Kubota KX80-4 Thumb cylinder drops

[mauizook]

Aloha and thanks for checking this post out. I hope that someone will be able to give me a good lead to fix my hydraulic issue.
I was operating my 2018 machine yesterday and all of a sudden the thumb fell down while I was using the bucket. It didn't slam down, but gradually fell making the full travel in about 10 seconds. I checked that the hammer valve under the hood was in the correct position. I can use the button on the joystick to lift it back up and to grab. If I have the bucket curled up the thumb stays put because gravity keeps it in the up position. I was lucky to be almost finished with the job when the incident occurred. Once I get it back to the farm I will be able to troubleshoot more.

 

[uffex]

Good day
I suggest you begin check the thumb cylinder out for seal failure.
Kind regards
Uffex

 

[uffex]

Good day
While the information refers to the bucket cylinder, the principle is the same for the thumb cylinder.
Kind regards
Uffex

 

[mauizook]

Thanks for responding Uffex. I got the machine back to the farm and switched the cylinder hoses to the other auxiliary lines and the cylinder works perfectly. I assume my relief valve is not working properly. Is that a safe assumption?
On the original auxiliary lines, with the relief valve set to open at 2150 psi to protect the thumb cylinder, the thumb open circuit moved quite slowly with no oomph and the circuit to grab with the thumb moved with gusto. It wouldn't drift into the open position, but it would drift into the closed position.
Does that sound like relief valve to you or is it possible that there is another issue? Thanks

 

[uffex]

Good day
Your post suggests a issue with the port relief valve, Im not sure which you have connected so I have pointed out both options. If you are not sure follow the leaking line back to the MCV it will connect directly to the leaking valve. See attched.
Kind regards
Uffex

 

[mauizook]

Yes, exactly, that is my thought as well. I've looked at the valve bank and determined that is either one of those valves that is in question. I suspect it is the one with 5 and 6 reference numbers because it is the only relief valve that has some of the gray paint broken off like it has been adjusted in the past. The thumb cylinder has a big sticker on it that says relief valve must be adjusted to 2150 psi. I'll let you know what i find out when i get my test gauges.
Thanks

 

[mauizook]

I finally got to my exavator and i popped out the relief valve. It was stuck open. pushed it back in and I'm back in business. Thanks for the guidance.