Car Parts: The Half Shaft

If you drive a front-wheel-drive vehicle, you may have heard the term half shaft before. The half shaft is a necessary connecting piece between each of the front wheels and the transmission box. In general, the half shaft is a very robust part and can stand up to a lot of force and torque. However, like most parts on a car, the half shaft can give out eventually and need replacement. Understanding the function of the half shaft can help you better understand why it’s important to replace this part when it gets worn out.

What is a Half Shaft and What is Its Function?

In front-wheel-drive cars (most cars sold in the United States), a part called a half shaft is required in order to send the power from the transmission to the front wheels, so that the car can move. Front-wheel-drive vehicles feature several benefits over rear-wheel-drive vehicles, like better fuel efficiency, lower manufacturing costs, and roomier interiors. However, successful front-wheel-drive operation will require two half shafts, each of which runs from the wheel to the center of the front axle. Each of the half shafts has a constant velocity, or CV joint on each end to connect to each other and to the wheels.

How can the Half Shaft Fail?

The part of the half shaft that usually causes problems is the rubber boot on the side closest to the wheel. After long periods of use, heat and flexing of the boot can cause a crack in the rubber material. This will cause the grease contained inside to leak out. Once the grease is gone, dirt can build up inside the half shaft, leading to further problems.

How Often Does the Half Shaft Need to be Replaced?

In general, the half shaft needs to be replaced about once every 100,000 miles or so. However, depending on various factors such as the type of car and typical driving circumstances, your car’s half shaft may last for a longer or a shorter time than this. If you notice a clicking sound from the outer wheel when making sharp turns, the half shaft for that wheel needs to be replaced. Grease on the inner rim is another sign that the half shaft has been compromised.

Can You Replace Your Car’s Half Shaft by Yourself?

If you have the proper tools and equipment and are fairly knowledgeable about cars and mechanics, then you can replace the half shaft yourself. You’ll need a jack, socket and breaker bar, a hammer, and of course, a replacement half shaft. First, you’ll need to remove the wheel’s hubcap and axle nut and raise the car on a jack. Remove enough bolts from the suspension to be able to free the half shaft. You’ll probably need to twist the half shaft or pry it loose. Then you can grease up the mounting surfaces and install the replacement half shaft. Align the tires after installing a new shaft. If you’re unsure about any steps in this process, it’s highly recommended that you take your car in to a professional instead. It’s better to pay a few extra dollars for a half shaft replacement than to have the wheels of your car fall off while you are driving.
Half shafts are a crucial part in every front-wheel-drive car. While these are fairly sturdy parts, after long years of use, the CV joints on the ends can give out. If this occurs, the half shaft will need to be replaced. It’s generally a good practice to ask your technician to check the half shafts whenever you take the car in to be serviced. For safety reasons, the half shaft should be replaced at the first sign of breakage.