The most common rear differential repairs are replacing worn bearings around the carrier and pinion, changing the differential fluid and failure of spider gears or positive traction devices. A fully functioning differential with good parts will function quietly and smoothly, with the exception of mechanical lockers and spools.
Users should change differential fluid, or gear oil, regularly, especially in vehicles with positraction and mechanical lockers that do heavy towing, plowing or aggressive off-road driving. Noise coming from the differential, such as whining or whirring while driving, indicates worn or failed bearings. Spider gears and clutches in the carrier can wear out or be damaged by excessive heat, requiring repair. Under extreme duress or shock, ring and pinion gears can break, causing the differential to fail.