JLG 1250AJP Service Manual - Manual (Page 412)

SECTION 5 - HYDRAULICS
5-58 – JLG Lift – 3121171
h. Remove charge pressure relief valve from the
middle pump and inspect. Is it damaged?
No - Refit cartridge and proceed to step 2.i
Yes - Clean & inspect cartridge, poppet, springs,
seals to determine cause of damage. Repair or
fit a new cartridge and return to step 2.a
i. Remove and inspect charge pump assemblies.
Are they damaged?
No - Proceed to step 2.j
Yes - Repair and/or replace damaged compo-
nents and return to step 2.a
j. Is the charge pump installed for the clockwise
rotation?
No - Refit charge pump. Return to step 2.a
Yes - With proper charge pressure and transmis-
sion still does not operate, proceed to step 3.a
3. Transmission does not propel the machine, diesel
engine running properly - Pump Control: (Insure
Generator Drive option is not turned "on")
a. Are the electrical connectors & wiring connected
properly to the pump control solenoids?
No - Connect a ammeter in series with solenoid
wiring. Is a current of 400 mA to 1060 mA being
applied. (Current signal varies with joystick posi-
tion)
Yes - Proceed to step 3.b
b. Are all four of the two-speed motors, mounted in
the wheel drive planetary reduction gearboxes,
shifted to maximum displacement (high torque -
low speed)?
No - Select maximum displacement
Yes - Proceed to step 3.c
c. Actuate the pump control in both directions. Do
the pumps stroke? Do they go to full stroke?
No - Refer to the pump service manual and then
proceed to step 3.d
Yes - Operate the transmission
d. Remove stroking orifices in X
1
and X
2
. Install
pressure gauges in X
1
and X
2
(0-500 psi [0 - 35
bar]). Stroke the pump in both directions. Do
the pressures at X
1
and X
2
alternate between 30
& 250 psi (2 & 17 bar)?
No - Remove the EP control module & replace it
with a new unit. Repeat step 3.c
Yes - Proceed to step 3.e.
e. Is the pressure at port "R", case pressure, less
than 15 psi (1 bar) gauge pressure?
No - Correct problem restricting case drain oil
flow (oil cooler blockage, pinched hoses, etc)
Yes - Proceed to step 3.f
f. Stroke pump in both directions, while measuring
pressure at Ma & Mb ports of the pump. Does
any pressure greater than charge pressure alter-
nate between ports Ma & Mb?
No - Verify that loading the pump will cause sys-
tem pressure to increase above charge pres-
sure. Proceed to step 3.a
Yes - Proceed to step 3.g
g. Is it possible to adjust high pressure relief valves
using 0-6000 psi (0 - 415 bar) gauges to monitor
pressure at Ma & Mb? (Refer to relief valve
adjustment)
No - Replace high pressure relief valve and
return to step 3.c
Yes - Adjust high pressure relief valves to 5000
psi +50 psi, -0 psi (344.7 bar +3.4 bar, -0 bar)
h. Actuate control in both directions. Does trans-
mission operate?
No - Check that minimum displacement stops
on the wheel drive motors are adjusted properly,
check that the motors stroke between maximum
to minimum.
Yes - Operate the transmission
4. Transmission Drive is Sluggish or Erratic
a. Does the "EP" proportional pump control current
vary with joystick movement?
No - Rectify the problem - broken wires, electri-
cal connector, open solenoid coil, etc.
Yes - Proceed to step 4.b
b. Are all four (4) brakes fully released?
No - Check brake release pressure and insure
each wheel receives correct release pressure.
Yes - Proceed to step 4.c
c. Are the pumps stroking time orifices installed
tight and clean?
No - Remove the Plugs in ports X
1
and X
2
.
Remove orifices with a 3mm allen wrench.
Check that orifices are clean & re-install.
Yes - Proceed to step 4.d
d. Is an motor displacement stroking time orifice
plugged or is the two-speed shift hose pinched?
Yes - Inspect and clean stroking orifice, check
two-speed hose routing
e. Is a flow divider/combiner cartridge stuck in the
Traction Control Manifold? Flow divider/com-
biner cartridge # 111 controls the right side
wheels, # 112 controls the left side wheels. Also
check to insure bypass orifices #151 (right side)
and # 152 (left side are not plugged.