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

An essential piece of your driving system is connected to your wheels and bears the entire weight of your vehicle. Without it, your vehicle wouldn’t move at all!

We’re talking about axles.

This part may seem complex (especially as it relates to your vehicle as a whole system), but any vehicle owner needs to understand its function.

Whether you’re a seasoned car enthusiast or a curious beginner, we aim to shed light on this essential part of your vehicle.

Let’s get started with Axles 101!

What is an Axle?

An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle.

In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle.

Sometimes, especially on bicycles, the latter type of axle is referred to as a spindle.

Factors That Decide the Type of Axle in a Car

Several factors determine which type of axle a vehicle needs. For example, the technical requirements and the force generated play a major role in the decision on the type of axis.

Some vehicles have pre-built axles in standard formats. Others have bespoke axles that meet the needs and specifications of the car.

Custom axles are best for cars as they allow more individual control over the wheels. These axles can fine-tune the speed and torque of the wheels.

Types of Axles

There are typically three types of axles – the rear, front and stub axle.

Front axle

For the front axles on vehicles, they can either be a live front axle or a dead front axle. Also, steering is connected to the front axles on cars.

• Live Front Axle: As mentioned before, these axles deliver power to the wheels. These types of axles are commonly used in Front Wheel Drive (FWD) cars, Four Wheel Drive (4WD) cars and All-Wheel Drive (AWD) vehicles.
• Dead Front Axle: These are used to support the weight of the vehicle and also do not actively spin the wheels.

Rear Axle

Similar to the front axle, rear axles can be either live axles or dead axles. For example, a front-wheel drive vehicle will have a dead rear axle. Also, rear-wheel drive and all-wheel drive will have live rear axles, as both types of vehicles send power to the rear wheels to move the car.

There are a few types of rear axles on vehicles. These include Semi Floating Axles, Full Floating Axles, and Three-Quarter Floating Axles. These axles differ based on what support the vehicle needs and where the axle is mounted.

Types of Rear Axles:

• Full Floating Axle: These types of axles do not support the weight of the vehicle; they are used to just send power to the rear wheels through the differential. The weight is instead supported by the spindle that is attached to the axle housing. Also, the wheel hub is attached to this spindle. These types of axles are commonly used on heavy-duty trucks. This is because the axle’s load capacity is larger. Also, because of how the wheels are mounted, an axle shaft can be removed if damaged while the wheel is still able to spin unpowered.
• Semi-Floating Axle: Compared to the full floating axle, the semi-floating axle partially supports the weight of the vehicle while also being used to transmit power to the wheels. The wheel housing connects to the axle through a bolted flange. This type of axle is popular on light or medium-weight 4WD trucks and cars.
• Three-Quarter Floating Axle: The three-quarter floating axle is a combination of the semi-floating axle and the full floating axle. Instead of the axle supporting the weight of the vehicle, the bearings on the wheels are attached to the axle casing and hub. The weight of the vehicle is then moved to the axle casing rather than the axle. Also, this removes any shearing stress from the axle but other loads, such as bending loads, affect the axle. This type of axle is also used on lighter trucks and cars, but is not as popular as the cheaper semi-floating axle.

Stub Axle

The stub axle, also known as a stud axle, is a car axle that attaches to one wheel. These can be used in vehicles such as front or rear-wheel drive vehicles to support the wheels that do not have power going to them.

For example, the rear wheels in a front-wheel drive vehicle may be supported by stub axles. Additionally, these axles have a wheel bearing that supports the wheel hub. These types of car axles also attach to an axle through a kingpin.

If you didn’t know, a kingpin is a large bolt that is used as a pivot. The cotter is a pin or wedge that goes through a hole in the kingpin to connect it to the axle. It makes sure the kingpin does not come out of the connection between the stub axle and the other axle.

There are four main types of stub axles.

Types of Stub Axles

• Elliot: An Elliot stub axle connects to the axle by fitting inside the yoke of the main axle. Then, the stub axle is connected through the yoke by a kingpin and a cotter.
• Reverse Elliot: For the Reverse Elliot stub axle, the stub axle has the yoke and fits around the main axle. The Reverse Elliot stub axle then connects the two axles with a kingpin and a cotter
• Lamoine: This axle uses an L-shaped spindle that connects to the axle with a kingpin and cotter. The cotter also locks the axle in position. This is a common stub axle on tractors and other heavy vehicles.
• Reverse Lamoine: As the Lamoine stub axle forms an L-shaped spindle, the Reverse Lamoine forms an inverted L shape. It connects in a similar manner to the Lamoine stub axle with a kingpin and a cotter.

How many axles does a car have?

The number of axles a car has again depends on your definition of “axle.” Most passenger cars, trucks, and SUVs have two axles—or sets of opposing wheels—one in the front and one in the rear.

Semi-tractors have at least three axles—one in front and two or more in the rear as part of a setup called a tandem axle. In this case, the additional axles help spread the weight of the trailer onto more tires.

Other large vehicles, like dump trucks and cement mixers, have additional axles for the same reason.

What Is The Difference Between A Rear Differential And An Axle?

The rear differential and the axle are both essential components of a vehicle’s drivetrain, but they serve different functions and have distinct characteristics. Knowing their differences will help you understand how power is transmitted from the engine to the wheels.

Rear Differential: The rear differential allows the wheels on the same axle to rotate at different speeds, allowing the vehicle to turn smoothly and efficiently. When a vehicle turns, the outside wheel needs to travel a greater distance than the inside wheel, requiring different speeds.

It’s located between the drive wheels of the vehicle and is usually part of the rear axle assembly in rear-wheel-drive vehicles. It consists of a series of gears, including a pinion, a ring, and a differential gear.

It receives power from the transmission via the driveshaft, which then transmits this power to the axle.

