Backhoe Sanity Check

[caspar3259]

I've had some problems with my Kubota BH77 backhoe on my L3540. The dealer has fixed it twice and I'm still not sure it's 100% working as designed. I was hoping some of you could offer your comments to help me determine if my expectations are wrong or if the BH still has a problem.

All of the problems seem to revolve around the dipperstick cylinder. Here are the symptoms I notice now (after the fixes) that don't seem right to me:

>>> Dipperstick cylinder retracts (extending the dipperstick) faster than it extends. I would expect the cylinders to move the same speed in & out when there is no load. Maybe I'm wrong? The bucket also seems to curl a little slower than it dumps, but I have had no problems with the bucket.

>>> Curling the bucket against a stump will compress the dipperstick cylinder. When I dump the bucket and raise the boom, the dipperstick will drop quickly and bounce due to the "slack". I expect the dipperstick cylinder to stay in one place even under load.

Do you have any suggestions for some "tests" I could try to see if it's functioning right? I would love to be able to try someone else's BH77 that is known to be working, but I don't know of anyone in the area.

thanks,

-Jeff

 

[N8ghz]

I've had some problems with my Kubota BH77 backhoe on my L3540. The dealer has fixed it twice and I'm still not sure it's 100% working as designed. I was hoping some of you could offer your comments to help me determine if my expectations are wrong or if the BH still has a problem.

All of the problems seem to revolve around the dipperstick cylinder. Here are the symptoms I notice now (after the fixes) that don't seem right to me:

>>> Dipperstick cylinder retracts (extending the dipperstick) faster than it extends. I would expect the cylinders to move the same speed in & out when there is no load. Maybe I'm wrong? The bucket also seems to curl a little slower than it dumps, but I have had no problems with the bucket.

>>> Curling the bucket against a stump will compress the dipperstick cylinder. When I dump the bucket and raise the boom, the dipperstick will drop quickly and bounce due to the "slack". I expect the dipperstick cylinder to stay in one place even under load.

Do you have any suggestions for some "tests" I could try to see if it's functioning right? I would love to be able to try someone else's BH77 that is known to be working, but I don't know of anyone in the area.

thanks,

-Jeff

My question to you would be, what did the dealer fix? Was it these symptoms or something else?

On the line that I highlighted, this seems to be correct, as the most power would be setup when digging toward the tractor, not when pushing on a stump (dipper out or bucket out). The speeds on the power stroke (cylinder extending) would be slower, as more oil is required due to absence of the rod on the 'cap' end. Retracting would be faster because the rod-end requires less oil (again, due to the rod diameter), given the same GPM's the retract is faster than extending due to these fluid requirements. The same applies to the bucket cylinder, or any cylinder for that matter.

I do not know if Kubota has any flow-controls in the circuits, and if they did, speeds could be balanced in spite of what I just said. I doubt if they went to the expense of adding such control valves?

 

[caspar3259]

My question to you would be, what did the dealer fix? Was it these symptoms or something else?

The first problem was the dipperstick would sometimes slowly droop even under its own weight. It would do this for a minute or two and then stop and act normal (i.e. hold its position). After 30-40 minutes of using the BH, the dipperstick just about quit extending altogether. At idle it could not even lift itself with no load. The dealer said the problem was "some assembly gunk in the relief valve".

The second problem was the dipper stick would retract much slower than it would extend. For example, it took about 6-7 seconds for it to extend and almost 20 seconds to retract (dig). It also had very little power when retracting (digging) and would stall in loose dirt. The dealer came up and I showed him. He even tried it himself and agreed it was not digging like it should. The fix this time was "replaced one of the valves". I suspect this was a control valve and not a relief valve, but I don't know.

thanks,

-Jeff
(aka N6DZR ... there are a few hams on this forum :thumbsup

 

[N8ghz]

Well a '73' to you then.

 

[DemcoEd]

I am guessing you still have air in the system. Did the dealer have the cylinder apart? I would try extending the cylinder and hold the lever for 10-15 seconds. Then retract the cylinder and again hold the lever for 10-15 seconds. You may need to do this several times and you may need to do it on all your cylinders because the air that is in the system from the cylinder being apart could now have moved through the system into the other cylinders. Good luck

 

[bindian]

I am guessing you still have air in the system. Did the dealer have the cylinder apart? I would try extending the cylinder and hold the lever for 10-15 seconds. Then retract the cylinder and again hold the lever for 10-15 seconds. You may need to do this several times and you may need to do it on all your cylinders because the air that is in the system from the cylinder being apart could now have moved through the system into the other cylinders. Good luck

Definitely air in the system.
hugs, Brandi

 

[J_J]

Air in a cyl is usually expelled with a couple of cycles of the cyl. If it keeps getting air in the cyl, then it is sucking air via the seal at the rod end, or air is being sucked in at the input to the hyd pump .

