to me it sounds like something else, something suspension related. I'd check out tie rods, inner and outer, idler arm, pitman arm, etc. Are you sure that the rotor is all the way back and the tire is mounted correctly? Jack the front wheel up and see if there is any play in it. I'd also make sure there isn't any mud on the inside of the rims or on the control arms. It also sounds like you need a service department not a parts changer.