JLG M450 Service Manual - Manual (Page 50)

SECTION 3 - CHASSIS & TURNTABLE
3-10 – JLG Lift – 3121829
Table 3-2. Drive Brake Diagnosis
Problem Cause Explanation
Corrective
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.
Springs broken or have taken a
permanent set Broken or set springs can cause reduced torque -
rare occurrence. See spring replacement
Brake drags or runs
hot Low actuation pressure The brake should be pressurized to minimum 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 fall. 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 pres-
sure drops below stated release pressure. If pres-
sure cannot get to brake, the brake will not release. Place pressure gauge in bleed port
- check for adequate pressure.
Replace defective line or compo-
nent.
Bad o-rings Release piston will not hold pressure, brake will not
release. Replace o-rings.
Discs frozen These brakes are designed for only limited dynamic
braking. A severe emergency stop or prolonged
reduced release pressure operation may result in
this type of damage. Replace disc stack.