Control valve L555 skidsteer

agb1758c · Jan 20, 2015

I own a L555 New Holland skidsteer. Last year the controls would act like the fluid flow was reversed. It will operate normally, then will reverse the actions of the control, but the response is slow. If I Move the drive controls and bounce the machine, they return to normal. So far I have replaced the small hydraulic pump, cleaned strainer, replaced both filters and changed fluid. I had to replace pump because was unaware that the L555 would airlock and split pump. Its a 1900 psi system and registering just a hair below 1900, like the 1875 area. Is it possible that I have a O-Ring issue inside the control valve and need to rebuild it?

J_J · Jan 20, 2015

Is your valve lever control or solenoid controlled?

If it is a spool valve, you are simply pushing or pulling a spool to connect lands and holes for the fluid to flow in a certain direction.

If it is a solenoid valve, you might have some wires crossed.

What do you mean by air lock?

If your pump IN port is flooded, the pump will push the fluid through all valves until it gets to the tank.

Any reverse flow is by lever or a switch or shorted wires.

agb1758c · Jan 21, 2015

The fluid flow follows the pathway of: pump to control valve (foot levers) to boom solenoid to boom cylinders to oil cooler to chain case. I was wondering if it might not be a loose connection because of the way it would work again if machine was jarred. Thankfully this was built before they got too much into electric and electronic controls. I do know of a wire going to boom solenoid and the seat safety switch (was bypassed before purchase). I will trace the wire for the solenoid and see what I can find and check coil for resistance. On the airlock, for some reason on the L555 if you refilled it with the strainer cap on it will trap air and the pump will not pick up fluid. Someone on the skidsteer forum told me to open the stainer and fill it through the strainer (faster) and would allow air to bleed out and not force fluid out of pump and lose prime is how I understood him. All I know is it worked.

This is the boom solenoid: Screenshot by Lightshot This is the control valve: Screenshot by Lightshot

I hope you can open them. In the mean time I am going to trace wires.

J_J · Jan 21, 2015

I am not sure air is the problem.

Air will expand and collapse due to heat and cooling, and bubbles might form from a suction leak and expand the fluid.

A more likely cause would be a blocked tank vent tube that will cause a vacuum, and might prevent the pump from picking up the prime.

Ivan49 · Jan 22, 2015

I have the same machine and mine did something similar. There is a rod going form the control valve to your foot pedal. Check the holes on the foot pedal end and see if the holes are badly egg shaped. If they are fix them. There is also an adjustment on that rod. With the boom down and the engine off work the foot pedal and see if it is moving the spool all the way in on you control valve. Hope this helps

SSdoxie · Jan 22, 2015

Ivan49 said:
I have the same machine and mine did something similar. There is a rod going form the control valve to your foot pedal. Check the holes on the foot pedal end and see if the holes are badly egg shaped. If they are fix them. There is also an adjustment on that rod. With the boom down and the engine off work the foot pedal and see if it is moving the spool all the way in on you control valve. Hope this helps

Good point. If linkage is worn enough at a picot point it could going over center which would move spool in opposite direction and not have full travel/stroke.

agb1758c · Jan 22, 2015

I haven't thought about that. When the rains let up, I will start checking the easiest first, which would be the linkage. When the hydraulic pump went, I guess I assumed it had to be a hydraulic problem and never checked linkages. As soon as I can check it out I will post what I found. Thanks