Thumb problems KX-71

[Someotherguy]

Hello.
Im having problems with my thumb.
It has good clamping pressure and speed, but the return is week to non existant. I swaped the hoses and the problem followed,
as in the clamping pressure was nil and the return was fast. Way to fast.
In the pics you can see the block that the hoses attach to. The larger pipe feeds the bottom of the cylinder.
The thumb will creep down after I shut off the machine.
Any ideas guys?
Jason

 

[materthegreater]

Does that have the electronic thumb control on the right joystick? If that switch on the joystick gets too dirty it won't make a good connection to open the hydraulic valve.

 

[Someotherguy]

The machine is a 1994 so no joystick, just leavers.
The thumb control is a foot pedal on the floor.
Jason

 

[materthegreater]

Hmm. I dunno what it would be then. Maybe a bent and crimped pipe?
Have you watched the valve to make sure that it moves fully in both directions when moving the foot pedal?

 

[Someotherguy]

The pipes seem fine. I dont see any valve moving. When you say valve moving, are you referring to the orange block where the pipes come into?
Jason

 

[materthegreater]

No, the valve that controls the thumb should be in front of the oil tank under the cover to the right when you're sitting in the seat. If you open the engine cover and then the side cover, you should be able to watch which valve moves when you move the foot pedal. There is a cable that goes from the pedal to the valve. Same as for the blade and boom swing.
I just had another thought. Is that orange box on the dipper a manual valve or something in case you don't have the attachment on? I'm not real familiar with how aux hydraulics work.

 

[Someotherguy]

I will look at that valve tomorrow. Thank you.
I'm not exactly sure what the orange box does, I think it might have something to do with using a hammer. Looks like there might be some kind of return line on it.
Jason

 

[Someotherguy]

The valve seems to be ok. Doenst seem to be anything wrong with it.

 

[joispoi]

Is there a valve to switch from 2 way function to breaker function? That might explain the high speed one sided symptoms you're having/

 

[d4c24a]

Is there a valve to switch from 2 way function to breaker function? That might explain the high speed one sided symptoms you're having/

might well be under the floor plate

 

[materthegreater]

So the valve moves fully in both directions? I've had a small stone or something similar get stuck under the pedal that keeps it from opening all the way...
Other than that I'm out of ideas

 

[Someotherguy]

I dont know how the breaker function would work. (which way to push the peddel etc).
Ive been going through a service manual but havent seen anything so far.
Ill check tomorrow for a valve.
Thanks for the help guys!

 

[willie59]

I have to admit I know nothing about the Kubota system, but was curious and did a little search. Is that a KX71, or a series machine like KX71-3? If it's a straight KX71, as Mater pointed out, it has a foot pedal that operates a control cable connected to valve spool, I'd look real close if that control cable is moving valve spool fully.

Not sure what the manifold block on side of boom is, and parts pages weren't much help, simply called it a "block", well...duhh. :Banghead

Could you get some more pics at different views of that "block", I'd wager it switches aux circuit from single acting to double acting, but can't say for certain.

 

[Someotherguy]

Thank you willie.
Ill get more pics on tomorrow, and take a good look at the underside of the foot pedal. Its just a KX-71.
I couldnt find anything in my shop manual that helped me, but then again im not a mechanic.

 

[willie59]

No worries Someotherguy. I did find Kubota parts pages online, it shows the KX71 is a cable operated control valve, I'd look real good to see that the cable is moving control valve spool fully.

 

[d4c24a]

in your first picture , that could be the vale to make the circuit double acting , it looks to have a square nut to turn , have you given that a try

 

[Someotherguy]

I looked underneath where the foot pedal attaches to the cable. Everything seems to be operating like it should.
The square nut on the block seems to be just a plug for that hole. I have had it out before and it just leaks out some hydraulic fluid like I would expect.
Tonight I will look at the service manual again and see what I can find.
Thanks guys.
Jason

 

[Someotherguy]

Hi Willie.
Here are some more pics of the block, and the control cable attached to the foot pedal.
Jason

 

[willie59]

Again, I don't know that machine, but I'll wager your problem is caused by that line connected to the side of that junction block on the boom. I know it's going to be difficult to verify this because it's a mini-ex and it's terribly difficult to follow hoses on those things, but you need to see where that hose that's connected to the side of the block goes. It's my guess that hose is used during breaker operation, which doesn't send return oil back through control valve, but returns oil more directly to tank.

If you need to remove machine covers, find where that hose goes. It might go to a manual operated valve or a solenoid operated valve. If you can find that, see if the other connection to that valve goes to tank and no where else. If it does, disconnect that hose connected to side of junction block on boom, and where that hose connects to panel on front of machine, cap those fitting with appropriate caps, and try your thumb. I'll go out on a limb and wager it will work proper now.

 

[Someotherguy]

That hose on the side is a return. It goes to a bank with a few other hoses.
I spoke to a local Kubota mechanic today. He told me that there would be an adjustment I could make on the control valve assembly. He believes that the close pressure is set to high, and the open pressure is set way to low.
Problem is, I dont see where there is any way to adjust the spool section. (evident in the pics?)
I think you are more on track here Willie. Im going to see if I can maybe bypass the block, or disconnect the return and see what happens.

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