If you have changed the hydraulic filter and still have the problem then, pull the left rear foot plate loose on the back and you will see a round access cover that will go into rear axle housing. You will see the suction pipe that is bolted to it-take the bolts out of that pipe and get it out of your way. When you pull the round access cover, inside attached to the cover is the internal suction screen-if it is really clogged up you need to rinse and clean the entire housing internally-we have even had to remove the lift cover to clean it properly. Some tractors came from overseas with some type of additive that "slims" in the hydraulic fluid.
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Thank you for your quote about this issue you were having, I was having the same problem and I replaced the rubber flex hose on the line and then pulled out and clean the internal suction screen, and that fixed the problem, it was really clogged up, thanks again and if anyone is having power steering problems or 3 pt lift issues I would suggest cleaning the screen and housing, and replace with new fluid. It seemed to do fine in warmer weather and when tractor was hot, but wouldn't lift at all during the cold weather, I guess in hotter weather the fluid was thinner and able to pass through the clogged screen, but with it clean it works just like it did when new. oh and for the record my tractor is a 2006 model and only has 136 hours, so needless to say this issue can be a problem with any model and with few or many hours on it.