JLG 534D-10 - Manual (Page 49)

3.21 534D-9, 534D-10 & 544D
Boom
3.9 BOOM SYSTEM - FOUR SECTION
3.9.1 Boom System Operation
The four section boom consists of the first, second, third
and fourth assemblies with double third and fourth
section extend chains, a double third section retract
chains and a single fourth section retract chain.
As the extend/retract cylinder, which is anchored at the
front of the second boom section, and the rear of the first
boom section begins to extend, it forces the second boom
section out of the first boom section.
The boom sections are connected by extend and retract
chains. These chains are routed around sheaves on the
second and third boom sections. As the second section is
forced out hydraulically, the third and fourth boom
sections are pulled out by the extend chains.
As hydraulic pressure is applied to the retract port on the
extend/retract cylinder, the second boom section is pulled
back into the first boom section, and the retract chain
pulls the third and fourth boom sections back into the
second boom section.
This mechanical linkage formed by the chains and
supporting hardware, extends and retracts the third and
fourth boom sections at the same rate.
The boom section lifts and lowers via action of the lift
cylinder.
3.10 BOOM MAINTENANCE - FOUR
SECTION (COMPLETE REMOVAL)
These instructions must be completed in sequence. The
second, third and fourth boom sections are removed from
the first boom section.The third and fourth boom sections
are removed from the second boom section.The fourth
boom section is removed from the third boom section.
Before beginning, conduct a visual inspection of the
machine and work area, and review the task about to be
undertaken. Read, understand and follow these
instructions.
3.10.1 Boom Removal
1. Park the machine on a hard, level surface, fully
retract the boom, lower the boom to a level position,
place the transmission control lever in (N)
NEUTRAL, engage the park brake and shut the
engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel, stating that the
machine should not be operated.
3. Open the engine cover. Allow the system fluids to
cool.
4. Remove the battery negative (-) cable from the
battery negative (-) terminal.
Note: When removing a complete boom assembly use
a hoist or crane with a minimum lift capacity of 8500 lbs.
5. Fasten suitable slings to each end of the first boom
section making sure a balance point is achieved.
6. Take the weight off the complete boom assembly.
7. Identify and tag all hydraulic hoses and electrical
cables.
8. Loosen and separate all hydraulic hoses and
electrical cables. Plug the hose ends and tube ends
to prevent dirt and debris from entering the hydraulic
system.
9. With the cylinder hoses blocked off, the boom
sections will be locked in position, preventing run
out.
10. Remove the lock bolts and pins from the rod ends of
the compensation and lift cylinders.
11. Confirm that the crane has the weight of the boom.
12. Remove the lock bolt and boom pivot pin.
13. While lifting the boom assembly, make sure the
compensation and lift cylinders are properly
supported.
14. Lift the complete boom assembly free of the
machine and place on the ground or suitable
supports.
3.10.2 Extend/Retract Cylinder Removal
With the boom assembly now turned upside down, the
extend/retract cylinder is easily removed.
1. Attach a suitable sling to the extend/retract cylinder
(1) and take the weight off the cylinder to aid in pin
removal.
2. Remove the extend/retract cylinder support (2) from
the front of the extend/retract cylinder.
WARNING
NEVER weld or drill the boom unless approved in
writing by JLG. The structural integrity of the boom
will be impaired if subjected to any repair involving
welding or drilling.