Steering orbitrol Ognibene STON80

T4S
The tractor pulls to the left at full engine speed on the tarmac road.
Cause: The controlled pressure from the PS valve can be transferred to the power steering cylinder by the Danfoss unit via suction valves

Production solution
A different steering valve without a post-suction valve must be used.
The part number of the new steering valve is 5195514 (170 bar).
Modified serial numbers from production:
For NA markets;
NH: ELRT4S75LNAX00074, CIH: ELRFA75ALNAY00100.
For EU markets:
NH: ELRT4S75ANX102062, CIH: ELRFA75AKNY100996.

Field solution
The new steering valve can be retrofitted on site.
Carry out the following steps before replacing the current steering valve.
1) Ensure correct toe-in and correct preload/movement of both front wheel hubs. Check each side independently for any stiffness.
2) Lift the front wheels off the ground and start the engine to see if the wheels turn to the left by themselves.
3) Check that the control pressure is 18 bar.
4) Check the pressure in the right and left control lines:
With part number 5195514 it should be 0 bar.
With 5195514 it should be 0 bar.
5) If the steering cylinder seals suspect that the steering is turning fully to one side, disconnect the steering line from the port closest to the piston and plug the line. Keep trying to turn in the same direction to check whether the seal is leaking.
The illustration below shows a comparison of the hydraulic diagram between the current and the new steering unit.