Other reasons for the cyl to move, is that the piston seals are leaking, or the spools are worn.

Another reason might be the work port relief may have some debris in the valve.

I would highly recommend a 3000 psi hyd gage in the hyd system to monitor and trouble shoot the hyd hyd system. With the engine running, looking at the hyd gage will tell you if you have pressure and how much.

A more powerful cyl can and will work against another cyl if the mechanical hook up is just so, or the cyl are different sizes. For instance, a bucket cyl can work against a thumb cyl and push the rod back in.

With a valve using a P B port, any expelled air goes out the out port directly to tank.

If the valve only has an IN and OUT port, then any air expelled will be passed downstream to the next valve.

I have a Case BH, and there are restrictors for certain functions, so certain functions may be restricted as far as speed.

A retracting cyl is always faster, and has less power than an extending cyl with no restrictors in the circuit.

 

[k0ua]

-Jeff
(aka N6DZR ... there are a few hams on this forum

Actually there are lot of hams on this forum! not all are posting callsigns, but they are here all the same. There was a thread about a year ago, asking how many were hams, and they came out of the woodwork.

73
de K0UA

 

[caspar3259]

Thanks for the replies. I will try the procedure to purge the air.

Will I hear or feel anything if air is being purged? Or is it just "it will work better when you're done" kind of thing?

If I need to purge them in sequence, how would I know and how do I know what that sequence is?

This newbie appreciates all your help!

-Jeff

 

[Gizmo2]

I have a Case BH, and there are restrictors for certain functions, so certain functions may be restricted as far as speed.

A retracting cyl is always faster, and has less power than an extending cyl with no restrictors in the circuit.

JD uses/has used restrictors in some of their attachments also.

 

[J_J]

You will not hear anything.

When the relief goes off for each cyl as you extend or retract, , you know the relief pressure has been reached. The BH movements should be constant with no slack.

The cyl action will feel spongy, until the air is out. As you add fluid to the cyl, air is expelled. If air continues to get in the cyl, you need to look further for the cause.

 

[J_J]

caspar3259,

Do you have a FEL on your tractor? Is so, does the FEL cyl act the same?

What I am thinking, is that it would be unusual for all cyl on the BH to be giving trouble. If all cyl are acting up, then I believe the air is coming from the tractor hyd pump via a suction hose.

Cyl can suck in air from the rod seals of worn or well used cyl over time, and will cause some of those things you observed.

With good cyl, and a good valve, the BH should have all the applied power manufactured in to it. It should dig with a certain force and with no slack or floppiness, and lock in place and hold when the levers are released.

It might have restrictors, maybe not. The relief on the BH should be set equal toor below the PRV on the FEL.

A hyd gage should be installed.

 

[caspar3259]

J.J. - thanks for all the info. I have a lot to learn about hydraulics.

Yes I have a FEL and it has been working fine.

The only cylinder on the backhoe that has given me trouble is the dipperstick.

I don't *think* the cylinders feel spongy. When I move the dipperstick and let go of the lever it comes to a quick stop and holds there.

I'm starting to think it is working as designed, but I'll go through the "purge the air" procedure to see if it makes any difference. If anything still seems odd, maybe I can get some video of what I am seeing so you can see what I see...

-Jeff

 

[caspar3259]

Update: I tried the procedure to purge air from the dipperstick cylinder. Afterwards I did not notice any difference.

I'm coming to the conclusion that it's working normally. I think what's happening is the dipperstick cylinder is the "weak link" in the system and can be overpowered by the bucket or boom cylinder. I would guess that the relief valve has a lower PSI threshold than the others, so pressure from the other cylinders can cause the dipperstick cylinder to compress/retract under pressure. When this happens the rod end of the cylinder does not draw in enough fluid, so there is some "slack".

Maybe this is a problem as the boom and bucket cannot exert full force if the dipperstick is moving too easily.

 

[J_J]

Does your BH have work port reliefs? Check them out with a gage. You can put the gage on each cyl and check the pressure and relief it the valve has them.