Ummmmm.......I know that my CK20 had an internal over-run clutch but didn't know my CK30 has one being it has a 2 stage clutch. Here's how I kinda found out 'bout this internal slip clutch on my 30 gear drive, a couple of months ago when mowing a field with my rotory mower I happened to run over some old layed down fencing not visible in the high weeds. Well the mower grabbed it, wound it up tight in the blades and locked the mower up, the fence wire was so tough that the tractor broke traction! The wheels was a spinin' but the PTO shaft wasn't turnin'. I pushed the clutch pedal all the way in, disingaged the PTO and after a few minutes of tractor power, was able to free it from the snag. I had to remove the blades from the mower to remove the wire mess! I went and finished the mowing, everything worked fine.
Concerned that maybe something might have gotten damaged, I called my dealer and told him what had happed, he chuckled a little and said not to worry and it was normal for it to slip and they were made that way, so that's where I got my experiance and info from. And yes, I have a new PTO clutch coming