How Does a Constant Velocity Boot Work?

1. A constant velocity boot, or a CV boot, is a piece of rubber that protects
   the joint of a constant velocity axle (CV axle). There are usually two joints on a CV axle--the inner joint and the outer joint. CV axles are found on front wheel drive cars and transfer power from the transmission to the wheels.
2. The constant velocity book slips on over the inner and outer joints, protecting the joints from dirt and road grime. Sometimes, depending on the year, make and model of the car, the boot slides on over the end of the axle. Sometimes the boot is a two-piece boot that is strapped onto the axle. There is grease inside the joints to keep them working well, and the constant velocity boot keeps any grease that may sling off the joint from slinging onto the car.
3. When a boot tears or cracks, it allows the grease from the CV joint to be thrown on the bottom of the car. Wind speed can sling the grease quite far back. It then sticks to the car and attracts more dirt and road grime. It also helps to keep the grease in the joint. A cracked or torn boot will allow dirt and road grime to penetrate the joint, which reduces the life of the joint.
   Once the joint goes bad, the axle must be replaced. You can tell when an outer axle joint is bad; it will click when turning left or right. If the inner joint is bad, you will hear it clicking while moving straight. It is not often that an inner joint goes bad but quite common for outer joints to go bad. It is also common for the outer boots to crack or tear, since they put up with a lot more movement than the inner boots.
4. If you notice a crack or tear in the CV boot, get it replaced as soon as
   possible. Spending the money replacing the boot could extend the life of the axle, which is a more expensive repair. If an axle seizes up, there is the slim possibility that you could damage the transmission or the wheel hub.

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