Kubota junk. Frustration rant

[aczlan]

I don't think you are following me, perhaps because I have not been very clear. It is not very obvious unless you understand where the relief valve is positioned in the system, and the hydraulic path to get to it. I think some industrial and construction equipment have reliefs beyond the spools, but not the typical compact tractor.

We are talking open center systems, let's start with that. The cylinders are protected from being over pressurized by the pump via the system relief or the relief on the spool valve if it has one and if it is set lower than the main system. So if you had 15,000 lbs in a bucket that was resting flat on the ground (your gold collection) that was only designed to lift 2000 lbs, sure enough when you tried to lift it the oil would pressurize the cylinders to the relief pressure (maybe 2500 psi) and then spill over the relief. No harm done. But once the spool is centered, the oil in the cylinders has no way of getting back through the closed spool to get to the pressure relief. So take that same load of 15,000 lbs of gold (about half a yard) and set it gently in the already raised bucket and do not touch the joystick. Let's pretend we actually have that much weight that would fit in the bucket and let's forget that we would blow tires and break axles and tip and such. So we have our hands off the joystick and have the loader a couple feet in the air so it is not resting on the ground. We gently put our 1/2 yard of gold into the bucket and what happens? The oil is in a conundrum, if that can happen to oil. It can't work it's way back past the spool except by internal leakage....and that is slow. The pressure relief in small tractors is blocked from cylinder pressure when the spool is centered, so it can't find a pressure relief. It may try to leak past the cylinder pistons/seals, but that is slow just like trying to leak past the spool valve. All of the sudden we have a huge, huge amount of pressure in the cylinders and we either blow hoses, blow fittings, explode a cylinder (surely a hose first) or other carnage like bent cylinder rods that allow the load to fall to the ground. If a cylinder is very far extended when it gets a huge pressure spike, then the rod will often bend before a hose blows. If the cylinder is retracted and it it's strongest position, probably a hose will blow.

I hope I made this clearer and not more confusing.....

100% correct.
Here is an animation showing how the inside of a dual action valve works:

(note that the "closed center" part of the title refers to the fact that the work ports (which connect to the cylinders) are closed in neutral unlike a motor spool valve).

Aaron Z

 

[MinnesotaEric]

That's crystal clear to me. And it accurately explains what happened to my Kubota L4400's bucket tip cylinders when I extended them with a tree puller on, pointed down, latched onto a tree. I returned the joystick to neutral and put the tractor in reverse to try to pry the tree out of the ground. When I backed up it simply bent the cylinder rods. As you described, the relief valve was worthless to prevent it.

A way to avoid is to install blow-off valves like we have on snow plows (with the relief going to T), but by the time one does that, they can also buy another ram.

In the diagram above P should be open to T, completing the open hydraulic circuit but it gets the point across.

 

[DavesTractor]

That's crystal clear to me. And it accurately explains what happened to my Kubota L4400's bucket tip cylinders when I extended them with a tree puller on, pointed down, latched onto a tree. I returned the joystick to neutral and put the tractor in reverse to try to pry the tree out of the ground. When I backed up it simply bent the cylinder rods. As you described, the relief valve was worthless to prevent it.

I bent a mini-excavator bucket ram as the cost of tuition to learn this myself. Got the bucket way deep in a hole, extended the cylinder rod entirely to get under a very stubborn root, then pulled up on the main boom and got things bouncing a little for some dynamic root ripping action. Worked fine for a couple of roots and I thought I was so smart. Then I turned the bucket cylinder rod into a candy cane shape....and made the second mistake of trying to pull it back into the cylinder hydraulically. That was a $1200 oops. I wish experience wasn't so costly.

 

[ovrszd]

A way to avoid is to install blow-off valves like we have on snow plows (with the relief going to T), but by the time one does that, they can also buy another ram.

In the diagram above P should be open to T, completing the open hydraulic circuit but it gets the point across.

I'd heard of blow-off valves but never looked into cost. I just taught myself to not "do that".

 

[CDN Farm Boy]

I don't think you are following me, perhaps because I have not been very clear. It is not very obvious unless you understand where the relief valve is positioned in the system, and the hydraulic path to get to it. I think some industrial and construction equipment have reliefs beyond the spools, but not the typical compact tractor.

