Hydraulic Bleed down puzzle

[powerscol]

On my Bobcat CT 235 I have a puzzle and would like to know the possible fix. First the front bucket curl. Randomly if I try to back drag it will fold (curl) under pressure. If I work it a bit it will be fine for a while.

Now yesterday while working with my 3pt hydraulic top link, it too started creeping, once badly while lifting my goose neck trailer (it would extend under down pressure). I know it is not the cylinder as there are no leaks. Again after working it was fine. It also crept with my drum mower, not holding the pitch I wanted mowing. Every 5 minutes I had to reset. These all connect to the hydraulic block under the tractor (below my right foot). Rear remotes from the side and loader from the front. Control stick from the top.

Is there a single check valve that might control this?

Last I have noticed if I have the 3pt up with a heavy implement like my tiller and I get off the tractor, leaving it at idle to throw a rock to the side, the 3pt will cycle a little bit to keep it up once in a while. So are the 3 point lift arms connected to the same source on my Bobcat.

It is due for a full service, and I would like to have it looked at and be able to explain what to look at when I take it in.

Thanks for the help.

 

[LD1]

For the three things you describe, there are three separate causes/reasons/issues.....though I use the term issues loosely.....as there likely isnt a real issue.....just the nature of how things work. ANd if you can live with the machine as is....there is no need to do anything to attempt to correct.

First the bucket curl. What you describe has been referenced here on TBN before as "floppy bucket syndrome".

Now what causes that is when you move the lever to dump the bucket.....especially pronounced with a heavy load......gravity is trying to extend your hydraulic cylinders to dump the bucket. IF gravity can do this at a rate faster than your pump can pump fluid back into the base end of the cylinder.....you have an air pocket now.

A control valve that has regen as an option (sometimes called fast-dump) can solv the issue. Just use that feature. Sometimes its the second position on the stick. So try pushing your dump joystick further to the right. If you lack regen.....cycling back and forth works the air out and things will be fine....as you have figured out already. You can also just dump ALL the way, and hold the joystick there for a few seconds after the bucket hits the stops. That will also purge the air out.

Second the toplink Two things can cause this. Oil leaking by in the cylinder (no there wont be any external leak). OR oil leaking by the control valve. My money is on the control valve, as ones used for remotes are usually no where near the quality as ones used for FEL's. Your valve is a metal on metal spool. There are no seals or o-rings that seal the different functions/ports off on the valve. All spool valves leak. How much so is a testament to the quality of the valve, and MFG's usually publish acceptable spool leakage rates. You have a few options to correct this if you cannot live with it drifting. 1. They do make toplinks that have check valves. IT isolates the valve from the cylinder and wont allow spool leakage to effect its position. Two drawbacks.....A. You cannot use float with this type of cylinder. B. You cannot move the cylinder without the tractor running. Like sometimes we forget to lower the loader or 3PH. Well, you can still lower them even if the tractor is off. Cannot do that if the cylinder has a pilot operated check valve. 2. Second option would be to install flow control valves. Flow control valves can be completely closed off and isolate the cylinder the same way the DPCV cylinders do. But you have to remember to open them everytime before attempting to move the toplink.

third thing....the 3PHSounds like it is operating the way it should. The 3PH has a feedback circuit. If the 3PH is not where the valve is telling it to be....it senses that and adjusts. Your cylinder inside the tractor could be leaking off a little with a heavy implement, as could the valve, and.....the feedback linkage is sensing it, and bringing it back to where it needs to be. How frequently this happens is a result of how badly worn the valve or cylinder is. To see if the wear is in the valve or the cylinder.....raise the heavy implement to the top and completely close off the drop speed adjust. Just like with the toplink, this isolates the valve from the cylinder. IF it still occurs, the issue is with the cylinder. IF it no longer happens, the valve is the worn out component.

 

[powerscol]

Thanks
Brian has given me a test to do - we will see how it pans out. Could be something as simple as air in the system

 

[LD1]

Possible. But I doubt it based on what you describe. If there was air in the system causing things to bleed off, you would be having issues with the loader lift and power steering as well.

You mentioned nothing about loader lift other than floppy bucket syndrome. And the toplink bleeding off is normal if not using a cylinder with check valves, and a standard spool.

My toplink setup is a 3" cylinder and with my heavy bushhog (1600#), it will bleed off about 1" every 10 minutes or so. Just normal spool leakage under pressure.

What tests did he give you to try?
Does your loader valve have a regen/fast dump position?

A test you can try on the toplink.....put a heavy implement on and raise it up. USe a floor jack, cherry picker, chain hoist, etc to take weight off the tail end of the implement (takes pressure off the toplink) and then disconnect your remote hoses. Then lower the floor jack, cherry picker, or hoist so the toplink it supporting the weight again.

Let it sit and see if it bleeds off. IF it still does it at the same rate.....then yea, could be air in the lines or could be a worn out cylinder. If it dont bleed off doing this, then the issue is not air in the lines, rather spool leakage like I mention.

Same test can be done with the 3PH as I already described in my first post. Raise the implement and shut off the drop speed adjust. If it still does it, then the issue is with the lift cylinder.....which yes could be air. But if the problem goes away, the issue is the valve, and not air.

You mentioned you have been in contact with Brian.....is this one of his toplinks?

 

[powerscol]

I am running several tests today. It did have air in it based on foamy oil at the time of disconnect. More later

Update - its not the cylinder from what I can tell - moved less that 1/16" with my 900lb tiller on it. I think I had air in the system. Ill still have them check out the hydraulics during the service.

Folks - I just wanted to add one thought here. In trying to figure this out, I contacted Brian and his business Fit Rite Hydraulics - fitritehydraulics.com. I had gotten the top link from him. I did not think the cylinder was really the issue, but thought to get his advice. He quickly responded and told me how to do the test and if there was an issue he needed to take care of it. Customer support like this is unheard of these days. If you are considering a hydraulic top or side link, or need to run remotes to the front, please keep him and his company in mind. He knows his work, and stands behind it. I am old and gray and only once before have I found someone like him to stand behind his business.

Brian - Thanks so much for being there. Operator error in this case is the problem as when I re-installed the top link after using my post hole digger (which required the removal). I neglected to fully bleed the air out. Shame on me :ashamed::ashamed::ashamed:.

Brian - You'r tops in my book :thumbsup: May God bless you and yours.

My Bobcat CT 235 is due for the 500 hr service, so I will have the Doc go through everything. Its been a hard season on my girl. I have use her hard over the years, and now it is time for some TLC.

 

[fritz423]

I can't believe never found this site before last week. People are fixing issues I could never get an answer for. This is my new favorite "machine ****" site as my wife puts it!