On the left you can see our old synchro ring for the Third to Fourth gearshift, pictured next to the new RSG synchro ring. All synchro rings are a common wear item on manual transmissions. When these wear, they basically lose friction and the result is grinding when shifting. All of our synchros were toast, so they were replaced with new units from RSG. The NV4500 uses two kinds of synchros: multi-piece and single-piece.