All 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 and the outer CV joints connect the drive wheels to the drive shafts (see the picture). Many rear- and four-wheel drive cars and trucks have CV joints as well. The CV joints are needed to transfer the torque at a constant speed to the steered wheels as well as to accommodate up and down motion of the suspension.
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.
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 shaft, while the tripod-type CV joints mostly used on the inner side.
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.
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 the drive wheel, around the area where the CV joint is. If you take your car to a repair shop regularly, a mechanic can spot the problem and let you know.
If a damaged CV joint boot caught early, simply replacing the boot and repacking the CV joint with fresh grease may fix the problem. If the car continues to be driven with a broken CV joint boot, the CV joint or a whole drive shaft will need to be replaced. In worst cases, a badly-worn CV joint can even disintegrate while driving causing the vehicle to stop. A most common symptom of a badly-worn CV joint is a clicking or popping noise when turning.