kubota bh77 dipperstick cylinder problem

[DB Pilot]

I got the backhoe back a few days ago. It is working and I was told the "lower relief valve" for the dipper stick was the problem. Have not received the bill yet. When digging all seems to be normal and strong. Only difference I find as that now after sitting for a while the backhoe will drift to the side, while driving around, and can be pushed side to side by hand. After using the backhoe it stays centered and cannot be moved by hand. Before the repair I never had to used the Pin that keeps the BH centered. and never had it drift off center.

Now When starting up cold and driving to a dig site I turn around and the BH is swung to the side. By working the BH with the control lever the drifting stops for the rest of the day. It has only been a couple of days so I'm not sure if that will stop. There must be a reason for Kubota to have that centering pin? Again no need for the pin before. :2cents:

Have a great 4th of July, everybody.

 

[Smokeydog]

Boom lock and center pin lock are for transport or storage. Other brands use them. I need to look at my reliefs if problems persist.

 

[rScotty]

I'm glad that the lower relief valve worked for yours. Replacing one is a minor job so it shouldn't be much of a shop bill. Did you get the old one back? It would be interesting to take it apart and see why it failed. I'll gladly pay the postage.....

On the backhoe drifting side to side, some do that & some do not. On the backhoe on our Kubota M59 I used the pin religiously for the first few hundred hours and them began to ignore it. The swing cylinders held it fine for the next decade without the pin, but now I see it drifting some when I am driving or when it is parked. Maybe an inch a day. So I'm back to using the anti-swing pin again.
My guess is that the swing latch pin is mostly to reduce the shock load on the swing bushings when transporting. You really ought to use it. So should I...

Do not understand when you say it can be pushed from side to side by hand. I probably couldn't push mine to make it swing more than a fraction of an inch with another tractor and a winch...even when it isn't running. You might want to note if it is easy to push in one direction only.
rScotty

 

[DB Pilot]

I regret that I was so happy to get the BH back I completely forgot to ask for the old parts. As to the side to side movement it is in both directions but after just a little use it tightens up so that I cannot move it by hand at all. :confused3: I am able to talk directly to the mechanic who worked on it. So if I get time, I will stop in and mention what is going on and maybe get the parts? I always put the boom hook on but now I think I'll use the anti-swing pin too.

 

[nbryan]

I regret that I was so happy to get the BH back I completely forgot to ask for the old parts. As to the side to side movement it is in both directions but after just a little use it tightens up so that I cannot move it by hand at all. :confused3: I am able to talk directly to the mechanic who worked on it. So if I get time, I will stop in and mention what is going on and maybe get the parts? I always put the boom hook on but now I think I'll use the anti-swing pin too.

I've always used the boom hook and swing pin. Even nudge the boom down against the hook before shutting off the engine. I don't know anything really about the design and tech involved with the hydraulic system, but sense that the system isn't designed to handle a sudden unbalanced load against the cylinders with engine off and no system pressure. A jarring bump on my trailer would exert a sudden big downward force on the boom cylinder if it wasn't clipped in place, no?
With the engine on and pump pressure, it's made for a pounding. No pressure, back-leakage problems?

 

[Smokeydog]

View attachment 662205
My M59 backhoe swing lock was missing so scrap piled this one.

Operating with the backhoe attached on my hilly ground have to often swing the hoe to the side uphill to maintain balance so often can’t lock in place. Using the locks when you can takes lots of stress off the hydraulic system.

There is something funny going on causing these relief valves to fail like they do. Trapped air?, dirt leg or design? While the system is designed to handle working pressures ~3000psi, that can easily be exceeded by forces external. A friend of mine was complaining his backhoe was leaking down faster than when new. Some while operating, a lot when parked. He routinely didn’t use the locks. Low hour, new machine, B26. Took a while to discover he was dragging logs thru Mountain terrain chained to his backhoe bucket. Tried to explain how this puts extreme pressures on the cylinders and and valves beyond what was designed for. The cylinders become pumps with a big lever arm. Not what he wanted to hear. “It’s Kubota’s fault, not the operator. “
High end grapple buckets for the more powerful skidsteers now have pilot check valves to help protect the machine from the cylinder pressure when operating. Manufacturer of the grapple has measured the grapple cylinder pressure 3x higher than machine pump pressure. I can easily see why when grappling and pulling tree limbs. Might be a good idea for tractor grapples too.

With the OP’s help have taken a step closer to figuring out the problem and how to fix it. I need a better understanding how these relief valves are working to understand how they fail.

