is
at fault, remove the brake actuation line and plug. Check
the park brake operation again. If the machine does not
move, the brake is working properly.
Backpressure should be less than 20 psi (1,38 bar) with
the oil at operating temperature. To check this pressure,
tee a low pressure gauge (1,000 psi - 69 bar), hose and
adapter in the brake actuation line. If it is higher, check for
proper operation of the park brake solenoid valve.
Disconnect the brake actuation line and tank return line at
the valve and plug them. There should be no oil flowing
from the open port on the back of the park brake solenoid
valve. The brake actuation line should not be kinked.
There should be no restriction back to the reservoir.
To check for friction disc wear, the axle must be
disassembled and reassembled according to the Carraro
Maintenance Manual. Detailed axle service instructions
are provided in the CA357248 Carraro Axle Service
Manual (JLG P/N 31200372).
6.6.5 Charge Pressure
To ensure proper park brake operation, charge pressure
needs to be at the proper specification. Since
temperature can affect results, make sure to test system
with hydraulic oil at a minimum of 100°F (38° C). Control
pressure is modified charge pressure. If charge pressure
is low, control pressure may be low and machine speed
reduced. Thus, drive performance is adversely affected
by low charge pressure.
Install a low pressure gauge (1,000 PSI - 69 bar), hose
and adapter on the charge pump test port. It is located
near the front inside of the hydraulic reservoir. Make sure
the gauge can be observed in the operators cab and
apply the park brake. Start the engine and run at low idle.
The gauge should read approximately 380 psi (26 bar). At
high idle the gauge should read a maximum of
480 psi (33 bar) and never less than 380 psi (26 bar).
Note: Throughout the test operation, charge pressure
should not drop below 380 psi (26 bar) and should move
toward 480 psi (33 bar) as RPM rises, regardless of how
many functions are being operated simultaneously.
The charge pump relief (1) adjusts as necessary. To
adjust the charge pump relief, loosen the locknut and turn
the adjusting screw clockwise to increase pressure; turn
counter clockwise to decrease pressure. Be sure to note
the amount of relief turns in either direction. When
finished, tighten the locknut and install a blue plastic cap.
To pinpoint the loss of charge pressure, start at the pump.
Make sure the machine is in 4WD when testing rear
motors. Remove the hose from the G port (charge pump
outlet port) (2) on the pump, install a low pressure gauge
(1,000 psi - 69 bar) on the fitting and plug the hose. Check
the charge pressure again and observe the gauge. If the
charge pressure comes back to specifications, the loss of
pressure is in one of the auxiliary valves. These valves
include the 2WD/4WD valve, traction lock valve, park
brake solenoid valve and the joystick. Isolate each of
these valves to check for loss of charge pressure.
MX1010
PARK BRAKE
ACTUATION
TANK RETURN
CHARGE
PRESSURE
PARK BRAKE
SOLENOID
VALVE
MX1060
T 2
P S
G
M A
M B
1
2