We are talking open center systems, let's start with that. The cylinders are protected from being over pressurized by the pump via the system relief or the relief on the spool valve if it has one and if it is set lower than the main system. So if you had 15,000 lbs in a bucket that was resting flat on the ground (your gold collection) that was only designed to lift 2000 lbs, sure enough when you tried to lift it the oil would pressurize the cylinders to the relief pressure (maybe 2500 psi) and then spill over the relief. No harm done. But once the spool is centered, the oil in the cylinders has no way of getting back through the closed spool to get to the pressure relief. So take that same load of 15,000 lbs of gold (about half a yard) and set it gently in the already raised bucket and do not touch the joystick. Let's pretend we actually have that much weight that would fit in the bucket and let's forget that we would blow tires and break axles and tip and such. So we have our hands off the joystick and have the loader a couple feet in the air so it is not resting on the ground. We gently put our 1/2 yard of gold into the bucket and what happens? The oil is in a conundrum, if that can happen to oil. It can't work it's way back past the spool except by internal leakage....and that is slow. The pressure relief in small tractors is blocked from cylinder pressure when the spool is centered, so it can't find a pressure relief. It may try to leak past the cylinder pistons/seals, but that is slow just like trying to leak past the spool valve. All of the sudden we have a huge, huge amount of pressure in the cylinders and we either blow hoses, blow fittings, explode a cylinder (surely a hose first) or other carnage like bent cylinder rods that allow the load to fall to the ground. If a cylinder is very far extended when it gets a huge pressure spike, then the rod will often bend before a hose blows. If the cylinder is retracted and it it's strongest position, probably a hose will blow.

I hope I made this clearer and not more confusing.....

Your description is quite clear. Also, it must be noted that for a rod to bend it MUST be in compression, it will never bend when in tension. So working with your example, if a rod were the first to fail, it would be the main lift cylinders NOT the bucket cylinders. All the gold in the world (or concrete steps on forks) will rip the mounts out before bending the rod of a typical tilt cyl. The load would have to be acting on/against the bottom of the bucket/attachment for them to fail.

 

[CDN Farm Boy]

I bent a mini-excavator bucket ram as the cost of tuition to learn this myself. Got the bucket way deep in a hole, extended the cylinder rod entirely to get under a very stubborn root, then pulled up on the main boom and got things bouncing a little for some dynamic root ripping action. Worked fine for a couple of roots and I thought I was so smart. Then I turned the bucket cylinder rod into a candy cane shape....and made the second mistake of trying to pull it back into the cylinder hydraulically. That was a $1200 oops. I wish experience wasn't so costly.

It would have been the bouncing that did it in, not using the other cyl. Expensive lesson. I'm fortunate that this was a lesson I learned along time ago without causing any damage. That being said, I did bend my loader boom itself catching the corner of the bucket on the top of a buried post while plowing snow...I'd have preferred a bent cyl :banghead:

 

[hunter townsen]

CDN Farm Boy. Bending the dipstick cyl. is easy. I watched a guy hook the bucket on a large buried rock then when the cyl. could not move the rock he backed up and tried to force the rock out. After the third ram backwards the rod bent. Anything is possible.

I had a neighbor who completely destroyed a ford tractor in about 400 hrs, you name he broke it , you should have seen his new jeep lol, first week he ripped the flares off of it. Takes all kinds.

 

[Paul Thornton]

DavesTractor, I thought your explanation was very clear and you have done what has happened on here many times, taught me something new. Thank you.

 

[skyhook]

Ok, now I understand, thanks for the explanation.:thumbsup:

 

[DavesTractor]

Your description is quite clear. Also, it must be noted that for a rod to bend it MUST be in compression, it will never bend when in tension. So working with your example, if a rod were the first to fail, it would be the main lift cylinders NOT the bucket cylinders. All the gold in the world (or concrete steps on forks) will rip the mounts out before bending the rod of a typical tilt cyl. The load would have to be acting on/against the bottom of the bucket/attachment for them to fail.

You are correct, that is a point where my example broke down. Thanks for clarifying. A better example may have been one where a guy is trying to push out a tree or something where the rods are in compression....yep, good point. Just like it is hard to bend three-point arms pulling something, but backing up you can sure bend them.

 

[DavesTractor]

It would have been the bouncing that did it in, not using the other cyl. Expensive lesson. I'm fortunate that this was a lesson I learned along time ago without causing any damage. That being said, I did bend my loader boom itself catching the corner of the bucket on the top of a buried post while plowing snow...I'd have preferred a bent cyl :banghead:

Good point again, and in the vast majority of situations you are correct. I have seen a couple of bent bucket rods on backhoes where guys swear they were doing no bouncing, etc. The situation was always where they had the bucket rod fully extended and a load on the tips of the bucket teeth against a root or something that would not budge. A couple of years back, Mahindra began to installed "blow-off" reliefs on that bucket circuit between the bucket cylinder and the spool on the 3720. The 3720 is a beast of a little backhoe. The main boom lift cylinder relief should protect the bucket cylinder in a properly designed system. But you also do not want to make the main boom lift less powerful only to protect that odd situation I described when the bucket rod is most vulnerable. A blow off relief is the best of both worlds. That way the main boom is not dumbed down, it still has a ton of grunt, yet it will not cause damage to another part of the backhoe.

