Universal joints allow travel shafts to move up and down with the suspension while the shaft 
is moving so power could be transmitted when the drive shaft isn't in a straight line between the transmission and drive wheels.
Rear-wheel-drive vehicles own universal joints (or U-joints) at both ends of the drive shaft. U-joints hook up to yokes that likewise allow drive shafts to go fore and aft as cars review bumps or dips in the road, which efficiently shortens or lengthens the shaft.
Front-drive vehicles also use two joints, called regular velocity (or CV) joints, but they are a diverse kind that also compensate for steering adjustments.
On rear-drive vehicles, one signal of a put on U-join is a “clank” sound whenever a drive gear is U Joint engaged. On front-drive cars, CV joints sometimes make a clicking noises when they're put on. CV joints are covered by protective rubber shoes, and if the shoes crack or are or else damaged, the CV joints will eventually lose their lubrication and be destroyed by dirt and moisture.
A U-joint is situated in both front wheel drive and rear wheel drive cars. Although they are different in design, they have the same reason for giving the drive train some flexibility. That is required as all cars and trucks flex while in motion.
U-joints are located on each one of the ends of the rear travel shaft, whereas CV-joints are found on front wheel drive autos. Each allows the travel shaft to rotate as the differential moves in relation to the others of drive train attached on the chassis.
The U-joint functions to save wear and tear on your own vehicle's transmission. Failing to possess a universal joint replacement done when required can result in substantial damage to your vehicle in the future.
There are many warning signs that U-joint or CV-joint is failing. They consist of: