The universal joint is a coupling that connects two shafts and allows movement in all directions. This freedom of movement allows the drive shaft to move up and down as the car passes over bumps. Most rear wheel vehicles will need the u-joint replaced at least once during their service life and more often if the vehicle is high performance or has a manual transmission. The life of the u-joint can be extended by servicing it regularly with the proper lubricants; however, popping the clutch and full throttle power shifting will shorten the life of the u-joint considerably.
Drive the vehicle onto dual ramps or have the car raised to gain easier access to the underside of the car for inspection of the u-joint.
Inspect the u-joints visually to ensure the welds are not cracked, the balance weights are not missing and there is no mud coating the u-joint. Spray or clean any mud from the u-joint. Replace the balance weights or re-weld any cracked welds. All of these issues can create a vibration while driving but does not necessarily mean it is the u-joint.
Grasp either side of the u-joint and rotate it back and forth while watching for any play between the cross and the yolk. If the cross moves inside the yolk, replacement of the u-joint is warranted.
