when I was replacing my rotors I had to give a good smack with a hammer. A very very very very small amount of rust had managed to practically unite the hubs and rotors. (I think 1/4 came off without the hammer, which I just used my fist to hit it with). I know it sounds kinda archaic, but hey, they were warped beyond your wildest dreams and I was just careful not to damage anything else it was connected to or near.