I have a John deere 5400 with a 520 loader. The hydraulic system is working fine in every area except the 3 pt. lift arms. The arms will not raise, they were locked in the up position with the drop rate valve, but when I opened it they dropped and will not raise. I have removed the drop rate valve, checked it out and could not see a problem. I have worked both the lift and draft levers in about every position and combination possible to no effect. Can anyone give me any direction in this matter? Any help would be appreciated. The loader works off of dual remote rear valves and it is working properly. I can notice no load added to the engine when the 3 pt levers are moved.