BH75 Piston broke, twice! Design problem??

Volnavy · Apr 9, 2005

I jost bought a L3400 HST with FEL and BH. I now have <20 hours on it and probably only 2 on the BH. I dug out two stumps about three weeks ago, then started on a 4' deep ditch. My father-in-law got about 15 feet of it done one day but it was too muddy and we waited until it dried out.

About 15 minutes into it, the dipperstick would not extend completely. I got out looked at it and noticed the piston was bent. We pulled it all in to go home and it snapped. Kubota got a new one in the next day and I put it on. It rained again so today was the first day I got back at it. About 20 minutes into it it would not extend, and I noticed it was bent again.

This is a new design but I am really suprised this would happen. Has anyone else had the problem? I'm not sure what is causing it. I'm just digging a ditch in 2 foot topsoil on 2 foot of clay. It must happen when I am pulling in, because that would put it under compression, which is how it would have to fail. I would also think it would have to happen when it is nearly alll the way in because that would make it extended the most.

Anyway, I'll call the dealer on Monday. What can they do for me? Keep giving me new cylinders? Would they consider a larger cylinder or would that just over stress another component? I'm starting to think "lemon" and do not want to go to a 3pt BH.

Maybe they should just trade me our a larger machine /forums/images/graemlins/wink.gif

tractorman · Apr 9, 2005

I have had to replace cylinders for BH90 owners due to bending and breaking. Someone at Kubota needs to kick the chief backhoe cylinder designer in the $@#%(@ !

Henro · Apr 9, 2005

Maybe I should reduce my lust level for the BH75... /forums/images/graemlins/shocked.gif

I can report that I have A LOT of hard hours on my BL4690A 3PH hoe, trouble free except for one hose failure...lots of digging, stump pulling, etc.

Curious why the cylinder would bend...seems like it two possiblities would be either defective run of cylinders (weak rods) or some kind of binding that causes the cylinder to feel a bending moment rather than a direct push, as it is extending.

Please keep us updated! Be sure to stress you were not abusing the hoe when the problem occured. Sorry to hear of your troubles...

tinytractors · Apr 9, 2005

I think that Ramon49 would love this thread... /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Pete.

PondFish · Apr 9, 2005

Anyway, I'll call the dealer on Monday. What can they do for me? Keep giving me new cylinders? Would they consider a larger cylinder or would that just over stress another component? I'm starting to think "lemon" and do not want to go to a 3pt BH. 

Ouch... I'm new to all this but this concerns me. I'm about to get a B3030 with the BH75.

Sorry for the bonehead questions but.. . From what I could tell from the B3030 it was connected via a 4pt quick connect to the subframe. Does the L series require a different subframe for the BH75? I thought the BH90 was the BH matched for the L series?

Are there running problems with the BH75s?

Thanks

AntrimMan · Apr 10, 2005

Volnavy,
Please beg or borrow a camera and post a close-up photo of the failure area and another, zoomed out a bit, of the hoe, inquiring minds want to know where this is happening.

Tinytractors,
if you would please, what is the approximate vintage of the BH90's you have replaced cylinders on?
Do you have any photo's to post?

Thanks,
Martin

AntrimMan · Apr 10, 2005

OOPS, the TINYTRACTORS question is aimed at TRACTORMAN,
sorry, my fault, won't happen again.
Martin

JerryG · Apr 10, 2005

I don't know what your digging style is, but the closer you dig to the unit, the higher the chance of bending a cylinder. I have seen many that have bent cylinder that way.

tractorman · Apr 10, 2005

Unfortunately, the broken and bent cylinders are long gone so I can't post photo's. I can tell you that they were for backhoes sold in 2003. Kubota has since updated the bucket curl cylinder rod with a replacement rod 10 mm larger in diameter. Hopefully that is enough to remedy the situation.

Volnavy · Apr 10, 2005

I'll post pictures tonight.

Volnavy · Apr 10, 2005

Here is the first picture.

Volnavy · Apr 10, 2005

Here is picture number two. I wish I had the initial piston that broke, the piston rod snapped, but it first looked like this: bowed into the arm.

Henro · Apr 10, 2005

I don't know what your digging style is, but the closer you dig to the unit, the higher the chance of bending a cylinder. 

Jerry,

Why would that be?

