My Kubota L3901 tractor has had an intermittent issue where the loader will not operate as expected. When the issue persists, the tractor loader will not go down and its also slow & weak lifting.
My L3560 did the same thing, It is your 3rd function poppet valve. I carefully took my valve apart and found fine metal shavings in it. I removed the valve body by unscrewing the four socket head bolts holding the body onto the manifold, then cleaned it out with compressed air. you can also use a small punch with your hand to press down on each end of the spool valve to try to get it centered to see if that works before taking it apart. If the spool is not centered fluid can not return back to the reservoir for the loader hydraulics and keeps them from moving. the hydraulics might still be under pressure when disconnecting the line so be careful of the pressure and the loader coming down, Good luck!
It sounded like it was bypassing. Hydraulic pump was running underload, but nothing was moving. Orange Tractor Talk has several knowledgeable Kubota people over there that may be able to give you a better idea of what is going on and which direction to head to try to fix it.
If it affects the 3 point as well, I’m skeptical that it’s just the third function. The 3 point is probably fed upstream of the loader (mine certainly is). I guess you’ll have to see how it goes!
I didn't get it on video, but the 3 point would raise rapidly to where the lever was set when the tractor was turned off, which added to my suspicion it was an electronic thing. It seemed like as soon as power was cut to the third function, the diverter valve closed and pressure returned elsewhere in the system - in this case, the 3 point.
