How Does a Differential Gear Work?

Differential Gear Function

An automotive differential gear, commonly referred to as the "rear end," fulfills one major role: it converts the rotating motion of the engine driveshaft into usable rearward or forward motion. The differential gear is located underneath the rear of a vehicle, dead center between the rear wheels.

Differential Gear Teeth

The differential gear is basically just a big cog, or wheel, with ridges and grooves machined into it. These ridges and grooves are what line up with the ridges and grooves of the rear axle, which are in turn connected to the rear wheels. As the engine crankshaft turns, it spins the driveshaft, which is connected to the differential gear. The differential gear redirects the motion of the spinning driveshaft and transfers that motion along the rear axle and ultimately to the rear wheels.

Differential Gear Ratios

Differential gears come in a variety of sizes and gear ratios. The different gear ratios are what determine how easily or how fast the rear wheels spin. Just like the gears on a bicycle affect how easy or difficult it is to pedal, the gears in a differential gear determine the ease to which the rear wheels spin. Low gear ratios tend to be reserved for heavy-duty or industrial vehicles; higher gear ratios tend to be installed in various passenger-type vehicle, as well as high-performance and recreational-type vehicles.

Differential Gear Lubrication

Differential gears require special differential gear oil in order to function properly. As the differential gears mesh with the gears of the driveshaft, friction is created. Differential gear oil reduces this friction and prolongs the life of the differential gear. Differential gear oil is normally changed every 30,000 miles.