All Hydraulics leak down

[regularjay]

I recently bought a Kubota B7200 2WD/gear trans with a 1630 loader. This thing has oodles of hours and certainly wasn't babied before I got it, but it does run and I'm sure I'll get it 100% eventually. For now I'm trying to figure out a hydraulic problem. This tractor came with a box blade that for now I'm just leaving on as it helps counterweight the loader. But, it won't stay up. It sinks to the ground in a minute or two and that just wont do. Im tired of continually having to raise it up every couple of minutes while I'm working. I would expect that perhaps o-ring for the 3-point lift cylinder might be worn but, the loader leaks down pretty fast too. I'm wondering if these two issues are related. I have no prior experience with Kubotas but I guess that the hydraulics are O.K. otherwise. Most hoses are recently replaced, nothing seems to leak and with a bit of finagling of load/dump the loader will raise the front of the tractor so I suppose the pump is properly strong I just have to get this leak down at both end issue addressed.

To be clear these are internal leaks nothing is on the ground (except my bucket & box blade LOL)

Also, I've got a hose running from a what looks like a fill port under the seat up to the loader valve, I'm guessing its the route fluid not used by the loader uses to get back to the resivoir it just seems kinda "cheesy" as the rest of the hydraulic stuff that doesn't need to flex is hard piped. Is this proper?

Thank you in advance for input or suggestions.

 

[b-rad-g]

If one or both of your cylinders are bleeding by internally it will cause your bucket to drift down. To test your cylinders on your machine you just retract the cylinders all the way, remove the hose or tube at the base of the cylinder, apply full pressure to the retract (rod) side of the cylinder. If oil pours out the open port you have a bad piston seal. This test can also be done on the rod side in the same way.

If all of your functions are drifting you could have some debris in your main relief valve. If this was your problem all functions would be slow and you would have a loss of power in all of your functions.

My guess is you have a couple of bad cylinders.

Good Luck!

 

[J_J]

Can you tell if any of your relief valves are working, you should have two. . A hyd gage will help you trouble shoot the hydraulic system.

 

[JoelD]

If one or both of your cylinders are bleeding by internally it will cause your bucket to drift down. To test your cylinders on your machine you just retract the cylinders all the way, remove the hose or tube at the base of the cylinder, apply full pressure to the retract (rod) side of the cylinder. If oil pours out the open port you have a bad piston seal. This test can also be done on the rod side in the same way.

If all of your functions are drifting you could have some debris in your main relief valve. If this was your problem all functions would be slow and you would have a loss of power in all of your functions.

My guess is you have a couple of bad cylinders.

Good Luck!

This is simple and great advice.

Thanks,
Joel

 

[regularjay]

This issue affects all functions of the bucket as well as the 3 point. The 3 point seems to be signifigantly worse than the bucket but the bucket will sink down and uncurl within only a few minutes.

Bucket lift cylinders were supposedly rebuilt by P.O. This unit seems to have decent strength (I have nothing to compare it to) and speed it just leaks down way too fast.

How would I know if my relief valves are working?

Thanks all,

Jay

 

[J_J]

This issue affects all functions of the bucket as well as the 3 point. The 3 point seems to be signifigantly worse than the bucket but the bucket will sink down and uncurl within only a few minutes.

Bucket lift cylinders were supposedly rebuilt by P.O. This unit seems to have decent strength (I have nothing to compare it to) and speed it just leaks down way too fast.

How would I know if my relief valves are working?

Thanks all,

Jay

Take out both relief valves and clean them. You will need a gage to reset them, and you need to know the operating pressure of the pump. If you are not sure how to do this, let someone who knows, do it for you.

When you extend the cylinder out to the limits, the relief valve should activate. and relieve. Same with the 3 pt. All the operation of hydraulics is dependent on how the system is plumbed. One area might affect another area, etc.

A relief valve is usually a spring loaded ball or plunger holding back the pressure until the spring force is overcome by the pressure of the hyd fluid, and releases some fluid to maintain a certain pressure in order to provide the operating force to the working parts of the hyd system, such as cylinders, hyd motors, etc.

 

[J_J]

On a loader valve, when the levers are in neutral. the cylinders ports are blocked. It would be unusual for 4 hydraulic cylinders to leak down in a few minutes. It would also be unusual for all the cylinder spools in the valve to leak down. If the valve and the relief is good, and if the cylinders are leaking, they will just equalize, the weighted side pushing the fluid to the unweighted side, and if you took off the out hose to the reservoir, no fluid should come out. If fluid comes out, then the loader valve is leaking or relief is leaking. If just one of those cylinders is good, then it should hold the bucket up.
Each set of cylinders has their own spool.

It seems like that there is a problem with hydraulic schematics for tractors, and other hydraulic machinery. Maybe they think that we do not know how to read, etc.

I have a set of manuals for my Case skidsteer, that covers the machine from the front to the back and everything inbetween. Including all electrical and hydraulic schematics.

I have nothing for my Power-Trac.

 

[SPYDERLK]

Even with a leaky piston a double acting cyl that has both sides filled cannot leak down in the compression direction if the ports are truly blocked. Compressing the cyl decreases its volume and the oil has to go somewhere. If it cant the pressure rises to the point that P X rod area will support the load ... or something blows first! Pressure can be very high in such case because of the small area and the relief valve is not in the circuit with the loader valve centered........ So if the arms drop w/o external oil in evidence the lift spool of the valve is definitely leaking.

To check the bucket articulation circuit in the same manner you must observe the cyls while applying compressive load. You can do this by 1st elevating the loader and setting the bucket level. Then place a stand under its lip and float the arms. If the bucket curls under this load the bucket spool is definitely leaking. In neither case have we proved that the respective cyl isnt leaking, but we know whether the valve needs fixing. After proving or getting it to work right the integrity of the pistion seal can be checked using loads that try to pull the rod.
larry

 

[J_J]

I deleted my other post because I was not thinking. Hydraulic lock is just that. If all the ports are secure/tight, nothing will move once set. That is not the end of the story, If the relief valve is in the work port circuit, then, if the load is greater than the cracking pressure, some fluid may leak out, and cylinders will drop a little. Certainly, if the spools are leaking, then the fluid from the cylinders have a place to go, and that is out the out port, and that is a good way to tell if the spools are leaking, is by take off the out hose from the valve, and observing any fluid flow.

 

[regularjay]

O.K. I was doing some work with this machine today and with an empty bucket about waist high I removed the cap from where the return lines goes into the tranny case. (Perhaps a Kubota specific thing, a hose runs from the loader valve to an aluminum fitting behind the gearshift. This fitting has what I assume is a fill cap on it and I'll further ssume that this fitting is screwed into what would be a regular fill port for hyd fluid if I didnt have a loader, seems to be the loader valve "return" path) Anyway with only the weight of the bucket I could see a very slight amount of flow through the hose. I mean very very slight. Could this be an indication of leaking valves in the loader control? Should the loader control seal 100%? I also noticed that the rate of leakdown does NOT seem to coorelate to the load in the bucket. Does that mean anything?

Thanks all!!