L3901 Loader Failure

[AllenBC]

MY L525 loader acted squirrely from time to time in the past, but it would eventually act right. No more. The problem at first was the loader arms were slow lowering and sometimes not lowering but then after a few minutes it would work OK. Slowly it got worse and now the only way to lower is the float function - trying the regular way now actually raises the bucket! Raising the arms the ordinary way now is jerky, but I can eventually raise the bucket. Switching loader arm and bucket quick connects moves the problem to the curl/dump function and the loader works fine. That means the hoses and cylinders are OK and nothing is blocking the quick connects. Hoping a spool valve rebuild would be the solution, I had it looked at by a mobile mechanic and also by a dedicated hydraulics shop. Both removed the spools and found both the spools and everything that can be measured in the monoblock were well within specs. No scratches were found and pressure testing showed no leaks. Their only suggestion is a birth defect: a crack in the monoblock that has gotten worse over the years to the point the valve has totally failed. At this point I am planning to bite the bullet and spend $1080 for a new spool valve unless somebody has a better idea. Anybody even ever hear of such a failure? If cracked monoblocks are known to occur, that will make me feel better about ordering a new one. One final question: Why does Kubota use a two-spool monoblock instead of stacking two single spools?

 

[TheOldHokie]

MY L525 loader acted squirrely from time to time in the past, but it would eventually act right. No more. The problem at first was the loader arms were slow lowering and sometimes not lowering but then after a few minutes it would work OK. Slowly it got worse and now the only way to lower is the float function - trying the regular way now actually raises the bucket! Raising the arms the ordinary way now is jerky, but I can eventually raise the bucket. Switching loader arm and bucket quick connects moves the problem to the curl/dump function and the loader works fine. That means the hoses and cylinders are OK and nothing is blocking the quick connects. Hoping a spool valve rebuild would be the solution, I had it looked at by a mobile mechanic and also by a dedicated hydraulics shop. Both removed the spools and found both the spools and everything that can be measured in the monoblock were well within specs. No scratches were found and pressure testing showed no leaks. Their only suggestion is a birth defect: a crack in the monoblock that has gotten worse over the years to the point the valve has totally failed. At this point I am planning to bite the bullet and spend $1080 for a new spool valve unless somebody has a better idea. Anybody even ever hear of such a failure? If cracked monoblocks are known to occur, that will make me feel better about ordering a new one. One final question: Why does Kubota use a two-spool monoblock instead of stacking two single spools?

Dont spend another penny!!!

This problem gets reported all the time and your control valve is fine but your quick couplers may not be.

First thing to check is the 3pt lift. Lower the 3pt to tje ground and see if the loader starts workimg.

Do you have a third function, remotes, or a backhoe on the nachine?

Dan

 

[AllenBC]

Thanks for your response. I have read about the common causes for this problem but think I eliminated them.

Lowered the 3-point but the problem remains. I do have a 3rd function valve but disconnecting it from the spool valve power beyond but doesn't help. I also have a back hoe and haven't done anything to test whether it is causing the problem - it never has in the past.

I swapped the FEL quick connects for loader arm & bucket. The arms work fine with bucket lines connected to the arm cylinders but then the curl/dump doesn't work - I would think that eliminates the quick connects, the hoses and the cylinders.

I don't want to spring for a new spool valve but don't see an option - but please tell me again I'm wrong.

 

[Runs With Scissors]

Welcome Allen,

I do not know anything about your hydraulic skill level, but I do know that Dan it at the very top of the food chain.

Listen to him, and do exactly as he says, he is a true "Guru".

 

[TheOldHokie]

Thanks for your response. I have read about the common causes for this problem but think I eliminated them.

Lowered the 3-point but the problem remains. I do have a 3rd function valve but disconnecting it from the spool valve power beyond but doesn't help. I also have a back hoe and haven't done anything to test whether it is causing the problem - it never has in the past.

I swapped the FEL quick connects for loader arm & bucket. The arms work fine with bucket lines connected to the arm cylinders but then the curl/dump doesn't work - I would think that eliminates the quick connects, the hoses and the cylinders.

I don't want to spring for a new spool valve but don't see an option - but please tell me again I'm wrong.

You swapped tje female halves of the couplers. The male halves stayed where they were. If one or both of them is not opening you will get your symptoms exactly.

Dan

 

[AllenBC]

One more thing. Against the possibility that the male quick connects on the loader arm side of the spool valve were causing the trouble, I swapped them for the same parts on the bucket side. The problem remained with the loader arm side of the spool valve.

 

[AllenBC]

I have read enough of Dan's posts to value his advice a lot. In fact, I posted hoping he would answer. He picked up quick on the male side of the quick connects - I forgot to include swapping them in my first post.

 

[TheOldHokie]

I have read enough of Dan's posts to value his advice a lot. In fact, I posted hoping he would answer. He picked up quick on the male side of the quick connects - I forgot to include swapping them in my first post.

Exceellent. That would have neen rhe next step. That points to a problem in the downstream power beyond circuit. First potential problem is the 3rd function spool is stuck. Can you or have you bypassed it? If not dont put a lot of effort into it. There are other things to try.

