Part Profile: CV Joint

cv joint sketch

This is the first of our part profile series. The idea is to give everyday drivers more information on important parts of their vehicles. You can understand your entire vehicle, one part at a time.

The constant velocity joint or CV joint provides a form of mechanical coupling in which the rotational speed of input and output shaft remains the same no matter what the operating angle of the joint.

The CV joint is located at the axel and allows the job shafit to accomplish it’s two most important jobs. That is, transmit power to the wheels and adjust to the suspension. As the suspension of the vehicle changes due to road conditions, the CV joint allows continued transfer of power. This gets even more complicated in the case of front wheel drive vehicles where articulation angles are higher because of steerable wheels. With the wide range of variable angles by suspension travel and wheel steering, the axle has to act flexibly. Thus, the vehicle employs inboard and outboard CV joints to permit the torque through a wide array of angles.

In rear-wheel drive applications, operating angles are much lower and less stress is placed on the CV joint as a result.


A dusty dirty CV joint.

CV Joint Problems

A CV joint is a collection of many components (bearings, race, cage, housing and balls) connected together in a precisely fitted assembly. All the parts spin around in a protective layer of special grease which is held inside the joint assembly. The assembly is packed and sealed tight with flexible rubber boot held in place by clamps and prevents the grease coming out of the CV joint. The boot also keeps the joint safe from outside contamination and keeps dirt and grime out. A CV joint doesn’t require any kind of regular maintenance and can perform very long if the rubber boot is not damaged. Over time, rubber boots fail from age or can become cracked, torn by road debris.
The most common problem with the CV joint is damaged boots. Once the boots get damaged, grease makes its way out and moisture and dirt get into the CV joint assembly. This will ruin the CV joint by causing it to wear out faster and fail eventually. Outer CV joints boots fail earlier than inner ones as they have to endure more strains due to more angles.

Signs of a failing CV Joint

CV joints may fail as a result of a lack of lubrication or the introduction of contamination. In extreme cases, a badly worn CV joint can disintegrate while driving leaving a vehicle undrivable. Most often, a failing CV joint will cause a loud clicking noise while turning. To confirm, crank the steering wheel to one side and drive around in circles either backwards or frontwards. If the noise gets louder  then you can feel pretty confident that you’re dealing with a CV joint issue.

Don’t waste time putting off repair of this one. You will either end up with an undrivable vehicle or as if often the case, a much higher repair bill when you have to fix the vehicle axels.


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