MF 251 XE Hydraulics Issue

[Dave E]

Hello all. Bear with me this will take a minit.
I have a 2000 model 251XE I have owned since it was 2 years old with a Bushog loader on it I installed years ago. Past few years intermittently lift arms would fail to rise or would drop. Would only raise at idle. When reved up they would fall. Eventually split tractor and went through pump out of desperation and found no fault, reassembled and had same issue. Now the loader sounds and acts like it has air in system, growls and is jerky, it has an auxiliary pump inside.

What we have determined, by running the tractor with the lift arms and top removed, for some reason the main pump is aerating the fluid, and the aux pump suction is picking it up causing the aeration issue.
This tractor has a small tube that runs from the tri angular cast cover underneath which secures the strainer, to a pressure/vacuum switch under the seat with a wire connected to it that is supposed, somehow to turn on a light on the dash if the strainer starts to plug up.

Now the interesting part. When the switch is removed from the small tube and allowed to be open, it pulls a vacuum on it, and this is causing the fluid to aerate and the loader growls, BUT, with it open, the rear lift arms operate as they should. If you plug the line off so no vacuum flows, aeration does not occur, the loader operates as normal, no growling or jerking, but the lift arms will not raise, only at idle with they attempt to rise.
I can find no one that can tell me how this little tube/switch outfit is supposed to work, or be affecting this system, or how to fix this thing. It has in its previous years I have owned it worked perfectly fine and no one has done any hokey foolin with it.

Sorry for long post and thanks for reading and any help or insight anyone may have or who might know. Thanks Dave.

 

[Fedup]

As I see it, the "light" involved is a waste of time. If the system works with the tube plugged off, then plug it permanently and get back to work. Massey has been building those tractors for over seventy years using the same lift system without any "idiot" lights and gotten by just fine. When the screen gets plugged the hydraulics will tell you without any lights.

 

[Dave E]

I get it. I agree. But it doesn’t work properly with it plugged off or open. As I stated, when it’s plugged the auxiliary system works perfectly, and the 3 point doesn’t. When it’s unplugged, the 3 point works right but the auxiliary system is aerated causing it to growl and be jerky.

Can find no diagram of this system. My manual doesn’t even show an illustration with it being there. Thank you for your response!

 

[Fedup]

I'm not sure what "diagram" you're hoping to find. As I see it, that model was made in Brazil. Some tractors built down there are mostly similar to UK built units, but not entirely. The parts book shows two lift pumps. One made in UK and the other ??? Could be made locally.

That said, I ran into something similar a couple of years back on a 270. (that too, is a bit of an Bastard child compared to other models) I couldn't get the lift to work. Spent days working on it, rebuilding the pump (twice) had it apart numerous times. It has a very similar lift pump suction manifold to what the book shows for the 251xe, in that there is a valve of some sort in there that I could never find or figure out the purpose of/for. I tried it with the valve tied open, tied closed, out entirely, and couldn't make the pump work. For some reason the pump wouldn't pull oil through the suction screen without the vacuum created moving the control valve spool to the lower position. As such, the lift would start to work if I cranked the engine with the starter, but as soon as the engine started the lift would drop again and never come back up. I finally determined this was happening and tried it without the screen. It worked fine like that. Whether the valve I mentioned had anything at all to do with the problem, I never figured out. What I ended up doing was modifying the screen so it could draw fluid into the pump with less restriction (and yes, slightly less filtration) and it has been working ever since. I would suggest you try that. Just drain the oil, remove the screen entirely, put the oil back in and try it. It may be no help at all, but you won't know unless you try it.