Hey guys, I have a ford 600 with a hiccupping lift. Here is where I'm at. I have replaced all o rings. The lift cylinder oring and backup, lift cylinder to lift cover orings etc. Still corrects or hiccups every 10 to 15 seconds or so. I replaced the check valve seat with a new one and replaced the spring (which was broken)new orings and new ball. Still hiccupped. I forgot to mention I am attaching at least 150 to 200 pound implement for all my tests. Ok the next thing I did was raise lift (loaded) and turn off the tractor with left side inspection plate removed and inspected for leaks with flashlight. I discovered a small weep of oil coming from around the control valve spool. I purchased a used cylinder complete with control valve from a running 600/800 tractor off ebay and installed on mine. Still hiccups. The pump seems to be doing its job and the lift works great ,though it does shutter slightly when I raise the lift. Its just that dadburn hiccupping gosh! About the only thing I haven't touched is the pump relief valve located in the bottom of the sump. Are these available through aftermarket? Anyway I am now turning it over to you guys for your thoughts. I have read some horror stories on hiccupping ford lifts I hope I can trace this down with the help from this forum. This is very depressing. Thanks so much for your time!