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JD850 Hydraulics issue

Stan On my JD850 that I bought last summer, the hydraulics are very slow, and sometimes will not work at all on colder days (below 55F). It takes warming it up for 20 min or longer before I see any improvement. When it does start to move, it's a little jerky. I changed the fluid, filter, and cleaned the wire screen. This seemed to help some, but still not up to par. I have also noticed a light rattling sound at the front of the engine at higher rpm's, but not sure this is from the pump. The pump is not serviceable according to the manual. Got any thoughts on whether it's the pump, or maybe another problem?
Stan This is the type hydraulic fluid that I used;

derek Try increasing the spring in the pressure relief valve. We have had similar trouble and foudn the spring in the valve had lost a bit of tension. We put in a thin washer on top of the spring which fixed everthing.
Stan Speaking of relief valve....I have noticed that the adjustment knob has very little resistance when turned. It still will screw all the way in to hold the lift position, but when screwed out to adjust lift rate, the knob turns very freely after the 1st full turn out. I remember my previous Yanmar tractor having resistance all the way out, and the hydraulics worked great on it. Sound normal to you?

Stan I still have not figured this out. I tried checking the pressure with a gauge, but there was no reading. I'm not totally sure the port I used is the correct one. I have the power steering diverter block next to the lift lever. It is different from the one pictured in the manual. The only test port I could find on the block is marked T beside it. It is directly above the power steering line that is also marked T. Can anyone tell me if that is the correct port for pressure readings?

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