Don't *****foot around when removing a cotter; give it a good strong wack. I use a 2 pound hammer with the nut screwed to the end of the threads. The pins are easier to replace than keep from mangling. I typically take one of the old cotter pins to an old bike store, and buy 4 or 5, then I have em in the future. They come in 3 or 4 sizes AND the taper needs to be filed for proper fit.