I used to operate a ferguson 35 and it had a two stage clutch. The first down pressure on it stopped the tractor and a bit more stopped the pto. I have a jd5300 now and it has a lever that engages the clutch with a lever totally separate from the main transmission. I don't care much for the JD system, but it works. I just replaced the pto clutch in mine and found that to engage the clutch they have a throwout bearing that is actually a throwin bearing. I know it is just a problem with my thinking, but I was surprised to see a system set up this way, having to force the fingers of the pressure plate in to engage the pto, thereby having the bearing under load when the pto is being used.