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What is a Differential on a Car and What Does it Do?

Brian England, Mon, Jan 19, 2015

So many times we’ll hear words related to our cars and not even understand what they are. An automotive service adviser may tell a customer, “We need to change the differential oil,” and the customer may have no clue what he’s referring to.  So what is a differential?

Well, here’s a short description of what a differential on a car is.

A differential is part of the front and/or rear axle assembly.  The axle is the central shaft that the wheels on the vehicle rotate around.  The photo below shows where it’s located on a vehicle with a four wheel drive automatic transmission.


The differential allows wheels on the same axle to rotate at different speeds. When your vehicle goes around a corner the wheel on the outside has to travel faster than the wheel on the inside. The differential allows this to happen. Two wheel drive vehicles have one axle and four wheel drive vehicles have two.

On front wheel drive vehicles the axle/differential assembly is located in the transmission axle assembly (transaxle). The differential fluid or oil in transaxles and axles should be changed as part of a preventive maintenance schedule.  It’s part of your transmission service.  Some four wheel drive vehicles require changing the axle oil every 30k miles. On other vehicles it’s every 60k miles or more. This service can lengthen the lifespan of your differential. Consult your vehicles handbook for your manufacturer’s recommendation. If you use your vehicle in extreme conditions then change it more often. In the photo above, the point of the arrow at the front differential is touching the cover.  This protective cover holds the oil in the cavity where the gears are.

The photo below is a 3D rendering of a differential. You can see the gears, and as you can imagine, they need to be kept well lubricated in order to deliver optimal performance.


So, the next time the service adviser mentions changing the differential oil, you’ll know exactly what he’s referring to.

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About Brian England


Brian England, the current president of BA Auto Care (formerly British American Auto Care) got his start with an auto apprenticeship in a small town in the northwest of London. He came to the U.S. in 1972 to work for a Land Rover dealer in Rockville, MD, and a few years later, started British American Auto Care with his wife, Jennifer. A big believer in preventive auto maintenance, Brian's philosophy is to encourage and educate drivers on the benefits of adhering to a regular maintenance plan.