Universal Joint

Universal joints allow drive shafts to move up and down with the suspension while the shaft is moving so power can be transmitted when the drive shaft isn’t in a straight line between the transmission and drive wheels. Rear-wheel-drive vehicles have universal joints (or U-joints) at both ends of the drive shaft. U-joints connect to yokes that also allow drive shafts to move fore and aft as vehicles go over bumps or dips in the road, which effectively shortens or lengthens the shaft.