Car Parts – What is a CV Joint?

CV JointAll front-wheel drive cars have Constant Velocity joints or CV joints on both ends of the drive shafts (half shafts).
The inner CV joints connect the drive shafts to the transmission, while the outer joint connects the drive shafts to the wheels. CV joints can also be found of many rear wheel drive and all wheel drive vehicles as well.

What does it do?
The CV joints are needed to transfer the torque from the transmission to the drive wheels at a constant speed, while accommodating the up-and-down motion of the suspension. In front-wheel drive cars, CV joints deliver the torque to the front wheels during turns.

Where is it located?
The CV joints are located under the vehicle, connecting the wheel to the transmission.  This can be seen in the illustration below. Although every car is a little different, this is one part that is pretty much the same in every vehicle.

cv location

CV-joint problems

CV Joint boot looks OK

This is what a normal CV-Joint should look like.

Because there are moving parts in a CV-joint, normal wear and tear is going to happen.  When problems occur, the evidence is usually quite easy to see.  A CV joint is packed with a special grease and sealed tight with the rubber or plastic boot, that is held in place with two clamps. When there is damage to the rubber or plastic boot, a service technician should easily detect it. Unless there is damage to the boot, the CV-joint typically does not need to be replaced.  Many times you can see an intact CV-Joint on a car with 200,000 miles and still have the original part.  Most damage to CV-Joints occur when a vehicle is subject to rough roads, impact with debris, or a little off-roading.  When the boot gets cracked or damaged, the grease inside will ooze out which will cause the CV-joint to wear down faster and eventually fail due to lack of lubrication and corrosion. Usually outer CV-joint boots break first, as they have to endure more movement than the inner ones.

cvjointdiagram

Signs of a damaged CV-joint boot or worn CV joint

Broken CV boot

Grease coming out of a small crack or tear is the early sign of the CV joint boot failing. If the damage is bigger, you might see dark grease splattered on the inside of the wheel rim and around the area inside of the drive wheel like in the photo. If you continue to drive on a worn out CV-Joint, the joint will eventually fail and the car will be non-drivable.  Although a worn CV-Joint can last for a little while, it is best advised to replace it as soon as possible.  How can you tell if you CV-Joint is failing or damaged without getting under your vehicle? The most common symptom of a badly-worn outer CV joint is a clicking or popping noise when turning. Usually the noise gets louder when accelerating in turns. One of the symptoms of a failed inner CV-joint is shudder or side-to-side shake during acceleration. Another indicator of a worn-out inner CV joint may also cause clunking when shifting from Drive to Reverse.

Fix or Replace?

Although it is cheaper to just fix the boot on a CV-Joint, the added cost to replace the whole  joint and axel may not cost much more than  just the boot itself because of the labor time involved.  Most repair facilities will recommend that you just replace the whole thing. This will ensure that all the parts are working and there isn’t anything that is missed when just repairing the boot.

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