JLG sky trak mmv Service Manual page 380

Hydraulic System
1
b. Four-Wheel Steering
When the steer select switch (1) is in the four-
wheel steer (down) position (2), the front wheels
(3) will steer in the direction the steering wheel is
MT3880
turned and the rear wheels (4) will steer in the op-
posite direction.
1. Four-Wheel Steering Left Turn (See page 9.60)
With the steer select switch (1) in the four-wheel steer
(down) position (2), one of the steer select valve sole-
noids is energized. The power steering unit control valve
spool is shifted so that the system pressure from the ac-
cumulator charge valve is applied to the intake side of the
power steering unit metering section.
A specific amount of hydraulic oil is exhausted from the
metering section and routed back to the power steering
control valve section, internal to the power steering unit,
where it is channeled to the left rod end of the rear steer-
ing cylinder.
Oil from the right rod end of the rear steering cylinder
flows through the steer select valve to the left rod end of
the front steering cylinder. Oil from the right rod end of the
front steering cylinder flows to the power steering control
valve, then to the return filter in the reservoir.
9.82
3
2
1
4
2. Four-Wheel Steering Right Turn (See page 9.62)
With the steer select switch (1) in the four-wheel steer
(down) position (2), one of the steer select valve sole-
noids is energized. The power steering unit control valve
spool is shifted so that the system pressure from the ac-
cumulator charge valve is applied to the intake side of the
power steering unit metering section.
A specific amount of hydraulic oil is exhausted from the
metering section and routed back to the power steering
control valve, internal to the power steering unit, where it
is channeled to the right rod end of the front steering
cylinder.
Oil from the left rod end of the front steering cylinder flows
through the steer select valve to the right rod end of the
rear steering cylinder. Oil from the left rod end of the rear
steering cylinder flows through the steer select valve and
back to the power steering control valve, then to the re-
turn filter in the reservoir.
MM1810
Model MMV Rev. 12/04