Glossary of Automotive Components/Terms

CV Joint/Boot

CV stands for Constant Velocity.  These joints are mostly found on front wheel drive, 4 wheel drive, or rear engine cars, but can be found on some luxury rear wheel drive cars. They allow a driveshaft  to propel the wheel smoothly at the sharp angles caused by front wheels being turned right and left, and up and down  suspension movements. CV joints are similar to a universal joint (U-joint) except they will compensate for much higher angles.

CV Boot. A rubber accordion cone shaped boot that goes around a CV axle joint. The boot holds in lubricant to keep the joint from overheating and keeps dirt and moisture out of the bearings.
As the rubber in the boots age they begin to crack, especially the outer boot which flexes more. When the cracks get deep enough the boot splits, throws out the lubricant and allows dirt and moisture in. The axle joint fails soon after this.

CV boot                                  CV joint
  CV Joint with Boot                                    CV Joint without boot.