Bent loader boom....bummer. Experience is so expensive. That is the beauty of a forum like this, people can learn from other's mistakes and get free tuition.

 

[hunter townsen]

One thing people need to remember about cylinders , they are designed to push straight, so any binding in the connection points can be detrimental, I.e. bad bushings, lack of grease, corrosion. Any excessive resistance on the mounting points needs to be addressed. I try to keep this in mind as I work also, so when im working my tractor hard if possible I try to adjust my hoe or fel with the force on the cylinders as straight of a push as possible or I try to have them closed as possible
Have a good day
rob

 

[Bing187]

There's some great info here. Thanks Dave, and all, for simplifying some of this stuff. As far as bending rods, I get exactly the point as far as leverage, as when I bent the two on the tilt/ roll function, it was when I was backing up with the forks rolled down, so pistons were all the way extended, and the tractor backing up caused too much pressure and bent them... I don't understand why these machines don't have a relief valve like a plow, as Eric mentioned. I have, since then, tried to never move anything by moving the tractor with a load in a position so it puts pressure either way on the hydraulics.... If I need to pull a stump out of a hole, and can't do it with backhoe, I chain it to 3ph, or the truck.
As to my machine, dropped it off this am. Yesterday I messed with 3ph lever, loader would go up if I pulled partway on lever, stopped if I pulled all the way. Put it on trailer last night. This am, nothing different, loader back to not going up at all. It's a mystery.

 

[aczlan]

As to my machine, dropped it off this am. Yesterday I messed with 3ph lever, loader would go up if I pulled partway on lever, stopped if I pulled all the way. Put it on trailer last night. This am, nothing different, loader back to not going up at all. It's a mystery.

Do you have numbered settings for your 3 point (ie: put it at 5 and it always goes to the same height)? If so, the "three point feedback" rod/lever (which is what stops the 3 point at a given height) may be misadjusted.

Aaron Z

 

[DavesTractor]

There's some great info here. Thanks Dave, and all, for simplifying some of this stuff. As far as bending rods, I get exactly the point as far as leverage, as when I bent the two on the tilt/ roll function, it was when I was backing up with the forks rolled down, so pistons were all the way extended, and the tractor backing up caused too much pressure and bent them... I don't understand why these machines don't have a relief valve like a plow, as Eric mentioned. I have, since then, tried to never move anything by moving the tractor with a load in a position so it puts pressure either way on the hydraulics.... If I need to pull a stump out of a hole, and can't do it with backhoe, I chain it to 3ph, or the truck.
As to my machine, dropped it off this am. Yesterday I messed with 3ph lever, loader would go up if I pulled partway on lever, stopped if I pulled all the way. Put it on trailer last night. This am, nothing different, loader back to not going up at all. It's a mystery.

Once you understand the dynamics of what is happening, you can better know when you can "push" the machine a little over max, and when you should not. Your example of backing up with the forks rolled down is classic, it would be hard to do something much worse on the bucket rams.

Odd that you have had so many loader valve issues. I do not think that is common with Kubota. Do you have extra dealer or user installed hydraulics on it, like top/tilt? I'm just wondering if there is any other factor that might be contributing to these failures. I understand the bent rods, I don't so much understand the failed valves.

As to why the machines don't have blow off reliefs, it is due to cost. As much as we all say we would gladly pay for it, the truth of the matter is that when we are shopping we may not see the value initially, and if the loader/backhoe cost $1000 more due to some more industrial hydraulic circuits, most guys would not see the value.

Just like when we sell a $6000 backhoe attachment and some guy that runs a $150k excavator at work complains that the controls are not as smooth or that it is slow or jerky if he is running all 4 spools at once....we remind him that just the control valve system on his excavator cost more that the entire backhoe attachment. Could a CUT backhoe attachment run pilot controls and a huge pump....sure, but it would be priced about double compared to the competition.

