JLG 1250AJP Service Manual - Manual (Page 411)

SECTION 5 - HYDRAULICS
3121171 – JLG Lift – 5-57
5.8 DRIVE PUMPS
Troubleshooting Procedure
To aid in troubleshooting, refer also to the pressure mea-
suring port connections for test gauge installation informa-
tion as shown on the hydraulic circuit diagram. Procedure
assumes proper gauges are installed. (Minimum gauges
required: (2) 0-6000 psi, (1) 0-3000 psi & (1) 0-1000 psi
[{2} 0-415 bar, {1} 0-210 bar & {1} 0-70 bar]). This pro-
cedure was written to aid the troubleshooter in following a
logical approach to a hydraulic system fault.
1. Transmission does not propel the machine, diesel
engine running properly
a. Is there oil in the reservoir?
No - Fill reservoir
Yes - If yes, proceed to step 1.b
b. Is the pump input shaft connected to the engine
flex plate or rear of forward pump?
No - Connect pump input shaft
Yes - If yes, proceed to step 1.c
c. Are the hydraulic hoses and tubing connected in
accordance with the hydraulic circuit diagram?
No - Correct the hoses/tubing
Yes - If yes, proceed to step 1.d
d. Is the pump direction of rotation correct? (clock-
wise as looking at the shaft)
No - Fit pump having the correct direction of
rotation
Yes - If yes, proceed to step 1.e
e. Are there "O"-rings missing from fittings (as
example - suction leak), pinched hoses, broken
tubing, etc?
No - Proceed to step 1.f
Yes - Repair damage or fault
f. Are the electrical connectors/wiring intact and
secure to the pump control solenoids?
No - Repair damage or fault
Yes - If yes, proceed to step 1.g
g. Does the engine "labor" when attempting drive,
are the brakes released?
No - Proceed to step 1.h
Yes - Check brake release circuit, measure pres-
sure at port "MP" on Traction Control manifold
h. Are all four wheel drive planetary reduction gear-
boxes engaged?
No - Engage wheel drive(s)
Yes - If yes, proceed to step 2.a
2. Transmission does not propel the machine, diesel
engine running properly - Charge Pump/Relief Valve
a. Is there any charge pressure at port G or indi-
cated by measuring pressure at Ma and Mb?
No - Proceed to step 2.d
Yes - Proceed to step 2.b
b. Is the charge pressure at least 500 psi while run-
ning at high engine speed?
No - Proceed to step 2.c
Yes - Proceed to step 3.a
c. Can the charge pressure be raised by removing
dirt/debris from charge relief poppet or by add-
ing or removing shims from the charge pressure
relief valve mounted in the second pump of the
triple?
No - Proceed to step 2.d
Yes - Adjust pressure to 500 psi +50 psi, -0 psi
(34.4 bar +3.4 bar, -0 bar)
NOTE: The propulsion circuit uses a hot oil flushing valve to
obtain brake release pressure. The hot oil flushing
valve cartridge (#120) is mounted in the Traction
Control Manifold. The flushing valve receives its oil
from the "left side" wheel drive pump; the middle
pump of the triple. With the engine running and pro-
pelling the machine forward or reverse, the "hot oil
flushing valve" and the brake release pressure must
be adjusted to 475 psi, +25 psi, -0 psi (32.7 bar,
+1.7 bar, -0 bar), as set by adjusting pressure relief
cartridge (#130). The brake release pressure must
be 25 psi less than the charge pump pressure. Mea-
sure pressure at port "MP" using a 0-1000 psi (0 - 70
bar) pressure gauge.
d. Is the transmission pumps suction hose pinched
shut?
No - Proceed to step 2e
Yes - Repair damaged hose
e. Is the charge pump suction pressure/vacuum
within recommended limits? (0.8 bar absolute or
6.3 inches of mercury)
No - Proceed to step 2.f
Yes - Proceed to step 2.g
f. Is the suction strainer inside the reservoir
blocked, clogged, restricted?
No - Proceed to step 2.g
Yes - Repair/replace with a clean suction strainer
g. Is the reservoir air breather blocked or
restricted?
No - Proceed to step 2.h
Yes - Clean or replace air breather