JLG 340AJ Service Manual - Manual (Page 70)

SECTION 3 - CHASSIS & TURNTABLE
3-30 – JLG Lift – 3121259
3.8 OSCILLATING AXLE SYSTEM
The oscillating front axle is attached to the frame by a pivot
pin, which allows all four wheels to remain on the ground
when traveling on rough terrain. The oscillating axle incorpo-
rates two lockout cylinders connected between the frame and
the axle. The lockout cylinders permit axle oscillation when
the main boom is in Transport Position (see Section 4), and
when the boom is oriented between the rear tires as described
under Drive Orientation System. In this system, both of these
boom positions (swing and main boom elevation) are sensed
by two switches. One switch in each position is normally
closed and positively opens in the unsafe state (these are the
same switches described in the Transport Position Sensing
System (see Section 4) and in the Drive Orientation System.
The other switch for each position is normally open and closes
in the safe state.
The lockout cylinders will lock and hold the axle when the
boom is in a position as described above (Main boom above
horizontal or swung beyond the rear tires). The cylinders
unlock when pilot pressure is applied to the holding valves
mounted on the cylinders and lock when pilot pressure is
removed.
Pilot pressure is supplied via Drive Pump charge pressure.
When the control system detects that the Main Boom is below
horizontal and swung between the rear tires, two control
valves are actuated to supply charge pressure to the lock-out
cylinder holding valves. This allows the cylinders to unlock
which allows the axle to float. The first valve is normally closed
and opens when actuated to allow flow to the lock-out cylin-
der circuit. The second valve (located between the first valve
and the lock-out cylinders) is normally open to tank. This
valve closes when actuated to block the tank path and force
the flow to the lock-out cylinders. If either of these valves is in
its normal state, the axle will be locked.
Oscillating Axle Bleeding Procedure
1. Start the engine.
2. Position the turntable to the normal stowed position.
3. Position a small container suitable for containing
hydraulic oil in front of the lockout cylinder bleeder.
4. Using a 3/8" wrench, loosen the bleeder by slowly turn-
ing counterclockwise.
5. Bleed approximately 2 cups (0.2 L) of fluid from the
bleeder in the cylinder. Tighten the bleeder while the
machine is running.
6. Locate the bleeder on the opposite lockout cylinder and
repeat steps 3 thru 5.
SWITCH #1 LOCATED CLOSET TO BEARING,
ARM WILL BE IN THE VOID WHEN THE
MACHINE IS IN THE STOWED POSITION
SWITCH #2 LOCATED
FARTHEST FROM BEARING,
ARM WILL BE ON THE RAMP
WHEN THE MACHINE IS IN
THE STOWED POSITION
Figure 3-28. Axle Oscillation Switches