When a rear-wheel or four-wheel drive vehicle travels over uneven ground or road, its driveshaft(s) should move up and down to accommodate road imperfections. To make this happen, automakers use a special type of joints, known as U-joints or universal joints. They connect a driveshaft to a front differential and a transfer case, or to a rear differential and a transmission. On some vehicles, U-joints are also used to connect a differential to a wheel hub via a driveshaft.
Universal joints always come in pairs, which means there is a U-joint on each side of a driveshaft no matter what it is used for. Such design allows for adapting the height difference between the drivetrain components that U-joints connect. This is especially useful on four-wheel drive and all-wheel drive trucks and SUVs as well other bigger vehicles. But regardless of a vehicle, U-joints do the same job, delivering power from one device to another while allowing for up-and-down movements.
U-joints are integral components of your vehicle’s drivetrain. Their failure will lead to an array of drivetrain problems, including the following ones:
Under normal conditions, every driveshaft or axle is perfectly balanced to prevent vibration. If a U-joint wears out, your driveshaft or axle can lose its balance, resulting in excessive vibration.
Clunking noise when switching to drive or reverse
An excessive play in a U-joint can lead to clunking or banging noises when shifting into drive or reverse on vehicles with an automatic transmission. In case with a manual transmission, you may hear such sounds when shifting or during heavy acceleration and braking.
If you notice something that sounds like squeaking brakes when your brakes are not engaged, you might have a U-joint with a lack of lubrication. The sound will change depending on your speed. Sometimes, you may also hear a chirping noise that can be misinterpreted as a sign of a bad drive belt or pulley.
Your vehicle doesn’t move while it is in gear
If your U-joints fail completely, they will not provide any connection from the transmission to the drive wheels. In some cases, you may notice a banging noise if a broken U-joint hits the surrounding parts when the driveshaft spins. This is the worst scenario you may face, so it must be addressed immediately.
U-joint maintenance and replacement
As a general rule, U-joints do not require any kind of routine maintenance unless any specific time/mileage intervals are mentioned in your owner’s manual. Anyway, it is a good idea to inspect your U-joints from time to time to prevent possible damage and unplanned expenses.
Some universal joints are serviceable which means they can be greased to maintain proper lubrication as they age. If so, they should feature special grease fittings to help you with the job. If your vehicle is equipped with such U-joints, make sure to lubricate them using a special grease gun and premium-quality high-temperature grease recommended by the manufacturer.
Whether your U-joints are serviceable or not, regular inspections will help you to avoid a lot of headache and expensive repairs in the long run. You should pay attention to the condition of your drivetrain, and once any signs listed above appear, you should get in touch with your mechanic for a piece of advice. Don’t try to save a couple of dollars by ignoring symptoms of bad joints as this may leave you standing on the roadside.
If you have a bad U-joint it must be replaced as soon as possible. We would not recommend you to replace it yourself unless you’re a mechanic with a strong knowledge of drivetrain operation. Your mechanic should check them for excessive play and replace them in pairs if needed. He or she will also need to rebalance the shaft for its smooth operation.
While U-joints themselves are usually inexpensive parts, the labor involved to replace them can vary depending on a vehicle. Thus, when it comes to some four-wheel drive trucks, the cost can increase as a mechanic will have to disassemble some other parts to access U-joints. Regardless of the labor cost, you should use only OE-quality U-joints recommended by the manufacturer.
If you do want to save some money on the labor cost, you could remove the driveshaft or axle yourself using proper tools, and bring it to your mechanic or repair shop so they can replace the U-joints. However, we do not recommend you to remove any drivetrain parts yourself if you do not have the appropriate experience.