Need help troubleshooting power steering control valve

Springdrl

Member
Need help troubleshooting a power steering control valve on a MF 231. This is the type of valve that moves up and down as the steering wheel
is turned left and right. The tractor has no PS in either direction, and there is strong pressure at the front steering cylinders. I have not tried
adjusting it only because there is no power assist when turning the wheels in either direction.

Thanks.
 
Before carrying out any adjustment check whether you have movement on the spool valve when you turn the steering wheel slightly. Onitial movement of the steering wheel should actuate the spool valve so that the assistance will then start as you turn the wheel further. Check for wear in the links at at both end of the adjustable barrel and also in the bearings at the top of the steering column. If wear is found it MUST be rectified in order to gain full movement,2mm or so to ensure that hydraulic actuation can occur. A small amount of play is not really acceptable.

DavidP, South Wales
 
Hi David. Thanks for the reply.

The spool valve stem does move up and down as the steering wheel is turned left or right from its center position. However, there may be some delay caused by slack, not in the valve valve stem connecting pin, but in the steering wheel itself. The tractor is not on site but in the country, so I will need to check this slack further this weekend when I am there. My thoughts were that once the valve begins to move, power assist should begin.

I feel confident I can fix this problem given knowledge from someone who knows the mechanism well. And very thankfully, it appears you do.
 
I was able to verify this past weekend there is no slack in the linkage of either the sheering wheel or control valve. The valve piston moves as soon as the steering wheel is turned in either direction.

What would be the next step to troubleshoot the system.

Thanks again for the feedback and input.
 
I've rebuilt the whole power steering system on my 240 recently and I think the 231 has the same valve. Replaced the hoses and valve, re-built the pump and re-built the cylinders.

First thing to check is that you haven't been losing fluid. If the level is found to be down and there are no leaks in any of the lines or at the cylinders and hoses or valve, then chances are you need to replace the seals in the pump. There is a seal at the back which goes into the engine, so you wouldnt see a leak as the oil goes into the engine. Seal kits are available and it's not a difficult job.
If the oil level hasn't gone done( and you had sufficient to start with), then the culprit is probably the valve.
I ended up replacing the valve and the turnbuckle above it. If there is even slight movement between the bottom of the turnbuckle and the pin at the top of the valve, you should get a new turnbuckle kit.
My valve was leaking and replacing the seals didnt work. The replacement seems to be well made and fits fine.These valves do fail due to wear and can allow oil to bypass the piston, rendering them useless.
There is a special technique needed to re-fit the valve as there is supposed to be slack in the wheel which must be turned full lock I think to the left, for the first adjustment to get the spool at the required height, to get the pin in the correct position.
Then the piston needs to be turned one full turn.
Once the turnbuckle is connected, final adjustment is best done
in the field. Take a screwdriver with you and as you drive, test the left and right turn. Then with the screwdriver, turn the top of the spool (where the pin goes through), until you have even steering.
If you haven't adjusted the steering/power steering, or made any changes and no leaks are detected anywhere, my guess is that you might need a new valve and I would replace the turnbuckle as well.
Hope that there is something there of help. These valves are a pain to get right. Good luck.
 
It was a full turn of the wheel to the right not left. Checked the book for the instructions and thought they might be of help.
Only other thing I can think of is that the pump has wear but if you have good pressure this seems unlikely.



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(quoted from post at 04:03:56 09/30/16) Thanks Red for sharing this very useful information.

You're welcome.
Forgot to say that if you get a new turnbuckle kit, the top part of it inc the long nut probably wont be the same size, so check all the parts against the old ones first. You only really need the bottom part and the new pin anyway. I think the whole kit is only about $10.
 

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