U-Joint

📖 YOUCANIC Automotive Glossary

A U-joint (Universal Joint or Cardan joint) is a cross-shaped coupling that connects driveshaft sections on RWD and 4WD vehicles, allowing the driveshaft to transmit power at an angle between the transmission output and the rear differential input. The U-joint accommodates the changing angle as the rear axle moves through suspension travel. Most driveshafts have two U-joints (front and rear), and some two-piece driveshafts have a center support bearing with additional U-joints.

U-joint failure produces vibration at highway speed (worn but not seized), clunking during direction changes (excessive play), or driveshaft separation in extreme cases. Test by grabbing the driveshaft near each U-joint and checking for any play — even slight movement means replacement. U-joints are an inexpensive maintenance item but catastrophic if ignored. Many modern vehicles use sealed U-joints that cannot be greased — when they fail, replacement is the only option.