Here at Mackert Automotive, we have customers, like you, from all across the state who write to us with questions or feedback. One common question we're asked is: What is a differential and what does it do? You may have been told your differential needs service, or seen it as an option up on the service menu. Differential service covers a lot of things, so let's first talk about what a differential does.
As you drive through a turn, your outside wheels and inside wheels turn at different speeds. Kind of like the cars going around a race track - the ones driving in the outside lanes have a greater distance to travel than the cars in the inside lanes. The differential is what allows the outside and inside drive wheels to rotate at slightly different speeds so that the tires don't hop or skip while taking corners, or lose traction in dirt or snow. Differentials have gears in them that transfer the power from the drive train to your wheels - which is why they're often referred to as gear boxes. The gears need to be very strong to do this work, and they need to be properly protected so that they'll last.
All vehicles have some form of differential. If you have a front-wheel drive car, your differential is often called a transaxle and is located in the front. If you have rear-wheel drive, the differential is in the back of the car. If you have a four-wheel drive vehicle, you will have a differential in the front and the back - and in the middle as well. The center differential adjusts for differences in speed between the front and rear wheels.
Differential fluid lubricates and cools the gears. Over time, the fluid can get dirty from bits of the gears grinding off. The additives that keep the fluid clean and protect the differential break down over time. So your vehicle manufacturer has scheduled intervals for you to have your differential fluid changed.
Differentials are hard working mechanisms, and, along with the gears in a manual transmission, need to be serviced regularly with high-quality, replacement fluid. Your automotive service advisor can give you more information as to when your next differential service is recommended. You can also ask if they have a record of when the service was last completed.
As with most service intervals, if you are driving under more severe conditions, you will want to service your differential more frequently. "Severe service" conditions are defined in most owners' manuals, and include: frequent starts and stops, short trips, cold weather, hot weather and towing. All these conditions add to the stress of the vehicle and its parts. Also, off-roading in can be especially hard on differentials, especially if you cross streams. Proper service will extend the life of your gears and keep them running more smoothly. If you have never had your differential checked, visit for more information.