I have a 1979 2640 and sometimes when I have been running the tractor for a while and shut the tractor off for a little while and restart it I have no hydraulic pressure. At start up I have pressure but only for a few seconds then I loose the steering, three point, and the remotes. After about thirty seconds or so I get pressure back and never have another problem with the hydraulics. When first starting the tractor cold the hydraulics work as they are supposed to. A little history on the tractor When I bought it 6 months ago it had just had the charge pump replaced and new brakes. I have drained the oil, replaced the filter and cleaned the screen. The screen was relatively clean but the was some material in the old fluid. almost a metallic haze. Not sure if this was remaining debris from the previous owners repairs. I am not sure what I need to check at this time.