Before they are used the first time and then again every time before use if they have set for a while without use, the clutch springs need to be backed off so that the clutch can be slipped and then readjusted. The fiber discs are bad about rusting and / or sticking to the steel plates. If they stick and you hit something solid, the gear box, PTO shaft, U-joints or gears in the transmission can be damaged. If the PTO shaft can't move like when the PTO is in gear and the tractor is off, you shouldn't be able to turn the blades by hand. Think about it this way. If the clutch slips that easy, how could enough power be transfered to spin the heavy stump jumper and blades up to speed? Also if they turn that easy, there will be no tractor power transfered to the blades to cut brush and thick grass would slow the blades to a stop. If the tractor is putting out power and the clutch is slipping, then the clutch plates will burn out.