SERVICE MANUAL
Paragraphs 128-129
HYDRAULIC LIFT SYSTEM
The hydraulic lift system provides load (draft)
and position control in coiyunction with the 3-
point hitch.
The load (draft) control is taken from the third
(upper) link and transferred through a bellcrank
on the torsion bar and linkage to this draft con-
trol valve located in the hydraulic lift housing.
The externally mounted torsion bar is located on
the rear side of the lift unit.
The hydraulic lift housing, which also serves as
the cover for the differential portion of the trac-
tor rear main frame, contains the work cylinder,
rockshaft, valves and the necessary linkage. Aux-
iliary valves (either one, two or three), on trac-
tors so equipped, are mounted on right side of the
lift housing. The pump which supplies the hydrau-
lic system is attached to the multiple control valve
(MCV) which is mounted on left side of rear frame.
Pump is driven by a gear on the rear of pto driv-
en shaft. The oil used in the hydraulic system is
drawn from the rear main frame and through a
full-flow filter which is a part of the
MCV
on left
side of rear frame.
TROUBLE SHOOTING
All Models
128.
The following are symptoms which may oc-
cur during operation of the hydraulic lift system. By
using this information in coi\junction with the TEST
and ADJUST information, no trouble should be en-
countered in servicing the hydraulic system.
1.
Hitch will not lift. Could be caused by:
a. Faulty main relief valve.
b.
Faulty cushion relief valve.
c. Internal linkage disconnected.
2.
Hitch Ufts when auxiliary valve is actuated.
Could be caused by:
a. Unloading valve orifice plugged.
b.
Unloading valve piston sticking.
c. Unloading valve body assembly not seating
or body assembly loose.
3.
Hitch lifts very slowly. Could be caused by:
a. Unloading valve leaking.
b.
Excessive load.
c. Faulty main relief valve.
d. Faulty cushion relief valve.
e. Work cylinder or piston scored or **0" ring
faulty.
f. Flow control valve stuck in slow position.
g. Faulty pump.
4.
Hitch will not lower. Could be caused by:
a. Main control valve spool sticking or spring
faulty.
b.
Drop poppet **0'' ring is damaged or drop
poppet is sticking.
5.
Hitch lowers very slowly. Could be caused by:
a. Action control valve spool or piston
sticking.
b.
Action control valve linkage maladjusted.
c. Drop poppet valve
**0*'
ring damaged.
6. Hitch lowers too fast in action control zone.
Could be caused by:
a. Improper adjustment of action control
valve.
7.
Hitch will not maintain position. Could be
caused by:
a. Work cylinder or piston scored or piston
'*0"
ring damaged.
b.
Cylinder cushion relief valve leaking.
c. Drop poppet check valve ball not seated.
d. Drop poppet ball seat binding in the drop
poppet.
8. Hydraulic system stays on high pressure.
Could be caused by:
a. Linkage malacyusted, broken or discon-
nected.
b.
Auxiliary valve not in neutral.
c. Mechanical interference.
9. System stays on high pressure after lifting
load, but returns to low pressure after slight
movement of position control lever toward
**LOWER*' position. Could be caused by:
a. Leak in piston side of unloading valve
circuit.
10.
Hitch senses with load control in **OFF" po-
sition. Could be caused by:
a. Improper ac^ustment of load sensing
linkage.
TEST AND ADJUST
All Models
129.
Before proceeding with any testing or at^ust-
ing, be sure the hydraulic pump is operating satisfac-
torily, hydraulic fluid level is correct and filter is in
good condition. All tests should be conducted with
hydraulic fluid at operating temperature of at least
100° F (38° C). Cycle system, if necessary, to ensure
87
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