Replacement Axle & Differentials Parts

What are Axles & Differentials?

At the heart of your vehicle's drivetrain is still a simple mechanism: the wheel and axle. The two wheels mounted on either end of a long shaft are still one of the most important mechanisms of transportation. But most modern drivers don't put a lot of thought into the car axle and differential until there is a problem. Fortunately, NAPA carries a plethora of replacement axles, differentials and related parts should you find yourself needing a repair.

The axle and differential are two essential components of a vehicle's drivetrain, which is the system that transfers energy from the engine to the wheels to move the vehicle. The axle is the rod that connects your wheels to the chassis, and the engine spins the axle shaft to power the drive wheels. Vehicles with four wheels have two axles with one on the front and one on the back. The differential divides engine power in two and allocates it to each wheel accordingly to make turning easier and more accurate.

How Does a Wheel & Axle Work?

Whether your vehicle uses front-wheel drive (FWD), rear-wheel drive (RWD), four-wheel drive (4WD) or all-wheel drive (AWD), the two main jobs of your vehicle's axles are the same. Axles need to transfer energy from the engine to the wheels and make them turn while supporting the vehicle's weight, including the passengers and cargo. Depending on the drivetrain, some axles will do both while others will only support the weight.

Most modern vehicles feature two kinds of axles: the front axle and rear axle. They are either powered or freewheeling depending on the driveline configuration. A RWD car has freewheeling front wheels while a FWD car has freewheeling rear wheels. Regardless, the different types of axles are a crucial part of your vehicle's drivetrain. Axles also work with your suspension system to absorb shocks from driving over uneven pavement and rough terrain. That's why they are usually crafted using steel to ensure they're as sturdy as possible on heavy-duty trucks and vintage cars.

What Does a Differential Do?

Imagine for a moment that you're taking a right turn in a vehicle with rear-wheel drive or all-wheel drive, perhaps in a slick BMW 525i or a Subaru WRX. To prevent the right rear wheel from slipping and ensure a safe, reliable turn, the left rear wheel must turn faster than the right. That means both wheels must turn at different revolutions per minute (RPMs). That's where your vehicle's differential enters the game.

Differentials or "diffs" are found on nearly all modern vehicles. There are a handful of varying types of differentials, but they all divide power/torque from the engine and allocate it accordingly, allowing the wheels to rotate independently and at different speeds. Front-wheel drive vehicles have a differential located on the front axle near the engine and next to the transmission. These are also called "transaxles." Differentials on rear-wheel drive vehicles are located on the rear axle; the oddly shaped box on the rear axles of lifted trucks. All-wheel drive vehicles have a center differential to control and allocate power to all four wheels.

Signs of a Bad Axle or Differential

Let's hope you never drive over a railroad crossing, pothole or speedbump and immediately notice any of the following:

• Vibrating or shuddering under the car
• Rumbling, sputtering or bumping noise
• Wheel wobble
• Sluggish steering response

If so, it's time to get your tools and jack stands, hop on your creeper seat and roll under your car to check for damage. Rough terrain with sudden drops or loose rocks can damage your axles and make steering difficult or unsafe. If you hear new, odd noises from under your vehicle, like whirring, whining, howling or grinding, it is possibly also time to check your differential.