CV Boot
A flexible protective rubber or plastic boot that covers a constant velocity (CV) joint, keeping grease in and dirt out.
A CV boot (constant velocity boot) is an accordion-style protective sleeve made of rubber or high-strength thermoplastic. It is clamped over the CV joints on a vehicle's CV axles, which are commonly found on front-wheel-drive and all-wheel-drive vehicles.
The CV boot serves two critical functions: it seals in the specialized high-temp grease that lubricates the precision bearings inside the CV joint, and it seals out road dirt, water, sand, and salt that would quickly destroy the polished metal surfaces of the joint.
Because CV boots flex constantly as the wheels steer and move up and down with the suspension, they are prone to wearing out. Over time, the rubber can dry rot, crack, or be torn by road debris. Once a boot splits, centrifugal force throws the grease out, and dirt enters, causing rapid wear of the CV joint.
The classic sign of a torn CV boot is grease splattered on the inside of the wheel or steering components. Catching a torn boot early allows a mechanic to repack the joint with grease and install a new boot, saving the expense of replacing the entire CV axle.