Dan

 

[AllenBC]

My 3rd function is by W R Long so it has solenoids and not a spool valve (wish it did have a spool valve because that would make it easier to control the angle of my snowplow). Anyway, I have it unconnected to the power beyond so it can't be an issue. The only 3rd function part connected is the return to tank and that's totally separate from the loader valve.

 

[TheOldHokie]

My 3rd function is by W R Long so it has solenoids and not a spool valve (wish it did have a spool valve because that would make it easier to control the angle of my snowplow). Anyway, I have it unconnected to the power beyond so it can't be an issue. The only 3rd function part connected is the return to tank and that's totally separate from the loader valve.

The 3rd function has no return to tank. It returns to the power beyond circuit which is why its a concern.

If the spool is not in neutral it will block the power beyond circuit which will block the boom spool on the loader. Thats whybwe need to look at all of the valves downstream of the loader.

Dan

 

[AllenBC]

Here is a hydraulic flow diagram from WR Long that matches my tractor configuration.

It doesn't show a return to the loader valve and I don't have a connection between the 3rd function and the loader valve other than the P hose.

The T hose from the 3rd func heads back toward the backhoe although I haven't traced it completely to the backhoe and it raining now so I don't want to but I will later.

I may be wrong, but with the 3rd func completely separated from the loader valve I don't see how it can affect loader valve function.

 

[TheOldHokie]

Here is a hydraulic flow diagram from WR Long that matches my tractor configuration.

It doesn't show a return to the loader valve and I don't have a connection between the 3rd function and the loader valve other than the P hose.

The T hose from the 3rd func heads back toward the backhoe although I haven't traced it completely to the backhoe and it raining now so I don't want to but I will later.

I may be wrong, but with the 3rd func completely separated from the loader valve I don't see how it can affect loader valve function.

Normal plumbing is loader power beyond goes to P on third function

T on third function is actually power beyond for backhoe and goes to P on backhoe valve.

T on bsckhoe valve goes to P on 3pt valve - upper left port on hydraulic outlet block

3pt valve is locked in full down position which allows it to return to tank

So we need to know exactly what you have hooked up now.

Dan

 

[AllenBC]

You are onto something. I traced the T line to the backhoe so I know that's where it goes. There are only 2 hoses for the backhoe so the 3rd func T line can't just be going to a tank connection in the backhoe because that would require 3 hoses to the backhoe. Did you say something about a power beyond circuit that the 3rd func is a part of?

For fun and giggles I cranked the tractor to be sure the backhoe is still running - it isn't. Tomorrow I will reconnect the 3rd func P line to the loader valve and see what happens. Some of the diagnostics I have done have been with the 3rd func P line capped so I will repeat them. While the loader arm function is still awol, curl/dump works fine even with the 3rd func P line capped on loader valve and 3rd func hose.

Here's one more bit of info I withheld because I didn't think it mattered. My 3rd func was added so I could control a snow plow. With the 3rd func having solenoids that are either full on or full off, changing the snow plow angle tended to go bang left or bang right. I slowed that down by putting a restrictor in the A line going out of the 3rd func to the plow. Even though that restrictor valve was supposed to be high quality, it has been squirrely. I'm taking it out of the line in the morning with the wild hope that will make a difference. Not having snow for awhile now the plow has not been connected so I wouldn't know if that valve shut itself. Before knowing the 3rd func was connected to the backhoe I didn't see how what happened to it could interfere with loader function.

For the snow plow, it probably would have been better to just have a diverter valve and not a full 3rd function. That way the loader spool would be able to change the angle softly. I may add a diverter valve if it ever snows again. I'm 50 miles north of NYC and we had just one significant snow last winter and only two the winter before.

Allen

 

[TheOldHokie]

You are onto something. I traced the T line to the backhoe so I know that's where it goes. There are only 2 hoses for the backhoe so the 3rd func T line can't just be going to a tank connection in the backhoe because that would require 3 hoses to the backhoe. Did you say something about a power beyond circuit that the 3rd func is a part of?

For fun and giggles I cranked the tractor to be sure the backhoe is still running - it isn't. Tomorrow I will reconnect the 3rd func P line to the loader valve and see what happens. Some of the diagnostics I have done have been with the 3rd func P line capped so I will repeat them. While the loader arm function is still awol, curl/dump works fine even with the 3rd func P line capped on loader valve and 3rd func hose.

Here's one more bit of info I withheld because I didn't think it mattered. My 3rd func was added so I could control a snow plow. With the 3rd func having solenoids that are either full on or full off, changing the snow plow angle tended to go bang left or bang right. I slowed that down by putting a restrictor in the A line going out of the 3rd func to the plow. Even though that restrictor valve was supposed to be high quality, it has been squirrely. I'm taking it out of the line in the morning with the wild hope that will make a difference. Not having snow for awhile now the plow has not been connected so I wouldn't know if that valve shut itself. Before knowing the 3rd func was connected to the backhoe I didn't see how what happened to it could interfere with loader function.

