JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-16 – JLG Lift – 3121160
Bleeding
1. Install brake in system and connect pressure lines.
2. Bleed pressure release section of brake by pressur-
izing side inlet port and allowing air to escape from
top port. Pressure should not exceed 6.9 bar (100
psi) during bleeding.
3. Apply sufficient pressure to release brake and check
for proper operation in system.
Table 3-2. Troubleshooting
PROBLEM CAUSE EXPLANATION ACTION
Brake slips Excessive pressure in hydraulic system If there is back pressure in the actuation
line of the brake, holding torque will be
reduced. Check filters, hose size, restrictions in
other hydraulic components.
Oil in brake if designed for dry use Wet linings generate 67% of the dry
torque rating. If the brake has oil in it,
check the type of oil hydraulic or gearbox.
1. Gearbox oil
2. Hydraulic oil Replace oil seal in brake.
Check motor seal
Check piston seals
NOTE: Internal components will
need to be inspected,
cleaned and replaced as
required.
Disc plates worn The thickness of the disc stack sets the
torque level. A thin stack reduces torque. Check disc thickness.
Springs broken or have taken a perma-
nent set Broken or set springs can cause reduced
torque - a rare occurrence. Check release pressure. (See spring
replacement).
Brake drags or runs hot Low actuation pressure The brake should be pressurized to mini-
mum of 1.38 bar (20 psi) over the full
release pressure under normal operating
conditions. Lower pressures will cause
the brake to drag thus generating heat. Place pressure gauge in bleed port &
check pressure with system on.
Bearing failure If the bearing should fail, a large amount of
drag can be generated. Replace bearing.
Brake will not release Stuck or clogged valve Brakes are designed to come on when
system pressure drops below stated
release pressure. If pressure cannot get to
brake, the brake will not release. Place pressure gauge in bleed port -
check for adequate pressure. Replace
inoperative line or component.
Bad o-rings If release piston will not hold pressure,
brake will not release. Replace o-rings.
Discs frozen These brakes are designed for only lim-
ited dynamic braking. A severe emer-
gency stop or prolonged reduced release
pressure operation may result in this type
of damage. Replace disc stack.