Couple of things could be wrong. The cheapest is that the loader valve is not a closed center one. If that is the case your dumping the oil faster than the transmission pump can pump it to the main hydraulic pump. So the first thing to do is take the return line from the loader valve off and see if you have flow without using any functions. I usually take the tractor side off and cap the fitting on the tractor. I put the hose in a five gallon bucket with a rag over the top of the bucket. (the rag is to keep from getting sprayed with oil if there is a lot of flow) When you start the tractor there should be little to no flow from the return line. IF you have a lot of flow than the valve is wrong or defective. Your system is a closed center system. Meaning the oil should be stopped at the valve so it can hold pressure and flow until you use a function.
IF the valve is working then you more than likely have a hydraulic pump issue. It can be the charge/transmission pump or the main pump. Either of them can cause your trouble.
If it is not the valve you really need to get a repair manual and some pressure gauges an check what you have going on. Truthfully unless your really mechanically inclined this is some thing you should hire out to some one with knowledge. That also does not mean your local JD dealership. Your old tractor is going to go the youngest cheapest mechanic there. He will not be trained on a JD 4020. The guy right for the repair will need some gray hair to have old enough knowledge to know what to check and repair.
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Today's Featured Article - A Lifetime of Farm Machinery - by Joe Michaels. I am a mechanical engineer by profession, specializing in powerplant work. I worked as a machinist and engine erector, with time spent overseas. I have always had a love for machinery, and an appreciation for farming and farm machinery. I was born and raised in Brooklyn, New York. Not a place one would associate with farms or farm machinery. I credit my parents for instilling a lot of good values, a respect for learning, a knowledge of various skills and a little knowledge of farming in me, amo
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