Kubota mini excavator KX41-2V left track issues

[xenophon.nl]

The left track of my excavator (Kubota KX41-2V) does not have enough power to make a turn.

I replaced the left final drive but that didn't solve the problem.

So I connected an extra set of hoses directly from the control valve left travel section to the drive motor, but no difference.

The 'auxiliary' (for me the thumb) function is on the same pump. When I connect the hoses directly from the auxiliary section to the left drive motor both tracks work fine!

So I concluded the rotary joint, pump, and drive motor are okay.

I tried swapping the spool of the left track with the spool of the right track, but again no difference.

I suspect the left travel section might be broken, but how can I be sure? I could take the entire main control valve out, but that looks like a big job, and I don't see any wearable parts, so would that even be fixable?

 

[ruger1980]

Do you have the WSM or at least a schematic you can post?

 

[xenophon.nl]

Yes I have, I will include in this post.

 

[hagrid]

Yes I have, I will include in this post.

Based upon the attachment I would check the Schwingen, the Schwenken, and both Fahrts.

 

[Henro]

The previous diagram is for the KH 41–2.

This one is for the KH 41–2 V. Not sure if the differences are significant or not. The OP’s is the -2V model.

Sorry for the highlights, but I don’t think they’ll be in the way

edit: I believe there are differences between the North American model and units sent to other countries. Pretty sure the diagram I posted here is for the North American model.

 

[ruger1980]

Did you run hoses from the main control valve to the motor or to the swivel joint? The hoses and swivel are the only thing between the spool and the pump. The travel spool is cable actuated so make certain you do not have an issue there. You could swap left and right travel hoses to see what happens, if hoses will reach.

This is assuming the schematic you attached is the correct one for this machine. A change in series can make a big difference in schematics.

 

[xenophon.nl]

I have a KX41-2V European version. I only have the circuit diagram for KX41-2.

I run hoses from the main control valve directly to the motor. I will include a picture.

I did a test where I disconnected the lever, and I manually pressed the spool (where the spring is). This didn't make a difference. I can also see the lever compresses the spring all the way. So I think the lever is fine.

On the second picture you see the hoses connected to the thumb controls. Driving with the thumb controls and right lever gave full power on both tracks.

 

[Henro]

I have a KX41-2V European version. I only have the circuit diagram for KX41-2.

I run hoses from the main control valve directly to the motor. I will include a picture.

I did a test where I disconnected the lever, and I manually pressed the spool (where the spring is). This didn't make a difference. I can also see the lever compresses the spring all the way. So I think the lever is fine.

On the second picture you see the hoses connected to the thumb controls. Driving with the thumb controls and right lever gave full power on both tracks.

It looks like a lot of the control valves may have pressure relief valves built into them, if I remember correctly.

Perhaps there’s a chance that the control valve for that particular track has a pressure relief valve that is relieving pressure too early? Just a thought I’m not sure if that’s the case or not. It’s been a while since I looked at the hydraulic drawings and I never did look at the drawing for the Version other than the North American version.

 

[ruger1980]

If you bypassed from the MCV to the travel motor and it works OK it is most likely the seals in the center swivel. There are no relief valves in the MCV only the motor so It cannot be that.
I believe you stated that you ran hoses from the auxiliary circuit to the LH travel motor but did you run them from the LH travel spool to the motor directly?

 

[xenophon.nl]

I did swap the main relief valve, A2 with A1 on the picture, with no result.

I have 3 pressure check points, each for a pomp I believe, and I measure around 180-190 bar on all of them, also when using only the left travel.

If you bypassed from the MCV to the travel motor and it works OK it is most likely the seals in the center swivel. There are no relief valves in the MCV only the motor so It cannot be that.
I believe you stated that you ran hoses from the auxiliary circuit to the LH travel motor but did you run them from the LH travel spool to the motor directly?

