Hydraulic troubleshooting

[MMagis]

I'm having some intermittent hydraulic problems on my JD 2550, and was hoping someone may be able to steer me in the right direction, at least in regards as to where to look.
Last year while cutting hay in Sept., the hydraulics slowly quit on me. First it was the loader, and things got worse during the 20 minutes it took to get back to the barn. Eventually, even the steering wouldn't work. I didn't have time to get right on it, so it sat in the barn for a while. I started it once or twice in the next month just to let it run, and the hydraulics still didn't work. I started it again in Nov and everything worked fine. This past spring I drained the fluid and checked the sump screen, thinking perhaps a clogged screen was the culprit last year. There was quite abit of "junk", so I was hopeful that was the problem. I used the tractor frequently this summer, with no problems. Last week, after finally having a short dry spell toget some hay down, they quit on me again. I managed to unhook the haybine and get to my garage, at which point nothing worked, steering and all. The next day I started it, and tried working the steering wheel. At first it wouldn't move, but after a few seconds of working the steering wheel it started working and it even built enough pressure to lift the loader, though it was very jerky. But, eventually the pressure faded.
The way it's acting, I'm leaning towards it not being a pump problem, but rather a pick-up problem. Does this make sense? I was originally going to pressure test the main pump, but if the pump isn't getting enough fluid, is it a good test? BTW, the tractor has two pumps, the main pump and an auxiliary steering pump. I had quite a few problems with the steering last spring soon after I bought it. But that was due to the previous owner putting the steering valve back together incorrectly, and I'm pretty sure it's all good now. I assume the steering can't affect the entire system, but I mention it in case I'm wrong.
I hope I didn't bore everyone with too much information. I wasn't sure what was important and what wasn't Thank you for any advice.

 

[LD1]

If you are correct that there is two pumps, one for aux and one for steering, and you are experiencing issues with both when it acts up, whatever the problem is must be common to the two. Do they share a pickup? Share the same hydraulic fluid?

What is the oil level like? IT sounds like its low on oil?

 

[Tx Jim]

1st off there are 2 pumps(trans & frt main hyd) but no dedicated steering pump. Yes faulty steering valve can affect hyd operation. Does tractor have hyd ind pto & hyd hi-lo? How is FEL controlled by ind hyd valve or scv? With engine running,3 pt raised look inside hyd filler hole for spraying oil? It's possible tractor has a bad stroke control valve in frt hyd pump but more diagnostics is required to render correct answer.

 

[MMagis]

I should have added that I did double check fluid level, it's good. I have the tech manual at home, I need to look at it again tonight. I thought the second pump was for the steering, but it's certainly possible I'm not remembering right. I'm fairly certain everything shares the same fluid and pickup, though I'm again going from memory.

Does tractor have hyd ind pto & hyd hi-lo?

Yes.

How is FEL controlled by ind hyd valve or scv?

Ind hyd valve

I'll look tonight for spraying oil.

I apologize if I leave things out or don't know the proper terminology. Though I've been around tractors my entire life, my hydraulic experience is very limited.

 

[MMagis]

Checked for spraying oil last night, nothing. I also spent some time going through the manual, and of course Tx Jim is right, there is no dedicated steering pump. The second pump is for the transmission.
Is it possible for a problem in the main pump to come and go? Both times the hydraulics have quit have been while mowing hay and I’ve been running the tractor continuously for a couple of hours. Could be coincidence, but it made me wonder if something causes it to lose its “prime”.
One other thing that may be worth mentioning. Even when working fine, if I let it idle at low RPMs the hydraulics lose power. I need to increase the RPMs back up and work the loader to get pressure built up. I have a friend whose brother has the same tractor, and his does the same thing so I never thought much of it.

 

[Tx Jim]

Disconnect FEL control valve return line and with both control spools in neutral no oil should exit return hose when engine is running. If tractor has option of hyd hi-lo or hyd ind pto try operating hyd's in both speeds of hi-lo & pto on/off. Stroke control valve(parts key 16) in frt hyd pump can be the problem by not completely seating when required. It's possible hyd oil filter relief valve is stuck partially open or sticking sometimes. Closed center hyd's that are failing require ""extensive diagnostics"" to determine the problem.

 

[MMagis]

I appreciate the advice. I do understand that determining the problem over the internet isn’t likely. I should have worded my original post differently. I guess want I’m hoping to figure out is if I’m able to isolate this as a pump problem, or a non-pump problem. If I knew it was, I’d take it straight to the hydraulic shop down the road and have them rebuild it. My concern is going through all that, and then realizing later that the pump works fine, but something was preventing fluid from getting to it.