It just seems to me that the beauty of hydrauilcs (if properly designed) would be that the cylinder would just reach the end of its stroke and stall there...or push until it was unable to overcome whatever resistance was oposing its movement, and stall there...Without anything being damaged, and without the cylinder damaging itself.

Personally, I would not want a hydraulic implement that would self distruct during its normal range of operation. Which is what push and pull would seem to be to me. Now side thrusts on a small backhoe is a different story, but I don't think we are talking about abuse here in this thread.

Are there some backhoes out there that do suffer damage to cylinders when operated within the design limits? I sure would not want one of those!

JerryG · Apr 10, 2005

Why would that be? 
That is a good question and I have tried to figure it out several times over the years. But I have yet to formulate a good reason. I know that I have seen many BHs with bent cylinders, just like this one and almost all of them have done so while digging close to the machine, while trying to get the last little bit possible.

kubotabilly · Apr 10, 2005

Henro,
I agree with you. It should not matter if your digging 6 ft. from the tractor or trying to take that last scoop as close to the tractor as possible. I do it all the time with my Woods BH. There has to be a design flaw there somewhere.

Volnavy, get it to the dealer for a good going over. Get Kubota involved.

Bill

plants4u · Apr 11, 2005

Volnavy,

Sorry to hear about the equipment problem. I have the same backhoe as you and your situation concerns me. Since I read your post i did go out and do some extra hard dipperstick digging just to see what may happen. I have not been able to accomplish the same. I wonder if it is possible that the dipperstick or pivot pin bushings are binding? My only issue has been breaking bucket teeth, but my unit has performed well for me. Hope your situation is resolved promptly, let us know.

Clem

Volnavy · Apr 11, 2005

I have had no teeth break and really have not been pushing it at all. WHen I put the new cylinder on I greased all the fittings very well so I hope there is no binding, however the dealer did use the same busing on the piston end, the lower end has none. I'll call them today and keep this thread updated with what I hear. It is good to know someone else has a BH 75 that is working properly.

bugstruck · Apr 11, 2005

Henro, If someone were driving the tractor while dragging logs with the BH bucket, or something like that, I may understand it. I've done that on rare occasion with lighter trees and used mine as a hammer against a stubborn tree this past weekend but I had my dipperstick out (rod in). Maybe I'll ease up on that a little. I've run heavier equipment and never seen a rod bend like that. I'm sure it's happened though.

Seems to be a weak link on some of the Kubota hoes. The reason they are bending when digging in close is probably because thats when the rod is most extended, in compression, and most vulnerable. Per your comments, you shouldn't be able to bend a cylinder like that in any sensible digging operation. Looks like the curl cylinder is beefed up on the newer BH 90 according to the another post. I think that's what I have on my Dec 04 BH. However, I believe it's the dipperstick cylinder issue I've seen the most posts on.
/forums/images/graemlins/confused.gif

Darren · Apr 11, 2005

The rod has to be extended to get bent like that. As you said, that happens when the operator is working close to the machine. When the boom is adjusted so that the minimum amount of rod is exposed, it can withstand more force.

Think of it as a short beam as compared to a long beam. With the same load on both beams (as long as they're the same cross section) the long beam will show more deflection. The cylinder and rod is actually designed as a column but that's just a vertical end-loaded beam in a sense. Once you exceed the elastic limit of the steel, the deflection is permanent. In other words, it's bent for good.

Kubota obviously short-changed the design. Whoever did the design didn't realize the pressure relief valve would allow enough force to bend the rod when it was extended.

Volnavy · Apr 11, 2005

My BH manual shows a picture of someone pulling something with the BH and has a big circle and X over it. In other words that is a "no no".

Kubota is going to pick it up tomorrow and work on it. They said that the stops may not be adjusted correctly. Stops? I thought it stopped when it ran out of travel. Oh well, maybe I'll learn something. He also mentioned something about reducing the power. That worries me, I don't need it any weaker. I guess I could check the lift capacity when I get it back if I had weights that big. Can they really reduce the hydraulic pressure. This one is not PTO powered, it runs off the tractor hydraulics.

They also have a recall on the PTO so will fix that too.

I really wish I could finish digging my ditch. But it is supposed to rain the next three days, so maybe it'll be done by the time it dries out.