Every part on a car serves a purpose to keep it moving while on the road. The differential is a key player that works to apply torque (a rotational force) to the drive wheels. Whether the car is front-wheel drive, rear-wheel drive or all-wheel drive, the differential is needed.
How did the differential get its name? The root word of the differential is different. The differential is a system that allows the drive wheels to turn at different speeds, which is required when the car is negotiating a turn. In turn, the outside wheel must travel farther, which means it must travel faster than the inside wheels.
Maybe you’ve heard the term before but are unsure about what this part does and how it works. Keep reading to learn more about the different kinds of differential systems and why they’re important.
What is a Differential?
The differential is made up of many parts. The main components are the ring and pinion gears. The ring gear is attached to the carrier assembly, and inside the carrier is a set of smaller gears.
These smaller gears are often referred to as spider gears, which are made up of another set of pinion gears and side gears. It is this set of gears that supplies the differential action. Following the power flow inside the differential, the pinion gear drives the ring gear, which rotates the carrier.
The carrier then drives the smaller pinion gears, which in turn drive the side gears. The drive axles are splined into the side gears, which then drive the wheels.
The differential is found in the front- or rear-axle assembly on all late-model cars and trucks. In all-wheel drive (AWD) applications, there will also be a center differential driving both front- and rear-axle assemblies.
What Does A Differential Do?
As part of the front and/or rear axle assembly, the differential plays an integral role in how your car makes turns. The differential is designed to drive a pair of wheels while allowing them to rotate at different speeds.
This function provides proportional RPMs between the left and right wheels. If the inside tire rotates 15 RPM less in a turn than going straight, then, the outside tire will rotate 15 RPM more than going straight.
For example, when your vehicle goes around a corner, the wheel on the outside must travel faster than the wheel on the inside. The differential distributes equal amounts of torque to both wheels.
This permits the wheels to react to resistance, or provide traction, to give the wheel more resistance to rotate less. The wheel with less resistance rotates faster.
Some vehicles, such as go-karts, are not equipped with a differential. In this case, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a simple chain-drive apparatus. Front-wheel drive vehicles are designed differently in that the axle and differential assembly is located in the transmission axle assembly or transaxle.
Differential Parts
The following are Differential Parts:
- Pinion Drive Gear: Transfers power from the driveshaft to the ring gear.
- Ring Gear: Transfers power to the Differential case assembly.
- Side/Spider Gears: Help both wheels to turn independently when turning.
- Differential Case Assembly: Holds the ring gear and other components that drive the rear axle.
- Axle Housing: Metal body that encloses and supports parts of the rear axle assembly.
- Rear Axle Bearings: Ball or roller bearings that fit between the axles and the inside of the axle housing.
- Rear Drive Axles: Steel shafts that transfer torque from the differential assembly to the drive wheels.
Types of Differentials
There are four common types of differentials on the market – open, locking, limited-slip and torque-vectoring.
- Open differential – As one of the more common types of differentials which is found in most family sedans and economy cars, the open differential splits the engine torque in two and allows the wheels to rotate at different speeds.
- Locking differential – Also known as a welded differential, this connects the wheels so they go at the same speed. This made turning a little more difficult. Most full-sized trucks have this type of differential.
- Limited-slip differential – Found in sports cars, the limited-slip differential acts like an open differential by default. Once a wheel loses traction, then it shifts to act as a locking differential so there is more traction and control on the road.
- Torque-vectoring differential – With additional gear trains, the torque-vectoring differential can fine-tune the amount of torque delivered to each wheel.
Caring for the Differential
Regular maintenance on any vehicle is a necessity from oil changes, belts, hoses, and other fluids. The differential fluid is no exception. Differential oil is used to lubricate manual transmissions and differentials. It’s similar to the importance of engine oil for the engine. It plays a vital role in protecting the differential and transmission, allowing them to function safely and smoothly.
The spent differential fluid becomes dirty and contaminated after time. Continuing to drive with contaminated fluid is risky as it can put unnecessary wear on components, leading to permanent damage. Signs your differential needs service:
- Whirring noise only when decelerating.
- A howl or whine during acceleration over small or large speeds.
- Rumbling or whirring at speeds over 20 MPH but changes while turning.
- Regular clunking sound every few feet or when starting to move.
- Steady vibration that increases with vehicle speed.
Plan to have your differential fluid is also known as gear oil, or oil in the transaxles changed every 30,000 miles not to exceed 60,000 miles by a trained technician. Clean, fresh oil allows for better protection of the differential leading to a safer ride. As with any component of the vehicle, well-lubricated parts equal optimal performance.