Universal Joint (U-Joint)
A mechanical linkage in a driveshaft assembly that allows power transmission at varying angles, accommodating suspension movement.
A Universal Joint (commonly called a U-joint) is a mechanical connection that allows a rigid rotating shaft to bend or pivot while transmitting rotational force. U-joints are standard components in rear-wheel-drive, four-wheel-drive, and all-wheel-drive vehicles, positioned at either end of the drive shaft to connect it to the transmission, transfer case, and differential.
As the vehicle's wheels move up and down over road bumps, the angle between the transmission and the rear axle changes continuously. The U-joint, consisting of a cross-shaped pivot journal and needle bearing cups, allows the drive shaft to spin smoothly while flexing under these shifting angles.
U-joints can wear out due to loss of lubrication, water intrusion, or heavy towing loads. Common signs of a failing U-joint include a loud clunking noise when shifting from reverse to drive, squeaking noises that vary with vehicle speed, or a severe drivetrain vibration felt through the floor. Failing to replace a worn U-joint can result in the driveshaft detaching completely, causing major damage and safety hazards.