Kubota b21 3 point problem

[Ozarkorange]

My b21 has lost lifting power to 3 point arms. It will lift arms with no weight attached. All other hydraulics are working fine. The control knob seems to be working properly and will lock arms in place when closed. The selector rod for 3pt/ backhoe seems to be working properly and will drop arms when backhoe is selected. When I attach backhoe all those functions work correctly as well. i Also noticed that when 3 pt arms are in raised position and I use loader to pick front of tractor off the ground the arms will fall until I release loader lever. I have changed both hydraulic and transmission filter and oil, cleaned in tank screen, and taken pressure relief valve apart to look for any trash. Has anyone else had this issue and resolved it? Any help would be greatly appreciated!

 

[rScotty]

Did it ever have lifting power to the 3pt arms? If it worked, what might have caused it to change? Do you have the operator's manual? BTW, congrats on all the oil, filter, and screen cleaning. That takes care of the simple things.

Obviously I'm guessing, but that's because I don't know the particulars on the B21. Lots of owners here. You might want to move the question to the Kubota forum so more B21 owners will see it.

Could it be a problem with the selector rod. Or rods... does the B21 have one rod or two? Our M59 has two selector rods.

 

[Ozarkorange]

Thanks for the reply.. it did work and failed while I had box blade on it.. had to disconnect and carry back to house with the loader. I do have the operators manual but not the workshop manual. I am trying to eliminate everything short of it being the piston seal as it is enclosed in the housing

 

[rScotty]

Thanks for the reply.. it did work and failed while I had box blade on it.. had to disconnect and carry back to house with the loader. I do have the operators manual but not the workshop manual. I am trying to eliminate everything short of it being the piston seal as it is enclosed in the housing

You did say that the control knob was working properly and would lock the arms in place. My assumption - maybe false - was that the control knob is actually a needle valve that can trap fluid held by the 3pt piston. At least that is the way that some of them work. If the seal was bad there would be an alternate path and would the control knob still work?

You may need that workshop manual. What year is the B21?

 

[Ozarkorange]

I see what your saying there..it is a 1998

 

[Ozarkorange]

This is the control valve

 

[rScotty]

That looks typical.

As I understand it, on yours the problem is that you can lift the arms manually and they will just fall down. If the control valve #280 in illustration 1 is working properly, then screwing it in should reduce the speed of the fall and screwing it in all the way should hold the arms in position. At least that is how it should work if everything connected to shaft #220 is doing its job and the 3pt piston seal is intact.

There was a thread not long ago where the securing nut that holds part #170 to the end of shaft 220 had come adrift. The result was that part 170 was left behind when the shaft was unscrewed. For awhile the owner thought that it was missing but finally saw it in the hole and was able to hook it and pull the parts out.

Coming apart like that had caused his odd lifting problems even though it still did work to lock the arms. Anyway, that is pretty simple to check. I'd do that & then try to dream up some more experiments before taking anything else apart.
It could be a problem in the main 3 pt control valve - but problems inside that valve seem to be rare.

 

[Ozarkorange]

I will definitely check that out. Thank you for your input.

 

[Ozarkorange]

rScotty I think you were absolutely right with the problem being in control valve as when I close it it with piston arms raised it it is locked in place and doesn’t bleed off. That should eliminate piston seal at least. Unfortunately it is enclosed in same housing as piston that also has transmission shifter going into it.. I ordered workshop manual and will see how to proceed with disassembly. Thanks for the advice