Textron JACOBSEN GP400, Technical/Repair Manual

Page: 220 / 354

6-28 4252490-Rev A
HYDRAULICS
6
Field Test Procedures
When a hydraulic system failure occurs, some simple
tests can be performed prior to using test instruments.
The results of these tests can lead you to the suspected
component failure. More extensive test procedures,
using test instruments, are presented later in this section.
(See “Instrument Test Procedures” on page 6-31.)
Preliminary Checks
Perform the following checks prior to beginning any tests.
1. Check the hydraulic oil reservoir for proper fluid level,
the presence of air or water, and unusual odor.
2. Check all hoses, tubes, and fittings for leaks. Tighten
as needed.
3. Eliminate all mechanical issues prior to starting
hydraulic tests.
Lift Cylinder Leakage Test
See Figures 6-18 through 6-20.
NOTE
Front left lift cylinder is shown; procedure is similar for all
lift cylinders.
!
WARNING
1. Start engine. Operate hydraulic system until oil
temperature is 120–150° F (49–65° C).
2. Raise cutting units.
3. Park the mower safely. (See “Park Mower Safely” on
page 1-6.)
4. Support all cutting unit lift arms.
Figure 6-18
5. Disconnect hose (2) from lift cylinder piston end
fitting (1).
6. Install plug in hose (2).
7. Install cap on lift cylinder fitting (1).
8. Remove support from cutting unit lift arm being
tested.
After 15 minutes, does cutting unit drift down?
YES Cylinder is bypassing oil. Repair or replace
lift cylinder. (See “Center Lift Cylinder” on
page 6-52 or “Left and Right Front Lift
Cylinders” on page 6-54.)
NO Repeat the test for all of the lift cylinders. If
all cylinders pass test, the problem may be in
the lift valve. Proceed to step 9.
9. Support all cutting unit lift arms.
10. Connect hose (2) to lift cylinder fitting (1).
11. Start engine and lower the cutting units.
12. Stop engine.
Figure 6-19
The hydraulic system is under pressure, and the
oil will be hot.
• Always relieve pressure in the hydraulic
system before performing service.
• Failure to follow appropriate safety
precautions may result in death or serious
injury.
TN3794
1
2
TN3775
6
5
3
4