The axle shafts send the power from the driveshaft that gets the power from the engine by way of the transmission. You may notice a vibration or clicking noise while driving especially while accelerating or turning. It is common for vehicles with excessive mileage to have axle shaft problems. Other parts such as the constant velocity joint or wheel bearing may also be out and need to be replaced. Rear axle shafts often fail due to fatigue or getting damaged from road debris or an accident. A damaged axle should and most times needs to be replaced immediately. Continuing to drive on a damaged axle could cause additional damage to the other driveline components and will make the vehicle impossible to drive.
A car's power of course comes from the engine but how do you get the power to the wheel in order to move the car? That is where that axle shaft comes in by taking the power from the driveshaft and sending it to the wheel. Some vehicles have a live axle but most have half-shafts, one for each side of the car going to the right or left rear wheel from the differential. This design is more common today since most vehicles have independent rear suspensions. The live axle is more common older cars and modern pickup trucks. Axle shafts are usually made out of steel with rubber boots with grease. They are generally long heavy parts and about the same length for each side.
An axle shaft is a vital part for the vehicle's mobility. Improper replacement can result in accidents and/or additional mechanical damage to the car. It is important that a skilled, qualified mechanic replace these parts on your vehicle but it is possible to do on your own. Here are some simple instructions that changing an axle shaft may entail: