On rear-wheel-drive vehicles, universal joints allow the driveshaft to transfer torque at different angles as the vehicle travels over bumps in the road.
If worn, they cause a clunk when the transmission is placed into drive or reverse. They also cause driveline vibrations that increase with vehicle speed.
A U-joint consists of the spider joint, four caps, and their retaining clips. Each cap contains needle bearings that allow for high-speed operation, held in place with thick grease. As the joint wears, it can become loose and lose vital lubrication.