Hydraulic bucket leaks down pretty quick.

TimWafer · Apr 3, 2018

The bucket on my old Thomas Skid Steer started to leak down last year and has done nothing but get worse. The boom stays up fine but the bucket uncurls (dumps) constantly unless you keep hitting the pedal every few seconds. No sign of external leakage. To try & diagnose it I temporarily put a couple ball valves in the lines between the spool valve & cylinders. If i close them the bucket stays up fine. To me this means the leak is not internal in the cylinder but must be in the spool valve.
I think this spool valve has check valves in it. Looks like a couple big bolt heads above the spool anyways. Could it be as simple as one of those leaking or do I need to remove the whole valve assembly and tear it down? Was thinking about working on it tonight.

David G · Apr 3, 2018

It is either cylinders or control valve.

Janicholson · Apr 3, 2018

There is a difference between the displacement of the cylinder ram end and mount end. It is the rod taking up space in the cylinder as it moves inward. If both valves are shut,
the difference cannot escape, and the cylinder will lock. If it still stays in place when one of those 2 ball valves is closed and the other open, it is the cylinder. Try it both
ways. Jim

jm. · Apr 3, 2018

Tim a 20 dollar inferred hand held heat detecting device will give you an idea if it is internal leaks in the cylinder. I am with Janicholson in that you ball valves do not prove that it is in the valve. I would bet you have cylinder packing on the piston leaking by.

ohiojim · Apr 3, 2018

I have the same problem on my remotes for Kubota tractor,..leaking in the control valve, thought it was just O rings but the control is just a machine fit on the spools. good luck

farmer boy · Apr 3, 2018

The ball valves prove that it's not the cylinder. Because it's a bucket cylinder and not a boom cylinder, the cylinder is the other way around, and the fluid could bypass without the displacement difference of the rod being an issue. The fluid would bypass from the rod side to the piston side and put the piston side into a partial vacuum, which would only assist in the bypass. The other way around, science says the displacement difference would prevent it from happening.

jm. · Apr 3, 2018

Jim send me an e-mail , I may be able to solve your problem ..jm.

TimWafer · Apr 3, 2018

Trying to wrap my head around what you guys are saying.

So far I put a ball valve in the lines going to the rod ends of both bucket cylinders. Rod ends are down and attach to the bucket. If I close either OR both of the ball valves the bucket remains stationary overnight. If I open BOTH valves the bucket quickly starts dropping. Do you think it can still be an internal leak in the cylinders? I thought that initially , then thought I had eliminated that possibility, and now I'm uncertain.

I do have an infrared gun like your describing. How can that help me diagnose it? I didnt get to do much to it tonight anyways.

Steve@Advance · Apr 3, 2018

With the engine off, can you stop the cylinder by slightly moving the valve?

If so, the spool is not centering, possible a broken return spring.

jm. · Apr 3, 2018

Start the tractor and cycle the loader bucket back and forth several times then take a reading about mid way of each cylinder tube. IF have one bypassing it will be 10 degs. or more hotter than the other. Shows up ever time. After reading what you said above I may be off BUT 90% of the time when we get on in the shop it is cylinder packing, very rare for it to be the valve. As one of the poster suggested may be that the spool is not centering to completely stop the flow but that is easy to check.

carvel minne farmer · Apr 3, 2018

the issue tim is in your spool valves, I had the same problem in my excavater (bucket curl) had to replace the valve.

Frank A · Apr 3, 2018

My opinion is the valve has to be leaking. If you look at the logic of the other replies if the valve is good the cylinder shouldn't move far even if the cylinder is leaking. I think your ball valves proved the cylinder is ok. Its just my opinion for what its worth. Good luck and let us know what you find.

Frank A · Apr 3, 2018

Aren't you saying by your own logic that if the valve is good the cylinder would hold even if it's seal is leaking?

Janicholson · Apr 3, 2018

A leaky piston seal cylinder filled with oil on both sides of the piston (rod facing up or down) with plugs in the ports on both ends, will not compress. It could expand if enough force was put on it to create a vacuum. The piston rod cannot compress the oil in the contained volume. Imagine it with no piston, just a rod. With no place for the oil to go, the rod stays put. Jim

Janicholson · Apr 3, 2018

Your leak is in the valving. The closing of the stated port on the bottom of the cylinder (and leaving the top port open does prove the piston seal is good. Jim

Frank A · Apr 3, 2018

Right, so if the valve is holding then the bucket wouldn't drop even if the cylinder is leaking. They can both be leaking so fixing the cylinder can help but the valve has to be leaking somewhat.

rlp in Co. · Apr 3, 2018

Raise the bucket clear to the top, now open the opposite hose, apply pressure to raise bucket. If cylinder is bypassing oil you will know real quick;

Tx Jim · Apr 4, 2018

(quoted from post at 19:48:05 04/03/18) the issue tim is in your spool valves, I had the same problem in my excavater (bucket curl) had to replace the valve.

Ditto spool valve is leaking internally.

TimWafer · Apr 4, 2018

For the sake of argument at the moment lets assume the problem lies in the valve. Here is a diagram I found of the valve. I'm wondering the exact function of the #10 CHECK PLUGS. Im not clear how this system works and thought the problem might be with one of those but not sure. Any thoughts? Mine actually has three valves ( one additional for accessories) but in this photo the problem would be in the left one without the detent.

Hydraulic bucket leaks down pretty quick.

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