What Is Axle?- Definition, Uses | Types of Axles

An axle is a rod or shaft that rotates the wheels and supports the weight of your vehicle. They are one of the most important parts of any vehicle, and come in three main types: front, rear, and stub.

Let us break down the types of axles and see how to choose the right axle ratio for your vehicle.

What is an Axle?

An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be attached to the wheels and rotate with them or be attached to the vehicle and allow the wheels to rotate around it.

In instances where the axle rotates with the wheel, you would usually have bearings or bushings at the mounting points of the axle support.

If the axle is attached to the vehicle frame and the wheel rotates around the axle, then a bearing or bushing is in a hole in the center of the wheel and allows the wheel or gear to rotate around the axle. Sometimes this type of axle is called a spindle, which is the more common term used with bicycles.

What does an axle do?

The car axle is the mechanical link between the rear wheels and the transmission. The axles are part of the system that transfers the power from the engine to propel the car forward while spinning the wheels. Car axles, whether it is a manual or automatic transmission, generally work the same.

When people talk about front-wheel drive vehicles, they refer to the shaft connecting the rear wheels as a “dead axle” because it does not provide power to the rear wheels. Instead, the dead axle provides the ability for the rear wheels to spin while the front wheels are powered.

In rear-wheel drive vehicles, the rotating connection is made at the front wheels instead. “Most axles on front-wheel drive and full-time all-wheel drive cars of today are ‘CV’ or ‘constant velocity’ axles,” says Jaime Boucher, ASE Certified Master Technician and Shop Foreman at Cantin Chevrolet in Laconia, NH.

Another term for the CV axles is half axles because each wheel has its own axle shaft, rather than one axle connecting both wheels.

Factors That Decide the Type of Axle in a Car

The type of axle used with a vehicle can rely on many different factors, both technical specifics and the force generated as part of the vehicle, with each axle playing a purpose or decision in choosing one axle over the other.

Some cars can come with a generic axle, while other vehicles can come with a specifically designed axle that has been designed for the needs/specifications of the car. Custom Axles are better to use with cars because they create more specific control, and they create the ability to tune the speed and torque of the wheels individually.

Types of Axles

There are three standard axle types:

• Rear axle: The rear axle supplies power to the drive wheels. There are two halves that are half-waves connected by the differential. Most rear axles are in tension, meaning they rotate with the vehicle’s wheels.
• Front axle: Front axles are located at the front and assist in steering, and processing bumps on uneven road surfaces. They consist of the beam, the swivel pin, the tie rod, and the stub axle. The front axles must be as strong as possible, which is why they are usually carbon steel or nickel steel.
• Stub axle: Stub axles are connected to the front wheels of the vehicle. Kingpins connect these stub axles to the front axle.

Types of Rear Axles

Not all rear axles are the same; there are three types of rear axles based on the support and mounting mechanism used:

• Semi-floating axle: This rear axle connects the wheel to the flange on the outside of the axle shaft and secures the wheel in place. One bearing supports the axle shaft, and a second bearing is in the axle housing. Since it uses two bearings, the semi-floating axle will also have to be larger than the other types to provide the same torque. Semi-floating axles are typically found in automobiles, SUVs, and medium-sized trucks, Pickups with half a ton and low power.
• Full-floating axle: The name implies that this type of axle will “float” in place due to its use of two bearings. This type of axle also maintains the position of the axle shaft by only transmitting the drive torque. Fully floating axles are designed for larger vehicles such as medium to heavy-duty trucks. Some medium-sized trucks that have a larger towing capacity or that have all-wheel drive will also benefit from fully floating axles.
• Three-quarter floating axle: This type of axle is slightly more complex than semi-floating axles; it is more reliable and will assist in maintaining wheel alignment and handling side thrust and driving torque.

Types of Front Axles

Vehicles have two main front axle types:

• Dead Front Axle: These are fixed axles that do not rotate with the front wheels. Most dead front axles and differentials employ a type of housing that prevents water and dirt from entering.
• Live Front Axle: Live front axles transmit driving power from the gearbox to the front wheels, whereas dead front axles don’t transmit power to the front wheels.

Types of Stub Axle

As The Engineers Post explains, there are four types of stub axle:

1. Elliot: This type uses a kingpin, a yoke, and a cotter to connect to the front axle.
2. Reverse Elliot: This type has the opposite arrangement of a standard Elliot stub axle.
3. Lamoine: This stub axle type has an L-shaped spindle instead of a yoke-type hinge.
4. Reverse Lamoine: It has the opposite layout of a standard Lamoine stub axle.

How Many Axles Does a Car Have?

The number of axles on a car depends on the type of vehicle. In most cases, cars have two axles to turn the wheels. Other larger vehicles that carry more passengers or have more wheels have more axles.

It is easy to see how many axles your car or other vehicle has. Just look at your car from the side and count the sets of tires. Most cars have 4 tires or 2 sets of tires (1 in the front and 1 in the rear). Two sets of tires are indicative of 2 axles.

• 2 axle vehicle – 2 axles. Examples are bicycles, motorcycles, ordinary cars, light trucks, medium-duty trucks (like the Chevy Silverado 3500, Ford F-350, and Dodge Ram 3500 as “duallies”), and some class 8 trucks (package delivery company trucks that run double trailers, and triples where legal, often run these two axle tractors).
• 3 axle vehicle – 3 axles. These would include straight trucks with a pair of rear axles to handle the extra weight coming from the cargo, a Greyhound bus, and some full-size RVs. The majority of tractor units for a semi-trailer also have three axles. Also covered are 3 axle combination vehicles with small utility trailers (For exampl,e the Ford Focus and Honda CRV). A vehicle like a stretch limousine has three sets of tires, thus it must have three axles.
• 4 axle vehicle – 4 axles. Examples include Tri-drive highway tractors that are used for hauling oversize loads, dump trucks with lift axles, and concrete mixing trucks, which have two steer axles and 2 drive axles. A 4 axle combination vehicle would just be standard highway tractors with single axle trailers, or trucks with 2 axles that are shunting standard 2 axle dry vans around a trucking company’s yard or distribution center. Alternatively, it could be a pickup with a 2-axle travel trailer.
• A large freight truck will have 5 axles in total. 3 are located on the truck, and the other 2 are on the trailer. An 8-wheeler also has 5 axles; one in the front, 2 in the middle positioned where the trailer is attached, and then 2 at the back of the trailer. The axles found underneath the trailer have 4 wheels (instead of the normal 2) per axle. There are vehicles with even more axles, but these are specialized vehicles designed to haul the gigantic and long loads.

How to Know When Your Axle Is in Disrepair

Keeping your axles functioning properly is essential to your car’s operation. You may determine that an axle is not functioning properly if you:

• Hear a loud clunk when you put your car in gear.
• Feel vibrations when you drive your vehicle.
• Your vehicle will not go forward or backward even though your vehicle is running.

Why Should You Inspect Your Axles?

Conducting regular axle inspections is a crucial part of car care. Spotting a problem early could possibly save you thousands in repairs because axle repairs, for many vehicles, can vary drastically in repair if you need to replace axles.

What To Check for During When Inspection

When you take your car to a mechanic, the mechanic will inspect your axles regardless of any problems you indicate – but you can also inspect them yourself.

You will not need any tools, but you will need to be able to see under your car. If your car is low to the ground, it may be worth it to buy yourself some vehicle jacks or vehicle ramps.

The Visual Inspection

One of the easiest parts of the inspection is visually inspecting the boot that keeps the joints lubricated and keeps water and dirt out, which has ribs that allow it to flex and move with the vehicle.

Inspect the boot for any holes, splits, or leaking grease. After the boot, you should inspect the shaft for any knicks, dings, dents, and rubbing.

You will also want to look at the clamps that connect the boot to the shaft. Look for any leaks there, too.

The Drive Inspection

One of the best ways to tell if there is anything wrong with your axles is by the sounds it make while you are driving. If you ever experience any of these issues, please seek help, as this can be a sign of axle disrepair.

• When you put your vehicle in gear, does it make a “clunk” sound?
• Is there vibration when you are operating your vehicle?
• Do you hear a popping or clicking noise when reversing or turning?
• Your vehicle is running, but it will not move forward or backward.

Top 6 Signs of a Damaged or Broken Car Axle

When a car axle breaks, whether it’s sudden (like hitting a curb) or from too much frequent usage (like permanent overload), you usually know there is a problem because the tires just won’t move.

That said, there are some hints and signals of axle damage that may suggest a broken axle, and a short trip to the axle repair shop is on its way.

#1. Car Won’t Move.

The most obvious symptom of a broken axle is when your car tires will not rotate. The car turns on fine. The engine sounds happy as a clam when you rev it. There are no electrical issues – no warning lights light up on the dashboard, no random clicking sound. It. Just. Won’t. Move.

Why is this? Typically, it is because of a bent axle joint that has finally erupted like a Slim Jim. You’ll need a tow truck to take you to a repair location for inspection and axle damage repair.

#2. Vehicle Strains.

Car axles are fairly resilient, but when they’re starting to strain, it will be evident in the gas pedal. When an axle is bent or broken, your vehicle might start to strain. You will put the car in gear and immediately realize that the power is not transferred to the wheels (in other words, it took forever to move).

However, a straining vehicle does not mean that you have a bad car axle. The car straining should be accompanied by a bad axle, which is listed below.

#3. “Sputtering” Noises.

Along with straining to move, the vehicle also may make sputtering, bumping or clunking noises. This occurs because the axle is not able to transfer adequate power to the wheels.

You will hear these bad axle sounds not only when you begin to move the car, but also while turning the steering wheel.

#4. Wheel Wobbling & Vibrations.

Wobbling or vibrations can also be caused by under-inflated tires, wheels that aren’t aligned correctly, or lug nuts that are not tightened securely; however, if you are starting to notice other signs of axle damage, please don’t ignore them! Your automobile is extremely dangerous to operate at that point, whether the vibration is from the axles or anything wrong with the suspension. 

#5. Misaligned Brake Pads.

You will likely notice some type of braking issue once your bent axles start going bad. The brake pads will start to shift and come out of alignment with the wheels and rotors, and then you may notice your vehicle skids or slips to a stop. Eventually, the brakes will stop working altogether.

#6. Leaks.

A brake seal on the driveshaft of an AWD or 4WD vehicle may sometimes shift in place and leak small amounts of oil, which you will likely see when inspecting the brake drum. 

Axle CV joints can also leak grease, though this is harder to see. Once this happens, grease collects dirt and dries out quickly, leading to failure of the CV joints.

How to Select an Axle Ratio for Your Pickup Truck?

Besides its unique torque, engine, and transmission specs, many trucks also have custom axle ratios. A ratio of 3.55:1 means that the driveshaft will make 3.55 revolutions each time that the wheels make one revolution.

A standard final drive ratio tends to work for most drivers, – if you are not planning to load it significantly. If you are towing heavy trailers or planning on pulling anything significant, you may want to get the highest final drive ratio you can.

Are car axles covered by Insurance?

If your car axle was damaged or broken as the result of an accident or hazard, it could be covered by your car insurance (depending on your specific policy). You would not be covered for wear and tear or aged components.

You can purchase warranty coverage for major components like the engine and transmission, but this is separate from insurance and has its own rules and restrictions.

FAQs.