JLG 800A_AJ Service Manual - Manual (Page 226)

SECTION 4 - BOOM & PLATFORM
4-12 – JLG Lift – 3120858
Tower Out of Sync
Tower is out of sync backwards, upright leaning toward
the platform.
When towering down the upright cylinder bottoms out
before the lower lift. Problems that could cause this are:
1. The releveling valve (red knob on the oil tank P/N:
4640866), this is a poppet valve that could be leak-
ing fluid out of the closed loop. Manually opening
the valve and flushing it can eliminate any contami-
nate on the seat. The seat could also be damaged,
so replacing the cartridge might be necessary.
2. A relief valve is located in the upright (P/N:
4640929). This relief valve could be leaking back-
wards out of the loop. Replace the cartridge. They
are pre-set.
3. The counter/balance valve in the piston end of the
upright level cylinder. There could be a leak path
from the valve port to the pilot port. Replace the
counter/balance valve.
4. The counter/balance valve in the rod end of the
lower lift cylinder. There could be a leak path from
the valve port to the pilot port. Replace the counter/
balance valve.
5. The packing on either the upright or lower cylinder
can cause this. Do cylinder tests to determine if
either cylinder needs new packing.