Kx121-3ss thumb power

[NikonRon]

How can I increase thumb holding power? Ron

 

[dfkrug]

If you can locate the AUX valve that controls the thumb, it may have its own
relief valve. Sometimes they are adjustable. If you have an OEM setup, your
manual may have a hyd schematic.

If you want to mess around with relief valve settings, I suggest you get a
pressure test gauge, if you do not have one.

 

[NikonRon]

I'll look a bit deeper and see if I can locate the AUX valve. Ron

 

[bcp]

Assuming a cylinder is operating to its full system ability, but is weak, in general, you can go up a size in cylinder diameter, or move the thumb cylinder pin farther from the hinge pin. But the second option would change the thumb swing arc some.

Does yours look like this?



Bruce

 

[NikonRon]

It will hold the load if I hold the button but if I release it it seems to back off on pressure. Appears to be OEM Kubota. Ron

 

[Code54]

Just for reference I have a KX91 and if I clamp down with the thumb then let off it continues to hold and does no back off. Sounds like something is leaking down more than you are not getting enough initial pressure. The thumb needs to be set so the bucket can overpower it so the machine does not get damaged.

 

[NikonRon]

I need to pick up 1200# rocks and would like for it to hold its grip. Aware that the bucket should be able to push it back which also lets you curl the bucket as you position items. Is there a way to adjust the pressure? Ron

 

[NikonRon]

Upon further inspection I have found that it is a USA Attachments after market thumb. Ron

 

[Code54]

Before adjusting pressure you need to check the pressure and see if it is in spec. From what you are saying it does not sound like pressure is your problem, but bleed down is the issue.
Open your cover over the hydro tank - there should be a lever (valve) there on the tank or close to it. This controls the thumb in your case - if it get a little out of position the thumb will bleed off pressure. You normally use this lever to switch between a thumb and a breaker. Check that and see if it helps.

 

[NikonRon]

I'll take a look and see if I can locate it, thanks. Ron

 

[NikonRon]

There's no lever at or near the hydraulic tank. Ron

 

[dfkrug]

Just for reference I have a KX91 and if I clamp down with the thumb then let off it continues
to hold and does no back off.

Is that the way Kubota generally does it with OEM thumb control on mini-Xes?

My only experience with OEM hyd thumbs on a Mini-X is with a Takeuchi. In that case, there
was a foot pedal which closed the thumb when you pushed it, and retracted the thumb when
the pedal was released.

If the OEM hyd thumb can be pushed back, while stationary, with bucket force, there is also
a "work port RV" on the valve. In addition to some sort of system RV.

 

[NikonRon]

I don't know that it actually backs off, I just don't think that it is applying enough force to hold a load. The Kubota has a thumb operated push button with push to close and push to open. Ron

 

[Code54]

How old is the 121? All the newer machines have a level that lets you switch the flow for breakers or a thumb. See attachment to give you a better idea.

Yes - the factory sets the thumb system up so the bucket can "push" it back - lets you curl and grab better. My 91 will grab a 4x4 and snap it right in half before the bucket ever pushes the thumbs back. It has a LOT of clamping force. While learning the machine it was not uncommon to break rocks by squeezing them too tightly - had to learn a light touch.

 

[NikonRon]

2009 model. Ron

 

[Code54]

I also think you can select flow through the joystick/service port setting. Not sure if that would have anything to do with it but may want to check your book. It looks like an 09 should have a selector lever near the tank. This manual shows it and it is a 2007. My 2015 is still the same setup.
Hope it helps

 

[NikonRon]

Come daylight I'll have to look again, thanks. That looks to be just a ball valve in the circuit. Ron

 

[Code54]

Basically is - Mine got a shade out off position one time and my thumb started to act very weird. I have a zip tie on mine so it cant change position, think the jarring around let it move a shade. Good luck!