What Is a Differential on a Car?

A well-functioning vehicle is a staple of American society. Whether for work or leisure, a reliable, well-maintained vehicle provides much-needed transportation for our growing travel needs. A well-maintained vehicle requires that you analyze all its components to determine their working order. Most vehicle components each have a specific task or function they serve in order to keep the automobile running. This, of course, helps maintain your vehicle’s retention and trade in value.

Many of us have heard of a vehicle differential. But what exactly is it? How does it work? And what purpose does it serve?

What is a Differential?

A vehicle differential plays a vital role in allowing your car to make turns. As part of the front and/or rear axle assembly, the differential works by driving a pair of wheels while simultaneously allowing them to rotate at different speeds. This function serves to provide proportional RPMs between the left and right wheels. For example, if the inside tire rotates 20 RPM less in a turn than it does going straight, the outside tire will balance this ratio by rotating 20 RPM more than when going straight.

Let’s provide further context; when your vehicle travels around a corner, the wheel on the outside of the turn must travel faster than the wheel on the inside, in order to maintain proper balance and trajectory. The differential acts to distribute equal amounts of torque to both wheels. This provides traction by allowing the wheel to react to resistance by giving the wheel additional resistance, causing the wheel to rotate less. Meanwhile, the wheel with less resistance rotates faster.

Certain vehicles are not equipped with a differential, like golf carts, for example. In these instances, both driving wheels are forced to rotate at the same speed, typically on a common axle that is driven by a chain-drive apparatus. Another variation exists on front-wheel drive vehicles, which are designed differently in that the differential assembly and axle is located in the transmission axle assembly, often referred to as the transaxle.

The 3 Types of Differentials

There are 3 specific types of differentials, all with their own unique functions and purposes.

Open Differential

This type of differential is the oldest and most common design. Open differentials are suitable for numerous makes and models of automobiles, and they are the most simple, reliable, and widely-used type of differential in the market today. Open differentials work when a powered pinion gear, located at the end of the driveshaft, engages with the ring gear. This process transmits power to both the axles through an additional set of gears.

While the open differential is the most reliable and widely-used design, it does have one flaw in its design; when one wheel begins to slip, all power is essentially distributed to the wheel with the least traction, which makes this design inadequate for high-speed racing or rock climbing.


A Limited-Slip differential is similar to an Open differential, but instead of using a powered pinion gear, it utilizes an integrated clutch system. The clutch mechanism in a limited-slip differential locks the left and right sides of the axle together whenever a wheel loses traction. This design is the preferred differential of choice for high-performance vehicles like drag racers, and also an optimal selection for vehicles that are manufactured to tow heavy loads.


The latest and greatest in differential technology, Torque-Vectoring relies on a complex collection of components and sensors that obtain data from the vehicle’s steering system, throttle position, road surface, and other conditions. This gives torque-vectoring differentials the ability to distribute power to each wheel, providing maximum traction during cornering, which significantly increases performance.

What are the Symptoms of a Bad Differential?

A differential is a key component of a properly functioning vehicle, so whatever particular type of differential set-up you have, you want it to work correctly. Differential oil is designed to lubricate manual transmissions and differentials, similar to engine oil. It plays a crucial role in both protecting the differential and transmission, and also enabling them to continue functioning properly.

Over time, the differential fluid becomes dirty and contaminated. When you continue to drive your vehicle with dirty or contaminated fluid, you risk putting unnecessary wear on components, which can lead to permanent damage. Here are a few of the most common symptoms of a failing differential:

  • A whirring noise that occurs when decelerating
  • Rumbling or rapid vibrations at speeds over 20 miles per hour, but subsides while turning the vehicle
  • A howling or whining noise during acceleration over low or high speeds
  • A steady vibration of the entire vehicle that increases with speed
  • A clunking sound that occurs every few feet, or when the vehicle starts to move

Clean, fresh differential oil better protects the components of the differential, which leads to a more functionally operational vehicle...and a safer one, at that. Well-lubricated parts equal optimal performance. With that in mind, it is best practice to have your differential fluid (also known as gear oil, or transaxle oil) changed every 30,000 miles by a trained technician. You should not exceed 60,000 miles before having your differential oil changed and serviced.

Cost of Replacing a Differential

While it may not necessarily break the bank, the cost of replacing a differential is no small fee. Though it’s difficult at times to compare cars when it comes to repair costs, the average rear differential repair costs somewhere between $200 and $400. This entails the cost of the parts combined with the few hours of labor that are required to replace them. However, it can become much more pricey if other elements are needed to complete the repair. For example, if gears are required for the repair, the price of replacing the differential substantially rises. Typically, rear differential repairs that include the installation of a new gear set cost around $1,500, sometimes more when you account for the parts and the labor needed to replace them.

Differential oil is often one of the most forgotten and overlooked fluids in a vehicle, likely due to the fact that it is not serviced nearly as much as other automobile fluids. For this reason, if you suspect that your differential fluid may be dirty, contaminated, or simply overdue for its recommended maintenance schedule, it is advised that you have your vehicle inspected by a professional technician.