For the snow plow, it probably would have been better to just have a diverter valve and not a full 3rd function. That way the loader spool would be able to change the angle softly. I may add a diverter valve if it ever snows again. I'm 50 miles north of NYC and we had just one significant snow last winter and only two the winter before.

Allen

I am "on to something" because I have seen this movie many times. I also own an L3901 with LA525 loader and know the plumbing layout well.

The circuit I described is the power beyond (neutral) circuit and all of those valves are psrt of the daisy chain. You cannot simply disconnect them.

We can diagnose the problem by following and verifying the power beyond flow. Just that simple but I have to know what is actually connected and where.

If you want a manual valve for the snow plow simply add one to the chain rather than screw with a diverter.

Dan

 

[Russell King]

You are putting a lot of words into the thread that don’t answer the question of exactly how it is currently hooked up.

Could you make a sketch and take a picture of that and post it? That would make it plain how it is or was hooked up, since you also seem to be making changes fairly quickly.

Just slow down and think of it as flow through one hose to another hose with valves that only divert the flow when they are activated.

The (potential) pressure from the pump should be able to get into each valve (P) and then out of that valve (PB or sometimes T) and go to the next valve. If you are capping of that flow the pump can deadhead unless it has some pressure relief in place. You can see that in your diagram you posted above.

I think you can simplify the system to eliminate anything except the loader and 3PH but you don’t need to if you know it worked in the past when arranged in exactly the same manner as it is now.

And are you saying that you have moved four complete quick couplers (eight pieces) around on the loader and the problem did not follow the sets? I am unclear on that. I know you moved male connectors and female connectors around but not 100% sure what you did so perhaps post pictures of what you moved around. Most of these problems seem to be solved by replacing a coupler that is defective is why I am asking you about these again.

 

[TheOldHokie]

You are putting a lot of words into the thread that don’t answer the question of exactly how it is currently hooked up.

Could you make a sketch and take a picture of that and post it? That would make it plain how it is or was hooked up, since you also seem to be making changes fairly quickly.

Just slow down and think of it as flow through one hose to another hose with valves that only divert the flow when they are activated.

The (potential) pressure from the pump should be able to get into each valve (P) and then out of that valve (PB or sometimes T) and go to the next valve. If you are capping of that flow the pump can deadhead unless it has some pressure relief in place. You can see that in your diagram you posted above.

I think you can simplify the system to eliminate anything except the loader and 3PH but you don’t need to if you know it worked in the past when arranged in exactly the same manner as it is now.

And are you saying that you have moved four complete quick couplers (eight pieces) around on the loader and the problem did not follow the sets? I am unclear on that. I know you moved male connectors and female connectors around but not 100% sure what you did so perhaps post pictures of what you moved around. Most of these problems seem to be solved by replacing a coupler that is defective is why I am asking you about these again.

Lets keep it simple. Plenty of time for explaining the circuit(s) after we find the fault.

On that tractor and with that 3rd function we can completely bypass the third function and backhoe right at the hydraulic outlet. If the loader works like that we know the couplers are good and we can start on the other components. If it does not work we can revist the couplers.

Baby steps....

Dan

 

[TheOldHokie]

Some of the diagnostics I have done have been with the 3rd func P line capped so I will repeat them. While the loader arm function is still awol, curl/dump works fine even with the 3rd func P line capped on loader valve and 3rd func hose.

Allen

I missed that the first time I read your response.

You cannot deadend the power beyond circuit like that. It over pressures the system, stresses the pump, and will cause the exact loader symptoms you are seeing. The curl and dump will work but boom functions will be hydraulically locked. I am not going to take the time to explain that now just take it as a fact. But EVERYTHING back as its supposed to be and we will start an orderly diagnosis.

Dan

 

[AllenBC]

I am learning! I did not know the fundamental fact that with a closed hydraulic system, like this tractor has, everything is plumbed in series. I think it goes: pump loader valve 3rd func valve backhoe 3-point hitch (should be in lowest position when using other hydraulics) tank. If that's not right, please let me know.

One thing I can't understand is how the dump/curl works with the PB dead ended.

Later this morning I will put stuff back and see if any of the things I have done help the loader arm function.

And thanks for your help!

Allen

 

[old and tired]

...I did not know the fundamental fact that with a closed hydraulic system, like this tractor has, everything is plumbed in series...

Been watching this train wreak... Since you are "learning"... Your L3901 is an "Open Center with Power Beyond" Hydraulic System. Your FEL has 7 hoses connected to it, the 7th one is power beyond. Plain "Open Center" without power beyond, will have 6 hoses.

Back to eating my popcorn...

 

[TheOldHokie]

I am learning! I did not know the fundamental fact that with a closed hydraulic system, like this tractor has, everything is plumbed in series. I think it goes: pump loader valve 3rd func valve backhoe 3-point hitch (should be in lowest position when using other hydraulics) tank. If that's not right, please let me know.

One thing I can't understand is how the dump/curl works with the PB dead ended.

Later this morning I will put stuff back and see if any of the things I have done help the loader arm function.

And thanks for your help!

Allen

I will explain the loader valve operation AFTER we findthe problem. At that point some of it may already be obvious to you.

Dan