So when I bypass from LH travel to the travel motor it does not work OK. From auxiliary to the motor is does work OK. That does not proof the center swivel is fine, but does show the problem is also somewhere else. And that is what I would like to isolate.

 

[ruger1980]

I would recommend using the right travel valve to test the left travel circuit. The auxiliary spool is very different so it is not a fair comparison to test with that function.
You are seeing 180-190 bar on all t3 test ports correct? That is a little low but should not cause an issue with 1 weak function. Does the arm function work correctly and do you see the same pressure when using the arm?
Does the travel deviate when tracking or does it just not want to drive when under a heavy load?

 

[xenophon.nl]

I noticed the auxiliary spool is different, it sits right next to the left travel valve, and it is powered by the same pump, so I think that shows the pump is capable, I don't know if it means anything for the main control valve.

I have tested taking out the spools of both travel sections and switching them, but with no difference.

All functions seem to work correctly, although I suspect the swing function (or swivel? the one to move the house around) to also not be on full power.

But the left travel is more obvious: only activating left travel moves a tiny but and then stops under load. Activating both left and right you can move forward but very slowly, If you give full power the right track is much stronger so it steers to the left. When I lift the tracks in the air I can see visibly that the left track moves slower then the right track (in both low and high speed).

 

[GreensvilleJay]

yeesh ,just HOW do you work on those hoses and valves !! Doesn't seem to be very much room !!!

I agree with Ruger, swap the drive hoses right and left for proper testing. Those valves should be identical, both the spools and the 'bodies'. Make sure you label them though !!

If the left track now works 100%, then it's a 'left track valve' issue. Might not be the valve or spool.maybe something 'downstream' is slowing the flow ( return to tank ??)

 

[xenophon.nl]

I checked in the part diagrams and the left travel section and the right travel section are not completely the same. Because I had the idea to take the control valve apart and swap the sections, to maybe proof the left travel section is really broken.

Switching the hoses of left and right travel sections sounds like a good test, but the hoses are too short, so I would have to buy 4 hoses to use as extensions. Except the test would proof something between the travel section and drive motor would potentially be faulty, which I think I already proofed the problem is somewhere else when the left travel section was connected directly to the drive motor, and the problem was still there.

So I am guessing it's something between the pump and (including) the main control valve?

 

[ruger1980]

The only thing that could be wrong with the left travel section is if there were severe leakage by the spool. Either massive scoring on the spool or the bore. Using the auxiliary or what they call the service spool is not a good choice to troubleshooting as the auxiliary spool is fed by both P1 or P2 via the bypass passage and is isolated by 2 check valves.
Is there enough room to swap hose at the center hydraulic swivel, either top or bottom?
I would also recommend measuring and recording cycle times for all functions. This is very useful in diagnosing hydraulic faults.

 

[xenophon.nl]

Ok, I will make it myself easy and order the hoses to do the test. I want to continue investigating this problem and I don't have any other ideas. The main control valve is relatively easy to access compared to the rotary joint. I will post the results as soon as I get the hoses and executed the test.

I never heard of measuring the cycle times. Is that just measuring with a stopwatch how long each function takes to perform? Is there data we can compare the results against?

 

[GreensvilleJay]

I'd order 'whip' or 'extension' hoses. They connect in between your existing hoses and valves. Typically they're about 2-3' long and won't empty your wallet.

 

[xenophon.nl]

I took some time but I finally got to do the test. I switched the hoses between the left and right travel valve. The problem has also switched. This means the left lever is always the weakest, no matter if it is driving the right or left track. I must admit the other side is also not the strongest, but for sure stronger then the problematic side.

Any advice on what to do next?

Video: https://youtube.com/shorts/idX8gUKl7AA

 

[xenophon.nl]

After realising that ruger1980 said the aux port is a combination of both pump 1 and 2, I concluded that it is possible the pump is bad. So I took the gamble and replaced the pump and that fixed it!

 

[lugbolt]

I have nothing to add, but I sure am glad I don't have to deal with those anymore....