Car wheels spin at different speeds, especially when turning. Each wheel travels a different distance through the turns, and that the inside wheels travel a shorter distance thatn the outside wheels. Since speed is equal to the distance traveled divided by the time it takes to go that distance, the wheels that travel a shorter distance travel at a lower speed. Also note that the front wheels travel a different distance than the rear wheels.
If your car did not have a differential, the wheels would have to be locked together, forced to spin at the same speed. This would make turning difficult and hard on your car: For the car to be able to turn, one tire would have to slip. With modern tires and concrete roads, a great deal of force is required to make a tire slip. That force would have to be transmitted through the axle from one wheel to another, putting a heavy strain on the axle components.
What We Do
Like most any other fluid in your vehicle, differential oils degrade over time and begin to loose some of their lubricating properties, Just like motor oil, they need to be changed out from time to time - just not as often!
How Often We Recommend This Service
Differential Service intervals vary considerably from vehicle to vehicle but a 30,000 mile service interval is recommended for most vehicles.