Thank you. Those 4000 series are good tractors. I just replaced the starter, alternator, voltage regulator, and battery cables on this one. I believe they all were original. It was over charging at 16vdc. Battery cables were getting hot during cranking. Completely different tractor now. Thanks for the comment.
I believe that is a flow control valve or pressure reducing/bypass valve. You can hear it stressing when he hits a certain point. Have you tried to get your adjustment knob moving when there is no hydraulic pressure at the valve or even turning the tractor off and breaking a line to that valve loose just enough to get some movement . I might be way off here but o think you can really fine tune your movements so they are nice and smooth no jerking.
