Case 435 Repair Manual page 71

DISTRIBUTION SYSTEMS - PRIMARY HYDRAULIC POWER SYSTEM
14. After you get the correct charge pressure in
NEUTRAL, do the following steps:
A. Start and run the engine at low idle. Increase
the engine speed to full throttle. Slowly move one
of the direction control levers FORWARD to load
the hydrostatic piston pump and drive motor without
decreasing the engine speed. DO NOT Lug the
Engine. Reduced engine speed causes decreased
charge pump flow, which will affect the pressure
readings. Repeat for the opposite side (only move
one lever at a time).
B. Read the pressure gauge. The pressure must
be within 138 kPa (1.5 bar) (20 psi) of the pressure
in step10.
C. Repeat Steps A and B with the direction control
levers in REVERSE.
Interpretation of the results:
Once the charge pressure meets specifications
with the levers in the neutral position, compare
the pressure readings under load with the neutral
readings. The readings should be highest with
the levers in the interposition, for this is when the
direct acting charge relief has to handle the greatest
amount of oil flow. With thinning at full throttle, the
maximum difference in charge pressure readings
between the system in neutral endwise the system
loaded in both directions must be not greater than
138 kPa (1.5 bar) (20 psi). Any difference greater
than 138 kPa (1.5 bar) (20 psi) indicates excessive
leakage from the closed loop, which will require
repair.
NOTE: The charge pressure drop indicates internal
leakage from the system with the system under load. This
is caused by less oil flowing over the charge relief and
therefore, the lower pressure. Excessive leakage (greater
than 138 kPa (1.5 bar) (20 psi) will result in slower drive
speed on that side of the machine, but depending on what
is damaged in the system, the leakage may only show up
under heavy load conditions.
NOTE: To determine if the problem is in the pump or the
motor do the following:
15. On the side (left or right) that the charge pressure
dropped more than 138kPa (1.5 bar) (20psi), cap
the two high-pressure lines that supply the drive
motor. The lines can be capped at either the pump
or at the motor, which ever is easiest.
16. With the lines capped to the drive motor, start and
run the engine at low idle. Increase the engine
speed to full throttle. Slowly move the direction
control lever that is being tested FORWARD to load
the hydrostatic piston pump without decreasing the
engine speed. DO NOT Lug the Engine. Reduced
engine speed causes decreased charge pump flow,
which will affect the pressure readings.
17. Read the pressure gauge. The pressure must be
within 138 kPa (1.5 bar) (20 psi) of the pressure in
step 10.
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