Hydraulic woes

[dougmitchell]

Hi all. First time posting here. I recently purchased a MF 431 in good used condition. I believe I got a good deal even with the current issues. I have spent some time searching through the forum finding advice to diagnose my problem but not being very familiar with hydraulic systems I would like to get input from the experts.

When the tractor is cold the hydraulics work well. The FEL drifts - both the lift and the curl. The curl drifts from fully up to fully down in less than 5 minutes. After the tractor has been running for a while the power steering and 3ph are weak. Thinking that the bucket curl issue was related to a bad valve I switched the hosed to see if it that would stop the drift. This was an improvement but the drift didn't go away. Today I was mowing the pasture and removed the bucket so not to worry about the bucket hanging down in the way. I still had issues with a weak power steering system where the steering became unusable at one point.

I want to avoid replacing everything in hopes of correcting the problem. I thought I was zeroing in on a faulty valve but after today I'm not so sure. I need to mention that there is no water in the hydraulic fluid but I do see bubbles after running for a while (I wouldn't consider this foaming). I felt around on the connections looking for one to be hotter than the others but no smoking gun.

What advice do you have to help diagnose the issue. The tractor had filter changes in July 2016 (power steering included) but I don't know if other hydraulic filters were changed. Could this be a single source problem or multiple issues?

 

[dickfoster]

I wonder if it might be sucking air on the hydraulic pump inlet side.

 

[mddorange]

:welcome:
To the TBN forum Doug. We are glad that you joined with us. Sorry to hear about your problem but someone here will be able to help you.
I take it that you are in Joshua, TX?

 

[dougmitchell]

:welcome:
To the TBN forum Doug. We are glad that you joined with us. Sorry to hear about your problem but someone here will be able to help you.
I take it that you are in Joshua, TX?

Yes, in Joshua - a small town south of Fort Worth.

 

[dougmitchell]

I wonder if it might be sucking air on the hydraulic pump inlet side.

How should I go about testing this? I haven't removed the inspection covers yet but will do this tomorrow and see if I can learn anything.

 

[TomSeller]

Foaming can very well be suction problems as mentioned. A suction leak (check all fittings) can introduce air into the system or screens/filters can create too much suction drawing air in. Were they cleaned/replaced?

 

[mddorange]

Yes, in Joshua - a small town south of Fort Worth.

Yes, I know where it is at, that is why I thought of it first. I met my wife in Texas.......... But she was originally from Alabama so don't hold that against me. :laughing:

 

[Rocky J]

I bought a old backhoe that would foam so bad if you filled the hydraulic up then started the tractor it would foam over and out the vent fill cap on the ground until it would make enough room in the tank for all the foam. It ended up being the shaft seal on the pump allowing air into the system. My pump was mounted on the front of the tractor and joined to the front of the crank shaft with a spline shaft.

 

[PILOON]

I vote for air being sucked in via a return line somewhere, at least that would be my first choice.
Look for dry, cracked or rotted return lines. Often many pressure lines do get changed but rarely do return lines as they take less abuse being unpressureised.
Doesn't take much of a crack to suck air and besides there is no leak to indicate where the problem lies.
Upside is return line hose is cheaper than pressure lines.

 

[Xfaxman]

Sounds like it has the wrong type hydraulic fluid in it.