I'm putting some Ultegra Brakes on my bike and can't seem to prevent the brake body from sliding back and forth when I move them. Either by hand, (pushing them side to side with my finger) or pulling the level the whole body moves which in turn makes the brake arms change position. Am I supposed to really crank down on the nut that passes through the bike from behind until the brake body doesn't move? I'm afraid to do this because the fork and seat stays are carbon. Will I crush it?