Hydraulic question

I'm having trouble with my hydraulics on my JD 2640 tractor. I had it laid up for a while working on the engine. I finally got the engine working great, but now I have a hydraulic issue.

The 3-point goes up and down fine. The front end loader forks go up and down fine....it goes down a tad slow, but goes up great and down acceptable. The problem is with the bucket. It will curl down fine, but coming back up is very, very slow, almost not moving at all. It will curl back up but takes several minutes to do so.

So I don't think it's the pump since the other hydraulics work OK. The bucket going down extends the cylinders, and coming back up retracts the cylinder. The slowness is in the retraction.

These cylinders have hydraulic lines on both ends. One of them has a bit of a leak.

Any ideas or suggestions?

If the cylinders will hold position when the valve is in neutral, good chance the cylinders are good.

I would look closely at the valve. Feel the travel, does it appear to move full distance compared to the other valve? Any wear in the handle or linkage? The spring return feel the same as the other?

If the valve feels good, listen for the engine to load when trying to curl it up. Does it load the engine heavily, the return hoses jump? If so there is a return restriction, probably back to the valve.

If little or no load to the pump, probably the valve not traveling full stroke, something in it, broken return spring, etc.

You have a restriction in the system. We have to find it. Also remember this is a closed center system. You will need a bucket and a stop watch to start with. Send me an e-mail as I have more questions for you. J.

The system won't let me PM you and I don't see your email. I'm glad for any advice...let me know how to contact you. You can email me at sanbog [at} embarqmail dot com.

Here's what I know: It's an old tractor, and my engine quit, so we were rebuilding the engine on weekends. It took us a good number of months to complete. We changed the transmission / hydraulic fluid, so it's good and fresh. Now the engine is running well, but has the hydraulic problem I described above. I changed any hose that looked really old. One of the two cylinders has a small leak....not from the hose, but it seems to be coming from around the main rod on the hydraulic cylinder. The cylinder on the other side has a small bit of rubber seal coming out from around the rod.

Like the other person above, we speculated that it might be the control valve since it sat up for so long. The next step is to just switch the hoses on the two control valves........one works the forks, one works the bucket. However, I might have to get an adapter since for some reason the two valves have slightly different connectors on them. It may take me a few days.

Are you suggesting that I remove the end of one of the hoses, fill a bucket with fluid, submerge the end of the hose into the fluid, then run the system?

Would an air pocket cause my problem? Could bleeding the system possibly help?

(quoted from post at 15:43:28 04/23/17) If the cylinders will hold position when the valve is in neutral, good chance the cylinders are good.

I would look closely at the valve. Feel the travel, does it appear to move full distance compared to the other valve? Any wear in the handle or linkage? The spring return feel the same as the other?

If the valve feels good, listen for the engine to load when trying to curl it up. Does it load the engine heavily, the return hoses jump? If so there is a return restriction, probably back to the valve.

If little or no load to the pump, probably the valve not traveling full stroke, something in it, broken return spring, etc.

Click to expand...

The cylinders will hold position when the valve is in neutral. No problem there at all.

The control valve feels OK, and I didn't notice any obvious restrictions in travel of the handle. The engine does not change speeds hardly at all when the hydraulics are activated. It does not seem to be putting a strain on the engine.

I didn't look for the hoses to jump. I'll keep an eye out for that.....thanks.

I've never pulled apart one of those control valves......I would think they are pretty simple....a piston, O rings, and a spring, I would guess. Right?

Well, I say it didn't put a restriction on the engine.....I didn't notice one. I'll have to check when I get back out there.

Occassionaly the inside liner of a hose will crumple up and act as a one way valve.

After fixing the obvious (leak), go forward from there.

I have come across it before where the gland nut backs off inside the cylinder.
When you curl your bucket down it will push the gland and the rod out fairly easily.
When you try to curl the bucket up the fluid pressure will now be on both sides of the gland and trying to force the rod out which causes one cylinder to fight the other.
50/50 chance as to which cylinder it may be.
Start machine and curl the bucket all the way in
Next loosen the fitting on the cylinder that would normally supply the fluid to extend the cylinder
Next try to curl the bucket in further, if you are getting a lot of fluid coming out that is the cylinder that needs attention.
If you are not then try the same on the other cylinder.