JLG 1100S Service Manual - Manual (Page 256)

SECTION 5 - HYDRAULICS
5-34 – JLG Lift – 3121256
f. Is a wheel drive hydraulic motor operating at
excessive speed?
Yes - Check minimum displacement stop screw
adjustments on the motors. Should be 0.433" or
11mm above the stop screw lock nut. Is one or
more motors "stuck" at minimum displacement,
check for plugged/blocked two-speed stroking
orifice(s).
9. Transmission Operates at a Higher than Normal
Temperature
a. Is the reservoir temperature above 195 o F (90.5°
C)?
No - 195
o F (90.5° C) is the upper limit. If temper-
ature is over 195 o F (90.5° C), the oil cooler may
need to be cleaned.
Yes - Proceed to step 9.c
b. Are the hydraulic motor(s) stalling (wheels not
turning) intermittently?
No - Proceed to step 9.c
Yes - Hydraulic fluid is being heated through
system pressure relief valves. Shut down system
and rectify the cause of motor stall.
c. Does oil temperature remain above 195 o F (90.5°
C), after cleaning the oil cooler?
No - Operate transmission. Check oil cooler
more often.
Yes - Proceed to step 8.a
10. Transmission Operates at a Higher than Normal
Temperature
a. Check for differential temperature across the oil
cooler. Is there a temperature difference?
No - Check to determine if the bypass check
valve (10 psi [0.7 bar] crack pressure) is stuck
open. Check to determine if the oil cooler is
restricted internally, causing oil flow to pass
across the bypass check valve.
Yes - Proceed to step 8.b
NOTE: Oil cooler flow is received from the transmission
pumps cases, max. continuous pump case pressure
is 15 psi gauge pressure. Higher pressure will pre-
maturely damage pump shaft seals
b. Disconnect pump case drain from oil cooler &
check flow rate from charge pumps. Is the flow
rate 3.8 GPM (14.4 LPM) with diesel idle speed
of 1200 rpm?
No - Refer to charge pump removal & inspection
procedure
11. Transmission Pump(s) Do Not Develop Maximum
Horsepower (Flow & Pressure)
a. Does the charge pump pressure meet specifica-
tion?
No - Return to step 2.a
Yes - Proceed to step 11.b
b. Does the pump case pressure exceed 15 psi
gauge pressure?
No - Proceed to step 11.c
Yes - Check case drain hoses, oil cooler, etc. for
pinched or restricted oil flow
c. Are the pump(s) high pressure cross port relief
valves adjusted to the required pressure (5000
psi) so they do not bypass prematurely?
No - Inspect/clean/adjust and or replace valve
cartridge
Yes - Replace the pump, after blocking the "A" &
"B" ports, running the pump and measuring
pressure developed at "A" & "B". This must be
done to insure that flow & pressure loss in not
elsewhere in the system. (motors, swivel cou-
pling, etc)
d. Is the diesel engine capable of developing
horsepower at design rpm?
Follow recommended troubleshooting proce-
dures to insure the engine is developing full
power at specified rpms.
Charge Pressure Relief Valve Adjustment
With a low pressure (0 – 1000 psi [0 - 70 bar]) pressure
gauge tee’d into the ”G” port or two (2) low pressure
gauges installed into ”Ma” and ”Mb”, run pump at engine
idle speed. Do not place the pump on stroke – low pres-
sure gauges installed in ”Ma” & ”Mb” will be damaged!
Prior to adjusting pressure, insure charge pressure relief
valve is clean of any dirt or debris. The charge pressure
relief valve does not wear appreciably over time. If charge
pressure was normal and then has decayed, check for
other causes of low charge pressure. If pressure is low,
remove relief valve and add shim(s). If pressure is high,
remove relief valve and take out shim(s).
CHARGE RELIEF