 

[rScotty]

View attachment 662205
My M59 backhoe swing lock was missing so scrap piled this one.

Operating with the backhoe attached on my hilly ground have to often swing the hoe to the side uphill to maintain balance so often can稚 lock in place. Using the locks when you can takes lots of stress off the hydraulic system.

There is something funny going on causing these relief valves to fail like they do. Trapped air?, dirt leg or design? While the system is designed to handle working pressures ~3000psi, that can easily be exceeded by forces external. A friend of mine was complaining his backhoe was leaking down faster than when new. Some while operating, a lot when parked. He routinely didn稚 use the locks. Low hour, new machine, B26. Took a while to discover he was dragging logs thru Mountain terrain chained to his backhoe bucket. Tried to explain how this puts extreme pressures on the cylinders and and valves beyond what was designed for. The cylinders become pumps with a big lever arm. Not what he wanted to hear. 的t痴 Kubota痴 fault, not the operator.
High end grapple buckets for the more powerful skidsteers now have pilot check valves to help protect the machine from the cylinder pressure when operating. Manufacturer of the grapple has measured the grapple cylinder pressure 3x higher than machine pump pressure. I can easily see why when grappling and pulling tree limbs. Might be a good idea for tractor grapples too.

With the OP痴 help have taken a step closer to figuring out the problem and how to fix it. I need a better understanding how these relief valves are working to understand how they fail.

Well said, and I like it. The point about pressure spikes is real and something that every operator should be aware of. I think that most operators are aware of the dangers from back pressure spikes. Maybe a few aren't....like chaining a log to a bucket...sheesh!

But aside from things like that, the backhoe failures that Kubota is seeing could sure be the relief valve..... or it could be someting else in the system related to the valve - for example something like an air bubble or piece of crud that gets "reset" when we remove and replace the relief valve. But looking at some failed relief valves with a gimlet eye might be a good idea. It couldn't hurt.

If I can divert for a moment, there was a time 50 years or so ago when industry was very open to ideas from independent mechanics as well as from clubs like here on TBN. At that time, industrial designers actively sought outside opinions and there were even open competitions for anyone wanting to design better gadgets. Mechanical innovation flourished.

Then came the legal rulings and lawsuits of the 1970/80s. The lawsuits had the effect of making engineers and designers reluctant to admit that anything they designed could possibly have a flaw or be improved. In less than a decade, industrial engineers who wanted to keep working were required to sign a lot of legal paperwork making sure that they would never discuss design with anyone outside the company. I did that with every job I took. Everyone did. Today that philosophy is even more common and has directly led to a rash of disasters in automotive, aviation, aerospace and structural design.

Frankly, mechanical design has been stagnent for many decades now; tractors from the late 1990s look and act a whole lot like the new ones today. There is even an argument that older is better. During this period electrical design has made huge gains.

Eventually the public will force change to happen.... we always do. I wonder what will cause change to happen this next time?

Back to relief valves....being ignored by industry has the advantage that as amateurs we can discuss them without any constraints. Another thing in favor of the relief valve idea is the weight of evidence... When the DB's Kubota mechanic was presented with that BH77 problem, he tried the easy stuff first - and that's good practice and it kinda worked. But then when the easy stuff didn't entirely fix things he re-considered the symptoms and went straight to the relief valve as being most probable. I did the same when my M59 failed to swing - which is why a couple of spare & unused relief valves are still sitting on my tractor parts shelf in the barn. Like so many Kubota backhoes we hear about on TBN, mine "fixed itself" before the relief valves arrived.

Bottom line is that there may be an opportunity here for someone. A very simple system is involved. Parts are cheap, and there are even other similar systems to look at that don't have that same problem.
rScotty

 

[Smokeydog]

First I’ll try the mystic engineering approach. Buy new relief valves and store them in the barn to intimidate the backhoe ;-) Don’t understand how that works but have observed this phenomena with other equipment.

Have been fortunate to work in the footsteps of many great engineers and scientists. Agreed things are much different now. The more we learn the more we realize what we don’t know.

 

[crazyal]

You may have some air in the swing cylinders. Try cycling it side to side a number of times to try and purge as much air from it as possible.

 

[DB Pilot]

Thanks to all for the great info and their experiences with BH's. :thumbsup: purging air out of the cylinder feels like what may be going on. Main thing is I'm back in business hopefully for a long time. I will always use the anti-sway pin during transport now. :laughing: