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You have a sticking control valve. This can be a combination of problems. The first thing that can cause it to stick is dirty oil. The N hydraulics has no filter system and any and all foriegn material that enters the differential, transmission or the lift settles in the lower reaches of the lift. Unfortunately that is the home of the control valve and oil intake too. The best thing to do to remedy this dirty problem is to pull the pump out of the tractor and clean it. The other thing you can do is to drain all three places and rince the lift out with 5 gallons of kerosene. Pour it in as fast as you can through the inspection hole. Allow it to settle for a while and then pour it through again leaving the residue in the bottom of the container and discarding it. Do this untill no residue is in the bottom of the catch container. Add new oil. If you do take the pump out you should take the control valve and spring out of the pump and inspect the control valve for any wear patterns that might make it want to stick. The control valve can be polished by turning it in some wet or dry 300 grit sandpaper to smooth out any imperfections. This will make the vavle fit a little looser in it's bushing but if you don't get too carried away at it the difference in size will be inconsequential. The return spring that pushes the control valve back to the unload position can break or become weak from age and fatigue. Make sure it has enough tension to do a good job of pushing the valve back. If it is too weak the valve will not come back to the unload position with a heavy load on the lift no matter how clean or good fitting the valve is.
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