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We all know that engine, battery and fuel are the essentials to start a car,  but have you ever wondered how the wheels start moving? 

A component called an axle delivers the driving power from the engine to the wheels that get them going.

However, a car functions on different types of axles that are responsible for several functionalities. Here is a detailed overview of each axle type and the signs to consider for repair or replacement services.

An axle is a steel central rod or shaft that bridges a pair of wheels. It helps the wheels to propel and hold their position to one another. 

A rod extending from the car's transmission and engine is connected to the driveshaft that powers the axle. When the engine rotates the driveshaft, the axles spin and help the wheels go forward and backwards and steer left and right.

Though the number of axles depends on a car's make and model, most vehicles you see on the road have two types of axles. These include light trucks, passenger cars and motorcycles and thus are referred to as "2-axle" vehicles. Therefore, as a rule of thumb, two sets of wheels are equal to two axles. 

By this rule, some vehicles feature three or more axles given the number of tyres and size and can be evenly or unevenly distributed throughout the vehicle as per the requirements.

Various aspects decide the type of axle a car requires. This includes mechanical factors and amount of torque or force produced. Therefore, while choosing a vehicle, do not forget to determine the following aspect to make a purchase as per your driving needs:

• Standard or Custom Made Axles: While you can find some vehicles with a standard pre-designed axle, some come with a customised axle as per the manufacturer's specifications.

  A car with customised axles performs better, given the personalised control over the wheels. You can adjust the wheel speed and torque to a finer degree based on your driving pattern and road conditions. 

• Fixed Axles: In some cases, axles are fixed to the cars, and the wheels rotate as per the axle with the help of bearings. Further, there are vehicles with axles fixed to the wheels as well. 

There are three standard types of axles in automobiles, namely:

Type 1: Front Axle

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It carries the weight of the front section of a vehicle and facilitates steering. Moreover, the front axle processes the shocks from rugged road surfaces. Thus it has a robust and sturdy construction with 1-3% nickel steel and 0.4% carbon steel composition. 

It comprises four parts: a beam, stub axle, track rod and swivel pin. There are two types of front axles, namely:

• Live Front Axle

It transmits power to the wheel. It is in two half axles connected with a differential using the universal joint.  

These two half axles are connected with their corresponding wheels with constant velocity joint (CV) to maintain vertical and pivot motions of the wheel assembly.

• Dead Front Axle

Though not a functional drivetrain component, it rotates freely to mount wheels, bearings and sometimes gears. It has housings that protect it against dirt or water.

Type 2: Rear Axle

Located in the middle of the differential gear and the driving wheels, the rear axle transmits power to the driving wheels from the differential. You will find this in rear-wheel drive vehicles. 

Now based on the design of the axle and method of supporting, there are five types of rear axles:

Rear Axles As Per the Design

It is further sub categorised in two different parts. They are as follows:

• Banjo Axle: Commonly used for smaller and lighter vehicles, a banjo-type axle housing comprises a hollow central member with two hollow tubes. The central housing extends towards each side of the vehicle to protect the differential unit.

• Split Axle: In this design, the wheel on each side is connected to a different shaft to support an independent suspension of both the left and right wheels. Most modern passenger vehicles feature split-axle designs for smoother driving or riding experience.

Rear Axles As Per the Method of Supporting

It is further sub categorised in two different parts. They are as follows:

• Semi-floating Axle: Used in light-duty vehicles, a semi-floating axle comprises an axle shaft on both sides with a spline on the inner end where it meets the differential. It consists of a wheel flange from where the studs mount at the other end. 

  It uses a bolted flange arrangement that connects it to the end of the axle housing. Therefore, besides transmitting power to the wheels, it supports the weight of the vehicle by employing shear force, bending moment, and torsional forces to the axle shaft.

• Three-quarter Floating Axle: A three-quarter floating axle consists of a bearing between the axle casing and the hub to ensure the vehicle load is transferred only to the axle casing. It also confirms that the axle receives the driving torque and side thrust. Besides, it is bolted to the hub to maintain optimum wheel alignment. However, though it has different hubs, each has one wheel bearing.

• Full-floating Axle: It is bolted to a spindle that drives the wheels and thus can be removed without dismounting the wheel. The outer end of the axle shaft floats in the axle tube and thus only transmits torsional drive forces. Hence, a full-floating axle does not bend to bear the weight of a vehicle.

Type 3: Stub Axle

A stub axle is one of the two front axles connected to one wheel in a rear-wheel-drive model. It consists of wheel bearings to support the wheel hub and thus is a sub-assembly of the front axle beam on which a driving wheel mounts.

There are four types of stub axles based on their shapes:

• Elliot: It uses a pin, yoke and cotter connecting the front axle. The swivel pins are attached to the sub-axle, forging to close the axle beam forcibly. 

• Reverse Elliot: It forms a fork-end-like structure to receive the front axle beam and has the opposite arrangement of an Elliot axle.

• Lamoine: Rather than a yoke-like hinge, it features an L-shaped spindle with the thrust washer between the stub axle and front axle beams. It forms an eye to support the beam and stub axles.

• Reverse Lamoine: It forms a beam-end eye to keep up the stub axle. The stub axle and kingpin are combined into an inverted L-shaped assembly with thrust washers at the bottom to secure the front axle.

Though axles are built to be tough, they may break due to poor maintenance, hitting curbs or potholes, or overloading. 

Now, to understand when you should opt for a repair or replacement service, try to notice the following symptoms while driving your vehicle.

• Misaligned wheels: Such conditions lead to compromised cornering precision and vehicle stability. You may find it difficult to drive straight as your car will tilt to either side. Besides, you may notice premature and rapid tyre tears and wear. This is a tell-tale sign of a bent or broken axle and requires immediate attention.

• Unusual Bumping Noises: If you get a clunking noise coming from underneath your car while hitting a pothole or curb, it indicates a damaged axle.

• Compromised Acceleration And Braking Capabilities: You may often experience that, though you can start your car, you find it tough to brake or accelerate. In such circumstances, visit a reliable garage to detect the concern with the axle.

• Grease Leaking From Under the Car: Though this does not indicate a faulty axle, damages can be caused to the axle components, like the CV boot. This also calls for urgent repair. If left for longer, it will build up dirt or increase the grease lubrication leakage, which will be costly to fix.

• Odd Juddering While Driving: Though there can be several reasons behind these, excessive vibration at high speed or any bouncy feel while driving may be caused due to a worn-out CV axle. Address such a condition at the earliest as it may diminish the overall control of the vehicle.

Nonetheless, irrespective of the types of axles- whether front or rear both work differently on front-wheel, rear-wheel and all-wheel drive vehicles. Therefore, always seek expert assistance for accurate and precise solutions.