Why change the cv axle of a car?

If the constant velocity (CV) joints are worn out they can become so sloppy that they can separate. When that happens, the remaining stump of the axle will turn into a flail and beat thousands of dollars of damage into your engine compartment.

Happily, your axle will give you a long period of advance notice before it utterly fails. When you have a few minutes, inspect the 'boots'. They are Accordion-like seals that hold in grease and keep out dirt. If your boot is ripped, a cheap replacement will save you having to replace the entire axle further on down the road.