JLG 740AJ, Service And Maintenance Manual

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SECTION 4 - BOO M & PLATFOR M
3121160 4-21
3. The counterbalance 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
counterbalance valve.
4. The counterbalance 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 counterbalance valve.
5. The packing on either the upright or lower cylinder can
cause this. Do cylinder tests to determine if either cylin-
der needs new packing.
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 contaminate in it causing
it to leak prematurely, when lifting down oil can pass
through it causing the volume to grow between the cyl-
inders. Flush the valve out and reinstall it, or replace the
cartridge. The cartridge pressure is pre-set so no adjust-
ment can be made.