I had many years working on those machines, if it is a foot swing the pedals can bottom before the spool fully strokes, Make sure nothing is restricting the pedal movement from going as far as it can without hitting bottom, if it hits bottom remove the shrouding from the console and readjust the clevises so the pedals stand up straighter and make sure the spool fully strokes. if it is hand swing check for full spool stroke there also. If the spool is stroking fully then I would remove the secondary relief valves and the check valves under them and replace the o rings on both. In my opinion what is happening is that the spool is only partially opening the work port, when another system is bottomed the pressure builds back and pressurizes the partially opened spool so it works as it should. I am fairly certain it is a linkage issue, I have dealt with this issue many times, Keep us posted, ahart, The 580 SE is a simple open center system so there is none of the real complicated sensing stuff as the newer models have, the 580 SE was and is real great machine. I was skeptical when the pilot control Cases came out but they have been very trouble free and with a little tweaking are a real beast in the ditch. When I pre delivered my hoes I did a complete flow test on every function and logged it for future reference. Baled me out a couple times when customers complained, got them right there and did another comprehensive flow test and showed them before sale and then ,I actually had one unit test better than the original test