Oshkosh JLG 1500SJ, Service And Maintenance Manual

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SECTION 5 - BASIC HYDRAULIC INFORMATION & HYDRAULIC SCHEMATICS
3121262 – JLG Lift – 5-133
f. Is a wheel drive hydraulic motor operating at exces-
sive 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 Temper-
ature
a. Is the reservoir temperature above 195
o
F (90.5° C)?
No - 195
o
F (90.5° C) is the upper limit. If temperature
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 turn-
ing) 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 Temper-
ature
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 prematurely 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 Horse-
power (Flow & Pressure)
a. Does the charge pump pressure meet specification?
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 car-
tridge
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 sys-
tem. (motors, swivel coupling, etc.)
d. Is the diesel engine capable of developing horse-
power at design rpm?
Follow recommended troubleshooting procedures
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 pressure 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 pres-
sure is low, remove relief valve and add shim(s). If pressure is
high, remove relief valve and take out shim(s).
CHARGE RELIEF