hydraulic woes on kubota 4672A backhoe attachment

[travmsns]

Hello I was hoping someone could help. I have a Kubota tractor with a Kubota 4672A backhoe attachment. The hydraulic valve that controls the main boom piston is giving me some problems. When I press the control lever forward, which in turn depresses the valve into the valve block the valve will go into the valve block a little bit and then it feels like it's hanging up, if I press the lever a little harder it will click past that sticking point and depress the valve all the way. The problem is I only have power on the boom/piston up until the sticking point on the valve/lever and even then it feels like I'm not getting full power (it struggles with a bucket full of dirt), then once I'm past the sticking point, I have NO power at all to the boom/piston. So it seems like there's a problem with the hydraulic valve that goes into the valve block, but only the valve that controls the main boom piston. What's involve with fixing this? Thank you!

 

[rswyan]

It ain't broke, the boom valve has a "float" position (RTFM ...... )

When you say "it struggles with a bucket full of dirt" ..... how 'zactly are you determining that ?

That the 'hoe operates slowly ? ..... the tractor engine is bogging down ? ..... valve goes into relief ?

..... ummm ..... how fast are you running the tractor's engine ? (what rpm)

 

[kennyd]

Welcome to TBN

It sounds like a linkage problem to me, there is just not a lot in a spool valve that can go wrong-especially one with out a detented float position.

 

[travmsns]

Thanks for the replies.

When I say it struggles, I mean the backhoe is very slow. I've owned this tractor for 5 years now and this is the first problem I've had with the backhoe. All the rest of the backhoe hydraulic components work fine, the bucket, stabilizer legs, etc. The main boom valve never stuck/hungup mid way in the past and ever since it started doing that, that's when the main boom started to malfunction. All the other control levers and associated valves are smooth and function without problem. But this one, like I said, gets hung up midway when depressing the valve (via the lever) and from that point on it'd dead, and up to that point it's like it's not getting full pressure.

I don't think it's a linkage problem because the valve still has the same amount of travel as the other ones next to it in the valve block and the lever that controls that valve is attached directly so I could see if there was slack or something getting caught up somewhere.

It ain't broke, the boom valve has a "float" position (RTFM ...... )

When you say "it struggles with a bucket full of dirt" ..... how 'zactly are you determining that ?

That the 'hoe operates slowly ? ..... the tractor engine is bogging down ? ..... valve goes into relief ?

..... ummm ..... how fast are you running the tractor's engine ? (what rpm)

 

[rswyan]

When I say it struggles, I mean the backhoe is very slow.

As far as speed is concerned, the PTO pump Kubota supplies with the BH4690B backhoe is capable of a fairly significant amount of flow at high pressure ..... but it will never achieve it - as long as it's running off the tractor's PTO.

IIRC, it is an Eaton pump .... and it has a rated input speed of several thousand RPM .... but since the PTO speed driving it is only 540 rpm ..... it will never reach the flows that it is actually capable of ...... (poor pump selection on Kubota's part)

Comparing the performance of my backhoe with say, a Kubota KX91-3 mini-excavator, the BH4690B is a complete dog ..... even running the tractor's motor fairly fast (2000 rpm) ...... the mini-ex is lighting fast in comparison.

I've owned this tractor for 5 years now and this is the first problem I've had with the backhoe. All the rest of the backhoe hydraulic components work fine, the bucket, stabilizer legs, etc.

Sounds like the valve has loosened up to the point where it will go into the detented float position more easily ......

The main boom valve never stuck/hungup mid way in the past and ever since it started doing that, that's when the main boom started to malfunction.

It took me quite awhile (more than a year) before I "discovered" that the boom circuit on the valve of my BH4690B backhoe had a "float" position .....

If I had fully studied the manual in the first place, rather than just giving it a superficial read when I got it, I would have known this ....

All the other control levers and associated valves are smooth and function without problem.

The boom circuit on that valve has a detented float position - just like the lift circuit on your FEL - if you push the control lever on the FEL control valve straight forward, you will eventually reach a resistance or "stop" ..... if you continue firmly and deliberately to push the control lever forward, the lever will continue past this resistance and the valve will go into "float" position and allow the lift cylinders to "float" up and down ..... providing neither pressure (upforce or downforce) nor resistance ....

But this one, like I said, gets hung up midway when depressing the valve (via the lever) and from that point on it'd dead,

When it goes into the "float" position, it should be "dead" .....

and up to that point it's like it's not getting full pressure. I don't think it's a linkage problem because the valve still has the same amount of travel as the other ones next to it in the valve block and the lever that controls that valve is attached directly so I could see if there was slack or something getting caught up somewhere.

This part is a little puzzling ..... if you are saying that the performance of all other components controlled by the valve are functioning the same as they always have, but the boom performance is slower than it ever has been, then it would seem to indicate a problem with that portion of the valve only .....

Perhaps there is a relief for that section only, which is out of adjustment or otherwise not functioning correctly ...

 

[kennyd]

If rswyan is correct about it having a detented float position, Then I would suspect that the detent body (the thing on the rear end of the spool usually held on with Allen screws) is dry and/or rusted and needs to be removed and greased. A picture of your valve stack will help determine for us what you actually have.

 

[travmsns]

Thanks for all the replies. I'm going to hook up the backhoe shortly and do some testing again. Maybe it was just digging some hard ground and at the same time we realized there was a detented float position for the first time. I will check back in with the details. My dad was using the tractor when it started happening but I didn't operate it myself to feel so maybe I misunderstood what he was saying when he was trying to show me and didn't pay close enough attention to what the boom and lever was doin when I was talking to him. I will go test it myself and find out exactly what's happening. I was just explaining what was described to me and the feel of the lever after I detached it later on. If there really is something wrong after I operate it myself, I'll take some pictures and update with better details.

 

[travmsns]

Thank you guys for the help!!!! After trying it out for myself and not just observing, it looks like all is well and it was a detent'd floating position that he was feeling as part of it. Additionally He said he might have been going easy on it, after he felt the click past the detent thinking it was broken, and him going easy was perceived as a lack of power prior to getting the floating point. So all is well. Thanks and I guess we should've RTFM.

 

[rswyan]

Thank you guys for the help!!!! ......... So all is well.

Good deal :thumbsup:

Thanks and I guess we should've RTFM.

Been there, done that myself ..... too many times to count ...

You're quite welcome - glad to have been of service ....