[AT] MF 255 power steering

[Cecil Bearden]

If I remember right, that pump is driven from the timing gears of the 
engine.  I think it is on the left side.  There were both Gear and vane 
pumps used.  if it is a vane pump, you can make the vanes from some 
sheet bakelite.   I found some one time on Ebay, or you can search for 
pump parts.    If it is a gear pump, you can put the end plat on a 
surface grinder and reface the grooves out of it.  The gears are usable 
if not scored too bad on the sides.   I did this on a $1800 J Deere pump 
on a 400 Backhoe.   Some of the pumps had replaceable wear plates, if 
they are the same on both sides, you can turn the wear plates over.

Cecil in OKla


On 10/11/2016 8:21 PM, Dennis Johnson wrote:
> Len,
>
> My guess is a worn pump. All pumps start loosing efficiency soon after they are installed. One significant difference in pump types is the rate that the efficiency changes. Gear pumps tend to have the greatest wear rate and efficiency lose with time. Vane and Piston pumps tend to loose efficiency about half as fast as a gear pump for a long time. One significant difference is that the vane and axial piston pumps get to some point and then the wear or efficiency curve slope changes drastically and they go almost zero efficiency within a fraction of a second. I have seen a failure like this when a hydraulic pump manufacturers engineer was witnessing a test we were doing and we caught the failure on a high speed recorder  and it all happened within a second.
>
> With gear pumps the efficiency can go down to 10 or 20% volumetric efficiency and still pump a little bit, especially when the oil is cold (thicker).  You might be getting 20% or 30% volumetric efficiency with cold oil, and then then drop down to 5%, 10% or even 20% volumetric efficiency with warm (thinner) oil. This may not be enough to do much more than handle internal valve leakage, so there is not enough fluid being pumped to do the steering, or the volume is so low it makes the steering operate very slow.
>
> Good luck
> Dennis
>
> Sent from my iPad
>
>> On Oct 11, 2016, at 7:17 PM, Spencer Yost <yostsw at atis.net> wrote:
>>
>> I once had this problem in the 1970s with a truck where the cheap,  riveted pulley/sheave separated and was replaced.  The replacement was wrong and did not turn the pump fast enough at low RPM's.  It was pretty obvious and so your situation sounds different but just a thought.
>>
>> ATF works better warm.   Might give that a try instead of PS fluid.  Make sure all air is out of the system.   A fluid swap is a good time to do this.
>>
>> I am not crazy about the pump idea. My experience is they fail at all temps or at least exhibit some subset of symptoms even when cold. But I'm not  terribly experienced either, so take that with a grain of salt.
>>
>> I hope someone with more experience jumps in....
>>
>> Good luck!
>>
>> Spencer Yost
>>
>>
>>
>> Spencer Yost
>>> On Oct 11, 2016, at 4:11 PM, Len Rugen <rugenl at yahoo.com> wrote:
>>>
>>> My MF 255 is one of the later models with the AD236 Diesel, but I don't know if that matters on the power steering parts.
>>>
>>> It has always been hard to steer at slow RPM after it gets warm, it was usable, but now it's getting worse.  I've had it several years, when I got it, the inlet screen in the power steering pump was damaged, so not straining anything, I replaced it the screen at that time and put in mostly new fluid, I'm sure some was left in the system I didn't get out.
>>> I've found a new pump for less that I could get the tractor hauled to the dealer.  What are the odds that a new pump will fix it?  Anyone care to venture a guess?
>>>
>>> Len Rugen
>>>
>>> rugenl at yahoo.com
>>>
>>>
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