The differentials in our Rear Wheel Drive, 4 Wheel Drive or All Wheel Drive vehicles are probably the most neglected component on a vehicle. It works in the dirtiest environment on a vehicle and hardy ever complains. It is designed to change the flow of power from one direction to another. It runs in a fluid that has to lubricate all the working parts, do it in extreme temperature variables and do it while operating in the muck and mud. Most modern differentials come lubricated with a synthetic fluid that rarely wears out. However, working gears and bearings do wear out. The metal that wears mixes with the lubricant and after lots of wear can become a metal soup. The more metal in the soup the faster parts can wear. We recommend the fluid to be changed periodically to prevent this wear from becoming a problem. The heavier a vehicle’s load the more often it needs to be changed. It should be changed somewhere between 60,000 and 100,000 miles.