Tractor Repair: Ford 1910 Tractor Lift Problems, hydraulic couplers, japanese tractor

Question
I have an '86 Ford !910 4X4 Compact tractor that was my late fathers. I used the tractor in the summer doing some bush hogging with no problems.This winter after a recent snow, tried to use tractor with scrape blade to clear some roads and the lift arms were very, very slow to raise but they did eventually after 20-30minutes warm up time. I checked the hydraulic fluid and it was very milky, hi temp this day was about 29. I shut tractor off, drained fluid and a lot of water with it and replaced with new fluid and filter next day. Hi temp this day about 44. Ran tractor for 30-45min and tried lift and it would try, but not lift scrape blade off ground. I rechecked fluid and it was also milky. Drained fluid again, and refilled next day with new fluid. Hi temp this day about 54. Started tractor, ran for 30-45min and same result. Would try to lift scrape balde but would not lift it off ground. Before final refill, I did take loose some of the return and hi pressure lines and tried to flush them the best Icould with new fluid, then put them back together.I did not recall seeing a suction filter anywhere, but did replace the spin on hydraulic filter up front of the engine next to the pump.Don't know what to check next or how to check output from pump. Any help would be appreciated.

Answer
  Like my profile says, I am not an expert on Asian tractors and I know that this is a Japanese tractor.  It is possible that there is an internal suction screen, but I have no information that I can use to verify that.  I would recommend checking with a New Holland dealer to get a definite answer.  If this tractor has remote hydraulic couplers on the back, a gauge can be plugged in to check hydraulic pressure.  I don't have the specifications for it, but the pressure should probably be about 1800 to 2000 psi.  Low pressure could be a worn pump or bad relief valve.  The only way to accurately diagnose a pump is to measure both pressure and flow with a flowmeter.  A worn pump can still produce enough pressure, but will not have enough flow at that pressure.  If you can get the lift arms to lift a small load, shut off the engine and see how fast the arms settle down.  If they drop more than a few inches in an hour, there is leakage in the lift cylinder or hitch control valve.