JLG G12-55A AccuPlace Service Manual - Manual (Page 25)

3.3 G10-55A & G12-55A AccuPlace
Boom
3.2 BOOM SYSTEM - FOUR SECTION
3.2.1 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 chain
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/
lower cylinder.
3.3 BOOM ASSEMBLY MAINTENANCE
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.
3.3.1 Boom Removal
1. Remove any attachment from the quick switch
assembly.
Note: If replacing the fourth section boom, remove the
quick switch from the fourth section. Refer to Section
3.8.1, “Quick Switch Removal.”
2. Park the machine on a hard, level surface, level the
machine, fully retract the boom, raise the boom,
place the transmission control lever in
(N) NEUTRAL, engage the park brake and shut the
engine OFF.
3. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel, stating that the
machine should not be operated.
4. Open the engine cover. Allow the system fluids to
cool.
5. Remove the battery negative (-) cable from the
battery negative (-) terminal.
6. Support the front of the boom by placing a sling
behind the boom head.
7. Label, disconnect and cap all hydraulic hoses for the
extend/retract and tilt circuits. Cap all fittings and
openings to keep dirt & debris from entering the
hydraulic system.
8. Support the lift cylinder on the left side of the
machine. Remove the lock bolt and rod end pin.
Lower the lift cylinder onto the frame rails. Repeat
this step for the right side lift cylinder.
9. Lower the boom to a level position and place a
suitable support under the boom head. Reposition
the slings to each end of the boom.
10. Remove the boom angle sensors from both the left
and right side of the boom. Refer to Section 9.11.12,
“Boom Angle Sensors.”
11. Remove the bolt securing the boom pivot pin. Pull
out the boom pivot pin.
12. Lift the complete boom off machine and set on level
ground or supports.
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. Failure to comply can result in
death or severe personal injury.