Understanding Automotive Brake Parts and Services

Are You Up To Speed With Your U-Joints?

If you drive a vehicle with rear-wheel drive, all-wheel drive, or four-wheel drive, then you have a driveshaft. This critical component doesn't get into the spotlight much, but it's essential for keeping your car moving down the road. While seemingly straightforward, this unsung hero is what helps connect the motive power of your engine to your vehicle's driven wheels.

Although driveshafts aren't typically complicated, they also aren't a single piece of metal. Instead, modern driveshafts usually have a few individual components, including universal joints (u-joints) connecting to the differential or transmission. Understanding your u-joints can help you spot driveline issues and repair them before they lead to severe drivability problems.

Understanding Your U-Joints

Your driveshaft needs to transfer power between your transmission and the driven wheels. For rear-wheel-drive vehicles, a single drive shaft transmits power from the transmission to a rear differential. Four-wheel and all-wheel drive vehicles have slightly more complex setups involving center differentials and transfer cases.

However, it's not enough to just run a rotating shaft between these components. For example, some vehicles may use differentials and transmissions with a vertical offset, which would result in a misaligned driveshaft. Your car also flexes as it bounces down the road, with the rear axle moving with the road surface, creating the potential to bend or break the driveshaft.

Your u-joints make it possible for your engine's power to reach the wheels without causing damage to the driveshaft or forcing it to bind up. As your car travels over rough roads or bumps, the u-joints can take up the slack and allow the driveshaft to move up or down at either end. More importantly, they enable this flex to occur while the shaft is still spinning.

Recognizing U-Joint Failures

U-joints aren't routine service items, but that doesn't mean that they don't require occasional attention. If your vehicle is old enough, the bearings in your u-joints can begin to fail. These failures typically occur for the same reason as any other component containing bearings will fail. In most cases, time and usage will cause seals to break down, ultimately resulting in a loss of lubrication and excess play.

Common u-joint symptoms include loud clunks and noticeable driveline vibrations, often most pronounced at highway speeds. Unfortunately, these symptoms can have overlap with numerous other problems, including transmission issues and unbalanced wheels. However, a rotational squeal or grinding noise may help narrow the problem down to a faulty u-joint.

If you aren't comfortable getting under your car, you should have a driveline repair shop examine your vehicle if you notice any of these symptoms. An experienced technician can often diagnose u-joint problems relatively quickly by checking for excessive amounts of play at the driveshaft ends. Quickly repairing these failures will allow you to avoid more costly problems and performance issues. Call a driveline repair shop for more information.