Universal joints allow drive shafts to move up and down with the suspension while the shaft can be moving so power could be transmitted when the drive shaft isn’t in a directly line between your transmission and drive wheels.
Rear-wheel-drive vehicles include universal joints (or U-joints) at both ends of the travel shaft. U-joints connect to yokes that also allow travel shafts to go fore and aft as automobiles review bumps or dips in the street, which effectively shortens or lengthens the shaft.
Front-drive vehicles also work with two joints, called regular velocity (or CV) joints, but they are a distinct kind that also compensate for steering improvements.
On rear-travel vehicles, one indication of a donned U-join is a “clank” sound when a drive gear is involved. On front-drive cars, CV joints generally make a clicking sound when they’re donned. CV joints are covered 
by protective rubber boot footwear, and if the U Joint footwear crack or are or else broken, the CV joints will lose their lubrication and be damaged by dirt and moisture.
A U-joint is found in both front wheel travel and rear wheel drive cars. Although they are different in design, they possess the same purpose of giving the drive teach some flexibility. This is necessary as all cars and trucks flex while in action.
U-joints are located on each one of the ends of the trunk drive shaft, whereas CV-joints are located on front wheel drive automobiles. Each allows the drive 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 vehicle’s transmission. Inability to have a universal joint substitute done when necessary can result in substantial damage to your vehicle in the future.
There are several warning signs that U-joint or CV-joint is failing. They contain: