JLG 740AJ Service Manual - Manual (Page 233)

SECTION 4 - BOOM & PLATFORM
3121160 – JLG Lift – 4-17
Tower is out of sync forwards, upright leaning toward
the steer axle.
When towering down, the lower lift cylinder bottoms out
before the upright level cylinder. This is caused by too
much oil between the two cylinders. Problems that could
cause this are:
1. The relief valve located in the upright (P/N:
4640929). If this valve is set too low or has contami-
nate in it causing it to leak prematurely, when lifting
down oil can pass through it causing the volume to
grow between the cylinders. Flush the valve out and
reinstall it, or replace the cartridge. The cartridge
pressure is pre-set so no adjustment can be made.
2. The counterbalance valve in the piston end of the
upright level cylinder. There could be a leak path
from the pilot port to the valve port. Replace the
counterbalance valve.
3. The counterbalance valve in the rod end of the lower
lift cylinder. There could be a leak path from the pilot
port to the valve port. Replace the counterbalance
valve.
4. The packing on the lower lift cylinder can cause this.
Do a cylinder test to check this out. Refer to Section
2.4, Cylinder Drift Test.