JLG G12-55A Service Manual - Manual (Page 38)

Boom
3-4 G10-55A, G12-55A
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 provide the complete boom assembly
removal and installation or the second, third and fourth
boom sections removal and installation.
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.The boom assembly consists of the first,
second and third section booms and supporting
hardware.
Note: Before removing the boom or boom section, the
carriage or any other attachment must be removed from
the quick switch.
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.
During service of the boom, perform the following:
1. Check wear pads. (Refer to Section 3.11, “Boom
Wear Pads.”)
2. Check hose sheaves and chain rollers.
3. Apply grease at all lubrication points (grease fittings).
(Refer to Section 2.6, “Lubrication Schedules.”)
4. Check for proper operation by operating all boom
functions through their full ranges of motion several
times.
Depending on your particular circumstance, the following
procedures explain the removal/installation of individual
boom sections or removal/installation of the complete
boom
.
WARNING
NEVER weld or drill the boom unless approved in
writing by the manufacturer. The structural integrity of
the boom will be impaired if subjected to any repair
involving welding or drilling.