I had a problem last week with my john deere 8630 losing all hydraulics and gears too,along with steering,i thought the worst,but I started it back up Saturday and everything was working again so I unhooked disc and drove it closer to where I needed it in case it would happen again and it did,i did clean out both hydraulic sump screens,but the problem keeps coming back after 5 minutes of running,the same thing happens,i did find a center screen,and I was told there was one in very back underneath,and now I know theres 2 in them tractors,i couldn't get the main hydraulic screen out till I find a john deere puller to grab onto it with,is there any ideas you all might have,apparently the pump in the rear end under rockshaft is working,but now im thinking the one under the cab may be acting up,they both seem to work but for about 5 minutes then lose hydraulics again,each time,any suggestionsthanks