Front-wheel vehicles, many all-wheel vehicles and some rear-wheel vehicles have constant-velocity joints, also known as CV joints, that connect the transmission to the drive axles and wheels. A front-wheel car will have four CV joints, each covered by a boot.
Related: More Maintenance Coverage
CV joints are covered by rubber or plastic boots. Known as a CV boot or drive axle boot, these parts are responsible for keeping the joints lubricated and preventing dirt and water from getting in. Unfortunately, this is a part that sometimes fails. If a CV boot tears, grease can leak out and moisture and dirt can get in. If left unattended, it’s only a matter of time before the joint fails from lack of lubrication or corrosion. When that happens, the whole axle may need to be replaced.
CV axle boots often last the life of a vehicle and are not listed among items that need periodic replacement as part of vehicle maintenance. They should, however, be inspected at least once a year, or more often on high-mileage vehicles or ones that see what manufacturers describe as “severe” service, such as off-road use or transportation-industry conditions. Since outer boots are more prone to tears, it is especially important to check these parts.
Replacing a CV Boot
It is possible to drive a car with a torn CV boot, but doing so will likely lead to further damage that will eventually require more extensive repair. If a small tear in a CV boot is caught early, it may require only the relatively minor repair of replacing the boot and adding fresh grease instead of more major surgery. Many repair shops, though, will recommend replacing the entire axle if a boot is torn because there may be unseen damage to the CV joints, axle shafts and other parts that could result in other problems.
Outer boots (the ones closest to a wheel) are more prone to tears than inner boots. One indication of a torn boot is grease spots under the front axle or grease splattered on or around the inward-facing side of a wheel. Among the indications that a CV joint or axle has been damaged is a clicking or popping noise when turning, or vibrations at highway speeds.
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