Distorted and warped brake discs should always be replaced and the brake pads should also be replaced at the same time, when replacing the discs great care should be taken to ensure absolute cleanliness and to ensure that no rust or damage is left on or around the hub assembly as this can cause the new disc to be fitted incorrectly and will also cause vibration. - (Always change discs in matched pairs - never one alone and always change pads in sets of four - ie. On both wheels).