 

[Bing187]

The tractor is stock, with the exception of ATI quick change bucket/ forks. I agree, I think that my experiences with hydraulic issues seem unusual, especially on a machine with such low hours. Fluid and filters have been changed, etc. I'm fairly good about lubing the 3 zillion grease fittings on the loader and backhoe... I'm thinking that when I get machine back, maybe I should figure out a way to flush the whole system, lines, cylinders, the whole shebang. I guess I'll have to see what has failed. I would think that a contaminated system would have parts wearing quicker than they should, not breaking....
The dealer isn't going to start diagnosing till end of next week.... I'm climbing the walls.

 

[ishiboo]

I bent a mini-excavator bucket ram as the cost of tuition to learn this myself. Got the bucket way deep in a hole, extended the cylinder rod entirely to get under a very stubborn root, then pulled up on the main boom and got things bouncing a little for some dynamic root ripping action. Worked fine for a couple of roots and I thought I was so smart. Then I turned the bucket cylinder rod into a candy cane shape....and made the second mistake of trying to pull it back into the cylinder hydraulically. That was a $1200 oops. I wish experience wasn't so costly.

Reminds me of my near tragedy. Was digging up a VERY small tree, and the thumb on a rented hoe got lazy... kept falling down. Being a thumb, it was set up to "give" to the bucket curl anyway, so I pushed it out of the way. Did it again, went to push it back and BOOM... snapped the rod off.

Was dreading the repair, when I went to finish the job with the now disconnected thumb... and found the rod end, nutless, in the hole. Turns out the nut of the rod end in the cylinder had worked its way off, which allowed the cylinder to over-extend. I had already dropped off the cylinder at the dealer, they took care of it on their dime, no questions asked.

If I would have known the nut was loose I would have stopped immediately, I just thought there was a minor valve problem and pushing the thumb back on the relief was no problem.

 

[hunt4570]

I don't think you are following me, perhaps because I have not been very clear. It is not very obvious unless you understand where the relief valve is positioned in the system, and the hydraulic path to get to it. I think some industrial and construction equipment have reliefs beyond the spools, but not the typical compact tractor.

We are talking open center systems, let's start with that. The cylinders are protected from being over pressurized by the pump via the system relief or the relief on the spool valve if it has one and if it is set lower than the main system. So if you had 15,000 lbs in a bucket that was resting flat on the ground (your gold collection) that was only designed to lift 2000 lbs, sure enough when you tried to lift it the oil would pressurize the cylinders to the relief pressure (maybe 2500 psi) and then spill over the relief. No harm done. But once the spool is centered, the oil in the cylinders has no way of getting back through the closed spool to get to the pressure relief. So take that same load of 15,000 lbs of gold (about half a yard) and set it gently in the already raised bucket and do not touch the joystick. Let's pretend we actually have that much weight that would fit in the bucket and let's forget that we would blow tires and break axles and tip and such. So we have our hands off the joystick and have the loader a couple feet in the air so it is not resting on the ground. We gently put our 1/2 yard of gold into the bucket and what happens? The oil is in a conundrum, if that can happen to oil. It can't work it's way back past the spool except by internal leakage....and that is slow. The pressure relief in small tractors is blocked from cylinder pressure when the spool is centered, so it can't find a pressure relief. It may try to leak past the cylinder pistons/seals, but that is slow just like trying to leak past the spool valve. All of the sudden we have a huge, huge amount of pressure in the cylinders and we either blow hoses, blow fittings, explode a cylinder (surely a hose first) or other carnage like bent cylinder rods that allow the load to fall to the ground. If a cylinder is very far extended when it gets a huge pressure spike, then the rod will often bend before a hose blows. If the cylinder is retracted and it it's strongest position, probably a hose will blow.

I hope I made this clearer and not more confusing.....

Nice descriptions, hydraulics and their valving is all a bit of a mystery to me anyway, not real sure why.

BUT does any of it matter anyway? If you have half a yard of gold in your bucket then who cares!:laughing:

 

[Bing187]

Talked to Norfolk power today. According to the shop foreman, female quick connect on "up" side of loader was jamming closed. I swear I switched that fitting with one from tilt/ curl side to check that very thing, but..... He says all lines checked out at male side with pressure gauge, but that one was dead on other side of female fitting... So they replaced it, tried it out in a snowpile, and it's working totally normally.... Smfh.... Lol. I guess $250 in diagnosing and a (guessing) $20 part beats a loader valve. Thanks for all the good advice, and the hydraulic lessons... I definitely have a better understanding of some of it now...
Mike

 

[Garandman]

Bing187 I feel your pain brother......

You won't get any shoulders to cry on with the orange crowd here, ask me how I know?

..