Universal joints allow travel shafts to move up and down with the suspension while the shaft is usually moving so power could be transmitted when the drive shaft isn't in a direct line between the transmission and travel wheels.
Rear-wheel-drive vehicles currently have universal joints (or U-joints) at both ends of the travel shaft. U Joint china U-joints hook up to yokes that also allow travel shafts to move fore and aft as cars go over bumps or dips in the road, which effectively shortens or lengthens the shaft.
Front-drive vehicles also use two joints, called regular velocity (or CV) joints, however they are a numerous kind that also compensate for steering adjustments.
On rear-drive vehicles, one signal of a donned U-join is a “clank” sound whenever a drive gear is involved. On front-drive vehicles, CV joints sometimes make a clicking noise when they're worn. CV joints are covered by protective rubber footwear, and if the shoes or boots crack or are otherwise broken, the CV joints will lose their lubrication and be harmed by dirt and wetness.
A U-joint is found 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 teach some flexibility. This is necessary as all vehicles flex while in action.
U-joints are located on each of the ends of the rear travel shaft, whereas CV-joints are found on front wheel travel automobiles. Each allows the travel shaft to rotate as the differential movements in relation to the rest of drive train mounted on the chassis.
The U-joint 
functions to save wear and tear on your vehicle's transmission. Inability to get a universal joint substitute done when needed can cause substantial destruction to your car in the future.
There are some indicators that U-joint or CV-joint is failing. They involve:
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