Axle: The axle bears the vehicle’s weight and transmits driving torque to the wheels, providing a place to mount wheels and tires.

There are different types of axles: live axles (which deliver power to the wheels) and dead axles (which don’t transmit power and are mainly used for supporting weight). In a rear-wheel-drive vehicle, the rear axle is typically a live axle.

The axle includes components like axle shafts (which may be solid or split, as in the case of a live axle with a differential), bearings, and, in some cases, the housing that encloses the differential.

In rear-wheel-drive vehicles, the rear axle is connected to the differential, receiving torque from it and transmitting this torque to the wheels. Essentially:

• The rear differential is responsible for adjusting the speed of the wheels on the same axle for efficient turning
• The axle is responsible for carrying the vehicle’s weight and transmitting power to the wheels.

In a rear-wheel-drive system, the differential is part of the rear axle assembly, but it performs a distinct function separate from the axle.

How to Know When Your Axle Is in Disrepair

Because axles are essential to your car’s operation, it’s important to keep them working properly. If you see one of the following signs, you can tell that your axle is in disrepair:

• You hear a loud clunk when you put your car into gear.
• You feel vibrations when you operate your car.
• Your vehicle won’t move forward or backward even though it’s running.

What To Look For When Checking?

Most auto mechanics will check your axle when you get in your car, but you can also do it yourself. You will need to get underneath your vehicle. If your car is low, you may need to lift it off the ground with a car jack or vehicle ramp.

Visual Inspection

The easiest part of the inspection is to take a close look at the boots, which are responsible for keeping the joints lubricated and keeping dirt and water out. The boot has ribs in it that allow it to bend and move with the vehicle.

Check for holes, cracks, or grease leaks. Next, you should check the axle for any scratches, dents, or dings, and for signs that anything is rubbing on it.

Driving Inspection

If you notice that when your axle is in disrepair, it may show signs that

• Your car vibrates when you operate it.
• Your car makes a loud “clicking” sound when you put it in gear.
• Your car is running, but it will not move forward or backward.
• Your car will make a clicking or popping sound when you turn it.

Top 6 Signs of a Damaged or Broken Car Axle

When a car axle breaks, either abruptly (like hitting a curb) or due to frequent overuse (like driving with too much payload), you’ll usually know there’s a problem because the tires simply won’t spin.

However, there are some signs and symptoms of axle damage that might indicate a broken axle—and a visit to an axle repair shop is on the horizon.

#1. Brake Pad Misalignment.

You’ll notice some braking issues once your bent axle starts going bad. The brake pads will begin to shift and become misaligned with the wheels and rotors, and once that happens, you may notice the vehicle skids or slips to a stop.

Over time, the brakes will eventually cease to function at all.

#2. Leaking.

The brake seal on an AWD or 4WD vehicle’s driveshaft may shift and begin to leak small amounts of oil. This will be noticeable when looking at the brake drum.

Axle CV joints can also leak grease, which is not as detectable. However, once this happens, the joints will collect dirt and dry out and deteriorate quickly.

#3. Car Won’t Budge.

The most obvious sign of a broken axle is when your car tires won’t rotate. The car will turn on fine. Its engine will sound happy as a clam when you rev it. There aren’t any electrical issues—no dashboard warning lights, no weird clicking sounds. It. Just. Won’t. Move.

Why does this occur? It’s usually the result of a bent axle joint that’s finally snapped like a Slim Jim. You’ll need a tow truck to haul it to a repair shop near you for an inspection and axle damage repair.

#4. Wheel Wobbling & Vibrations.

Underinflated tires, unaligned wheels and loose lug nuts can also make your vehicle vibrate.

But if you notice any other signs of axle damage, don’t disregard it! Your car is incredibly dangerous to drive once you begin noticing vibrations caused by a damaged axle or other suspension problems.

#5. Vehicle Strains.

Car axles are fairly resilient, but when they’re under pressure, you’ll feel it in the gas pedal. When an axle is bent or damaged, your vehicle might begin to strain. You’ll put it into gear and notice right away that power isn’t getting transferred to the wheels (i.e., it’s slow to get going).

A straining vehicle doesn’t necessarily mean that you have a bad car axle, however.

#6. “Sputtering” Noises.

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

These bad axle sounds will be audible when the car begins to move as well as when turning the wheels.

Car Axle Replacement Costs

On average, replacing an axle will cost between several hundred dollars and $1,200. Front axle replacement cost is about $550 to $740, while back axle replacement cost is typically less, costing $480 to $550 typically.

That said, there are a variety of factors that will influence the cost of repair. Here’s a closer look at axle function, a breakdown of costs, and options for paying for repair or replacement.

Key Points

• Front axle replacement costs between $550 and $740, including parts and labor.
• Rear axle replacement is less expensive, ranging from $480 to $550.
• Labor costs for axle repair or replacement vary from $75 to $130 per hour.
• Getting multiple estimates from different mechanics ensures fair pricing.
• Car insurance typically covers axle damage from accidents, not from regular wear and tear.

Front Axle Replacement Cost Breakdown

The two biggest factors that go into broken axle repair or replacement are parts and labor.

Labor costs vary depending on where you live, but you can generally expect to pay a mechanic somewhere between $75 and $130 per hour. Replacing an axle should take one to three hours, which means you can expect to pay up to about $390 in labor costs at the upper end of the price spectrum. Labor costs for repairs will depend on the complexity of the fix.

The rest of the cost largely comes down to parts. The make and model of your car will determine what types of parts you need. If you have a relatively common vehicle, it will likely be easy to find parts, which can reduce cost. Parts for high-performance or luxury vehicles may cost significantly more.

Another option is aftermarket parts, which are parts not made by the original supplier. These are often cheaper alternatives to brand-new parts.

FAQs.