Why Are Two Universal Joints Required Whenever I Do A U-Joint Replacement?

Are you replacing a universal joint on your truck, SUV, or fleet vehicle anytime soon?It’s a good idea to get two replacement u-joints instead of one. It’s because you need to replace your u-joints in pairs, even if one of your u-joints has failed and the other one still looks fine. When one of your u-joints fails, the other one will fail soon.

How A Bad U-Joint Affects The Other One

old ujoint

U-joints are strong steel X-shaped parts with a single bearing cap at each end. The design of u-joints enables the driveshaft to rotate smoothly while connected to the differential and the transfer case (or transmission). They allow the driveline to flex with minimal friction.

When a u-joint fails, the driveshaft moves outside of its normal rotational path. This creates excessive vibration and friction. This not only further damages the failed u-joint, but it also damages the other u-joint. Both u-joints will undergo some damage, such as:

  • Loss of lubrication
  • Worn seals
  • Extreme wear and tear

All u-joints need lubrication. Grease allows the u-joint to move freely. The lubrication also protects the u-joint from corrosion and moisture. Over time, the u-joint begins to wear out, which results in increased friction inside the joint. The increased friction causes heat to build up in the u-joints. When this happens, the grease degrades. The u-joints lose lubrication and their seals wear out.

The first u-joint to fail has more damage than the second u-joint. So a lot of people think that the second u-joint is still fine. The truth is, the second u-joint is already starting to fail. So when you need to replace a u-joint, always replace the other one too. If you don’t, the other one will fail sooner or later. The failure of that u-joint will cause damage to the new u-joint (that replaced the first one). It’s always better to replace both u-joints at once.

Some Vehicles Have More Than Two U-Joints

multiple ujoints

Be sure to know how many u-joints your vehicle has. There are typically two u-joints to replace on either end of the drive shaft. Some driveshafts have a double-cardan joint at the front, which contains two u-joints. So there are three U-joints to replace. It’s best to replace them all at once.


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