U-Joints

In order to transmit power when the drive shaft is not in a straight line between the gearbox and drive wheels, universal joints allow drive shafts to move up and down with the suspension while the shaft is moving. At both ends of the drive shaft of rear-wheel-drive cars are universal joints, sometimes known as U-joints. When a vehicle travels over bumps or dips in the road, U-joints connected to yokes also allow drive shafts to move fore and aft, thereby shortening or lengthening the shaft.