CV Joint

~Function~
All front-wheel drive cars have Constant Velocity joints or CV joints on both ends of the drive shafts. Inner CV joints connect the drive shafts to the transmission, while the outer CV joints connect the drive shafts to the wheels. Many rear-wheel drive and four-wheel drive cars as well as 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, CV joints 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. In front-wheel drive cars, ball-type CV joints are used on the outer side of the drive shafts (outer CV joints), while the tripod-type CV joints mostly used on the inner side (inner CV joints).

Constant-velocity joints (CV joints) allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive vehicles, and many modern rear wheel drive cars with independent rear suspension typically use CV joints at the ends of the rear axle half shafts and increasingly use them on the prop shafts (drive shafts).

Constant-velocity joints are protected by a rubber boot, a CV gaiter, usually filled with molybdenum disulfide grease. Cracks and splits in the boot will allow contaminants in, which would cause the joint to wear quickly. CV joints often connect two intersecting, rotating shafts that make an angle with one another, especially when this angle regularly varies in service. A common example is found in front wheel-drive cars at the connection of a half-axle with a front wheel, where the CV joint ensures even torque transmission when the wheel moves due to steering. Another example is found in rear wheel-drive cars with independent rear suspensions where the rear axle half-shafts connect with the rear wheels.

A CV joint is an assembly of bearings and cages that allows for axle rotation and power transmission at a number of different angles. CV joints consist of a cage, balls, and inner raceway encased in a housing covered by a rubber boot, all of which is filled with lubricating grease. The grease is necessary to reduce the friction of all the spinning parts of the CV joint. Cracks in the boot will allow in contaminants, which can cause heat due to friction and cause the joint to wear quickly.

If a car is continued to be driven with a damaged CV joint boot, the CV joint will wear out and eventually fail. A 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. In worst cases, a badly-worn outer CV joint can even disintegrate while driving. This will make your car undriveable. Inner CV joints failures are rare. One of the symptoms of a failed inner CV joint is shudder or side-to-side shake during acceleration. A worn-out inner CV joint may also cause clunking when shifting from Drive to Reverse.

TOP