JLG 67SL Service Manual - Manual (Page 33)

SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3121322 – JLG Lift – 3-1
SECTION 3. CHASSIS, PLATFORM & SCISSOR ARMS
3.1 OPERATING CHARACTERISTICS
NOTICE
ANYTIME SERVICING OF ELECTRICAL OR HYDRAULIC COMPO-
NENTS IS REQUIRED, DISCONNECT BATTERY VIA THE DISCON-
NECT SWITCH ON THE GROUND CONTROL PANEL AND SHUT
VALVE LEVERS AT THE BASE OF THE HYDRAULIC TANK TO
STOP FLOW OF HYDRAULIC FLUID.
Leveling Jacks
The machine is equipped with auto leveling jacks. The
automatic self leveling system is controlled by 4 double
acting cylinders mounted at each corner of the machine
chassis. These cylinders incorporate pilot operated hold-
ing valves on the piston side. The cracking pressure of
these valves is 15 psi (1 bar) for the rear and 116 psi (8
bar) for the front.
1. Activate the leveling jack switch located on the
ground control console.
2. Extend the jacks by moving the joystick on the plat-
form control box forward.
NOTE: The jacks deploy at idle engine speed. Once all four
jacks make contact with the ground the system will
go from set mode into level mode. Once level,
engine rpm’s will increase and lift is allowed.
3. The tilt indicator LED’s on the Main Terminal Box will
go out once the machine is level.
NOTE: There are limit switches mounted at each jack cyli-
inder. These sense when the jack makes ground
contract and enable the lift function. All four switches
must have contact (lift indicator LED on the platform
will light) to enable lift. When elevated, if a contact
signal is lost (jack loses ground contact, wire cut,
etc.), the lift function is stopped and only lowering is
permitted.
The jacks are operational (extend or retract) if the
machine is in the stowed position. The minimum
height limit switch must sense the machine is
stowed. A failure of the limit switch will prevent the
jacks from being activated.
NOTE: Refer to Section 5.3, Nivolux - Automatic Self-Level-
ing System for detailed information regarding the
automatic leveling system.
3.2 WHEEL ASSEMBLY
Drive System
Wheel drive is achieved by orbital type (100cc/rev)
hydraulic motors driving a wheel type gearbox (29.8:1
reduction) through a spring-applied brake.
The brake is released by actuating a 3 way solenoid valve.
This valve provides hydraulic power from the pump
directly to the brakes. The brake can be reset by deacti-
vating the valve and restricting flow to the tank through an
orifice to smooth out hard stops. Drive is controlled by a
proportional solenoid valve section within the main control
valve (see Figure 4-33.).
Flow to the drive motors passes through a series /parallel
solenoid. When all 3 solenoids are in the passive (non-
energised) mode, flow is split by 3 flow dividers:
• Front/Rear
• Rear - Left/Right
• Front - Left/Right
When the solenoids are activated, all ports on the rear
hydraulic motors are connnected so that they free the
wheel. The front motors are connected in series (output of
one motor to the input of the other) to enable fast drive
low torque mode.