A differential is a device, usually, but not necessarily, employing gears, capable of transmitting torque and rotation through three shafts, almost always used in one of two ways: in one way, it receives one input and provides two outputs—this is found in most automobiles—and in the other way, it combines two inputs to create an output that is the sum, difference, or average, of the inputs.
In automobiles and other wheeled vehicles, the differential allows each of the driving roadwheels to rotate at different speeds.

Servicing Your Differential

As there is often not an easy, convenient and quick method for changing differential fluid, the service is often neglected. Such neglect can contribute to poor differential performance, premature wear, noise and even premature failure. As changing the used fluid in manual transmissions and transfer cases can be a similarly tedious process, these fluid changes are also often neglected, possibly leading to the same kinds of long term problems, including poor performance, premature wear and possible failure.
Replacing the old differential fluid in accordance with manufacturer recommended intervals can extend the life of the differential components, provide superior protection especially under extreme conditions, and protect against friction, wear and corrosion.