CV Joint, how it works, symptoms, problems

Updated: August 4, 2013
CV Joints
CV Joints in a front-wheel drive vehicle.
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CV Joint boot looks OK
The CV joint boot looks OK.
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CV Joint boot looks OK
Trucks have CV joints too.
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Broken CV boot
Broken CV joint boot.
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Broken CV boot
The hub nut.
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All front-wheel drive cars have Constant Velocity joints or CV joints on both ends of the drive shafts (half shafts).
Inner CV joints connect the drive shafts to the transmission, while the outer CV joints connect the drive shafts to the drive wheels (see the picture). Many rear- and four-wheel drive cars and trucks also have CV joints.

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, the CV joints also have to be able to deliver the torque to the front wheels during turns.

There are two most commonly used types of CV joints: a ball-type and a tripod-type. Ball-type CV joints are commonly used on the outer side of the drive shafts, while the tripod-type CV joints mostly used on the inner side of the drive shafts in front-wheel drive cars.

A CV joint is packed with a grease and sealed tight by the rubber or plastic boot. A CV joint doesn't need any maintenance and can last very long, as long as the protective CV joint boot is not damaged.

A most common problem with the CV joints is when the protective boot gets damaged. Once this happens, the grease comes out and the moisture and dirt come in, causing the CV joint to wear faster and eventually fail due to lack of lubrication and corrosion. Usually the outer CV joint boot breaks first, as it has to endure more movement than the inner one.

One of the early signs of a broken CV joint boot is a dark grease splattered on the inner side of the rims and around the inside of a drive wheel; around the area where the CV joint is located. If you take your car for a maintenance to a repair shop regularly, your mechanic can spot the problem early and let you know. Sometimes you can see the cracks and signs of wear on the boots before they break.

If a damaged CV joint boot caught early, simply replacing the boot and repacking the CV joint with a fresh grease is all that is usually needed to fix the problem. If the car is continued to be driven with a damaged CV joint boot, the CV joint will eventually fail. A most common symptom of a badly-worn CV joint is a clicking or popping noise when turning. Usually the noise gets louder when accelerating in turns.
In worst cases, a badly-worn CV joint can even disintegrate while driving causing the vehicle to stop; I've seen this happening few times.
A damaged CV joint is not repairable. It will have to be replaced with a new or a reconditioned part. Sometimes, the CV joint does not come separately. In this case, the whole drive shaft will usually need to be replaced. The drive shaft replacement cost could vary from $300 to $800 in a repair shop. The CV-joint boot replacement could range from $200 to $700, even though the rubber boot itself usually costs around $20-$30. This is because of the large amount of labour involved.

If you are planning to replace the CV joint boot or a drive shaft yourself, beside the regular tools you are going to need a strong torque wrench or a breaker bar to break loose the main CV joint lock-nut or hub nut, because it's very tight (the lower photo). The last time I replaced the CV joint boot at home I actually broke my breaker bar - the hub nut is very tight. It will also have to be re-torqued to the specified torque after the repair is completed. Check the repair manual for instructions and torque specifications. A typical repair procedure also involves disconnecting one or two ball joints. In my car I had to use a special tool to separate a ball joint stud from the steering knuckle.

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