JLG 80SL Service Manual - Manual (Page 37)

SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3121325 – JLG Lift – 3-1
SECTION 3. CHASSIS, PLATFORM & SCISSOR ARMS
3.1 OPERATING CHARACTERISTICS
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 and116 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 resets by deactivating the valve and
restricting flow to the tank through an orifice to smooth out
hard stops.
Drive is controlled by 2 proportional solenoid valve sec-
tions within the main control valve. Flow to the drive
motors passes through a 4-section solenoid drive valve
manifold 2 for differential lock and 2 for fast drive.
There are three modes for drive selected by the drive
speed select switch on the platform control console:
1. Normal Drive - 4 wheel drive
2. Differential Lock - 4 wheel drive with flow dividers
3. Fast Drive - 2 wheel drive
Normal Drive:
Flow passes from section 9 to the front drive section of the
drive valve (ports A1 & B1) and from section 2 to the rear
section of the drive valve ports (A2 & B2).
All 4 solenoids on the drive valve are in the passive (non-
energized) mode. Flow from A/B1 passes directly to the
front drive motor ports (C/D1 & C/D2) and from A/B2 to
the rear drive motors (C/D3 & C/D4).
Differential Lock:
As in normal drive, flow passes from section 9 to the front
drive section of the drive valve (ports A1 & B1) and from
section 2 to the rear section of the drive valve ports (A2 &
B2).
The 2 differential lock solenoids are energized which
directs the flow through 2 flow dividers in the drive valve.
These split the flow to the left and right front motors (1 &
2) and to the rear motors (3 & 4).
Fast Drive:
Valve section 2 is not used in fast drive. Flow from section
9 passes to the front section of the drive valve. The 2 fast
drive solenoids are energized which connect the ports of
the rear drive motors (C3 to D3) and (C4 to D4). This
allows the rear drive motors to free wheel.