When a u-joint fails, it can cause a vehicle to lose control and leave the driver stranded. There are potentially many other undesirable consequences. This is why understanding what causes u-joint failure is important for safe driving.

Let’s discuss the most common causes of u-joint failure:

1. Lack Of Grease

This applies to both greaseable and maintenance free u-joints alike.

Greaseable U-Joints

Greasing the grease-able style of u-joints regularly is the best way to prevent failure. It ensures that they stay lubricated and functional. Yet, it’s possible for a u-joint to fail even if it’s well greased. U-joints are exposed to the elements, which means moisture can make its way inside them. When that happens, the u-joint can seize and fail.

Maintenance Free U-Joints

Some maintenance free u-joints have a teflon coating inside in addition to grease. This helps to prevent corrosion. This should be enough to keep your joints well lubricated for their entire service life. But sometimes they still fail. If they do, it may be because of improper installation. Inspect u-joints during installation to make sure that the u-joint caps installed correctly. They also may fail due to excessive vibration.

Lack Of Grease Due To Vibration

U-joints don’t like vibration. A driveshaft that is out of balance can cause enough vibration that the life of the u-joints will be shortened. The vibration forces out the grease and causes the metal components to grind against each other. Eventually this leads to failure.

Lack Of Grease Due To Excessive Heat

U-joints don’t perform well under extremely high temperatures. The grease inside them supplies lubrication to the metal components. If too much heat builds up, it can cook the grease so that it fails to protect the metal. This can happen if a u-joint is located close to a source of heat, such as a muffler.

2. Wear And Tear

U-joints don’t always last forever. They wear out over time. This happens especially if you put a lot of strain on your u-joints on a regular basis. For example, towing or off-roading.

When a u-joint is subjected to high levels of strain for long periods of time, the metal components can become thin. They can also develop cracks. This reduces their ability to transfer torque properly, which is what causes u-joint failure.

Wear And Tear Due To High Loads

U-joints are designed to handle certain amounts of load. If you put more weight on your vehicle than it’s capable of carrying, your u-joints will have to work harder. This can lead to accelerated wear, which could result in failure after time.

Wear And Tear Due To Improper Installation

Proper installation is important for u-joint longevity. The caps and cups must be properly aligned to prevent damage. Also, make sure that your bolts are torqued down to their proper specifications.

3. Steeper Than Ideal Operating Angles

U-joints are designed to handle a certain amount of operating angle. If that limit is exceeded, the u-joints will wear out faster.

There are u-joints available for severe operating angles and there are standard u-joints for moderate angles. The more severe your operating angle is, the further you need to step up your u-joints. If you exceed the operating angles that these u-joints were designed for, they’ll struggle to handle their load. That will cause them to fail prematurely.

This is a common issue with lifted vehicles. The driveshaft operating angles become steeper if:

  • The vehicle is lifted
  • The pinion angles are incorrectly set

When operating angles are steep, excess vibration occurs. Vibration can damage the bearings. It can also damage the seals, which lets water and dirt in, and lets grease out.

Other Less Common Causes Of U-Joint Failure

There are a few other things that can cause u-joint failure, but they’re more rare. They include:

  • Over-torquing
  • Extreme use of the vehicle (racing, excessive towing, etc.)
  • Aggressive off-road driving
  • Heavily modified engines

Telltale Signs Of U-Joint Failure

Here are some telltale signs that the vehicle’s u-joints are failing:

  • Clunking noise when the vehicle starts to move forward or backward
  • Clunking noise when shifting from forward to reverse
  • Vibration felt throughout the vehicle when it is moving
  • Transmission or differential fluid leak

It’s Important To Find Out The Cause Of The U-Joint Failure

If you don’t fix the underlying issue that caused the u-joints to fail, the new u-joints will fail, too. Once you’ve determined the cause of the failure, the solution might be as simple as greasing your u-joints more often (if they’re not sealed). Otherwise, it may be necessary to address other issues like an out of balance driveshaft.

When u-joints fail, there’s a chance that the driver could lose control of the vehicle. If you suspect that they’ve failed, it’s important to replace them as soon as possible.


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