A damaged differential is easy to diagnose. Because it's such a vital part of the car, you will definitely notice. First, the driveshaft will vibrate, you'll hear the sound of gears grinding, and a whining noise coming from the driven wheels. A quick check underneath the diff should reveal whether you have a leaking problem. If you know your car well enough, you'll notice a change in the handling. Turning into a corner will be harder, and in a worst-case scenario the differential will lock up. Uneven wear on the tires is also a sign of a differential starting to fail. Check out our guide on common car problems for more troubleshooting help.