Hydraulic System
8.4
3507, 3508, 3509, 3512, 3513, 4007, 4008, 4009, 4012, 4013
8.4
HYDRAULIC CIRCUITS
This section covers the hydraulic circuits and includes
listings for all hydraulic function pressures, where and
how to check those pressures.
Electrical and hydraulic functions are often related. Verify
that the electrical components of the circuit are
functioning properly whenever troubleshooting the
hydraulic circuit.
Always check the following before beginning to
troubleshoot a circuit that is not functioning correctly.
1. Check the hydraulic oil level in the reservoir. Oil level
should be at the middle of the sight glass with all
cylinders retracted.
2. Check hoses, tubes, fittings and other hydraulic
components for leaks, bends, kinks, interference,
etc.
3. Check for air in the hydraulic system. Erratic
machine performance and/or spongy cylinder
operation are signs of air in the hydraulic system.
4. If air in the hydraulic system is suspected, you will
hear air leakage when hydraulic fittings are loosened
and see air bubbles in the hydraulic fluid.
5. Loose fittings, faulty o-rings or seals, trapped oil,
leaks, system opened for service, etc., can cause air
in the system. Determine what is causing air to enter
the system and correct it. Bleed air from the system.
8.4.1
Checking Function Pressures
All hydraulic system function pressures can be checked
at one location. A digital pressure gauge is
recommended.
1. Start the machine and warm the hydraulic system to
operating temperature.
2. Shut off the machine and install a digital or a 345 bar
(5000 psi) gauge to the test port (
1
) located at the
top right corner of the main control valve.
3. Start the machine, run the engine at full throttle and
bottom the boom in function.
Note:
It is possible to see maximum system pressure by
activating and bottoming any of the hydraulic functions.
4. With the engine running at full throttle and the
hydraulic function bottomed, the gauge should read
250 bar (3625 psi) ± 5 bar (70 psi).
8.4.2
Adjusting Hydraulic Pressure
There is only one adjustment to set the main hydraulic
pressure.
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, lower the boom,
place the transmission control lever in (N)
NEUTRAL, engage the park brake and shut the
engine OFF.
2. Open the engine cover.
3. Remove the cap on the bottom relief on the pilot
valve at the main hydraulic pump located at the end
of the transmission.
4. Start the machine and loosen the jam nut on the
relief and using an allen wrench; turn the relief
clockwise to increase pressure or counter-clockwise
to decrease pressure. Set the pressure to 250 bar
(3625 psi) ± 5 bar (70 psi) at full throttle.
5. Tighten the jam nut and recheck the pressure at full
throttle. If the reading is within specification, shut the
machine off, install the safety cap and remove the
gauge from the test port.
6. If the proper pressure cannot be set, refer to Section
8.5, “Hydraulic Schematics,” or Section 9.5,
“Electrical System Schematics,” to help troubleshoot
the problem.
MZ1310
1
MZ1270
2
