JLG 1250AJP Service Manual - Manual (Page 62)

SECTION 3 - 1CHASSIS & TURNTABLE
3-14 – JLG Lift – 3121171
3.10 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 also incorporates two lockout cylinders connected
between the frame and the axle. The lockout cylinders
permit axle oscillation when the boom is in the transport
position (see Section 4.2, Transport Position Sensing Sys-
tem) and drive is commanded.
The lockout cylinders will lock and hold the axle when
drive is not commanded or when the boom is outside the
transport position. The cylinders unlock when pilot pres-
sure is applied to the holding valves mounted on the cylin-
ders and lock when pilot pressure is removed. Pilot
pressure is available from brake pressure and is con-
trolled by a solenoid operated lockout valve mounted in
the frame. To ensure the lockout valve is functioning cor-
rectly, a NO pressure switch is mounted between the lock-
out valve and the holding valves. The system is “healthy”
when pressure trips the pressure switch when the lockout
valve is energized and conversely is healthy when the lack
of pressure resets the pressure switch when the lockout
valve is de-energized.
Failures in the oscillating axle system will cause the con-
trol system to disallow main boom lift up and telescope
out, and tower boom lift up when both booms are within
the transport position and will disallow drive/steer, lift up
and telescope out when either boom is beyond the trans-
port position.
NOTE: For more detailed information concerning system
adjustment and operation, refer to Section 6 - JLG
Control System.
3.11 OSCILLATING AXLE BLEEDING
PROCEDURE AND LOCKOUT TEST
Lockout Cylinder Bleeding
To start the test, the axle must be fully oscillated in one
direction. Start with oscillating the axle so that the left lock-
out cyl. is fully retracted (left front tire up), and the right
lock-out cyl. Is fully extended (right front tire down).
ENSURE PLATFORM IS FULLY LOWERED AND BOOM IS CEN-
TERED OVER REAR AXLE PRIOR TO BEGINNING BLEEDING PRO-
CEDURE. MAKING SURE MACHINE IS ON A LEVEL SURFACE AND
REAR WHEELS ARE BLOCKED, BRAKE WIRE IS DISCONNECTED.
1. Making sure machine is on a level surface and rear
wheels are blocked, machine is in transport mode.
2. Disengage the drive hubs.
3. Use suitable container to catch any residual hydrau-
lic fluid, place container under the lockout cylinder.
4. With the left lockout cyl. retracted, open the bleeder
on top of the cylinder, then have an operator from
the platform (on high engine) feather drive. Activate
drive fully.
5. Close the bleeder when there is a steady stream of
oil and not air.
6. With the axle in the same position, go to the right
lockout cyl. and open the bleeder at the rod end.
Activate drive in the same manner and close when
all air has been purged.
7. Close the bleeder when there is a steady stream of
oil and not air.
8. Oscillate the axle the other direction, left lock-out cyl.
extended (tire down), right lock-out cyl. retracted
(tire up). Use the same procedure for the bleeder in
the rod end of the left lock-out cyl., Then the piston
end of the right lock-out cyl. then close.
9. Repeat this process one more time to ensure that all
air has been purged from the system.
10. Perform oscillating axle lockout test.
11. If necessary, repeat steps 1 thru 9.
NOTE: Bleeding of the oscillating axles is an infrequent
operation performed after hydraulic line failure and or
lock-out cylinder repair.