1. Inspect Manual Displacement Control
Disconnect the external control linkage from the control
handle and check for neutral operating with control handle.
Releasing control handle should allow the pump to return to
neutral. If operation is satisfactory with external control
linkage disconnected, the problem is not in the hydrostatic
If operation is not satisfactory with external control linkage
disconnected from control handle, the control may be
misadjusted. Adjustment procedures are contained in this
adjustment the following inspection is
Remove the cap screws holding the control in place, and
swing it away from housing and remove. Inspect visible
linkages, torsion spring, and O-rings. Inspect for missing,
plugged, or improper orifice.
2. Inspect System Relief Valves
interchange the relief valve cartridges to see if the problem
changes to the other direction. If so, one relief valve
cartridge is either malfunctioning or does not have the
proper setting. The first two (2) digits of the pressure
setting are stamped on the end of the cartridge. Compare
to machine specification.
The relief valves are factory set and
should not be disassembled further.
3. Inspect Shuttle Valve
Remove the two (2) hex plugs and the shuttle valve parts.
orientation. Washers must go between spool and springs.
Inspect to see if spool moves smoothly in its bore.
The spool and manifold are matched
and cannot be replaced separately.