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CV stands for constant velocity. The CV joints in cars are mean to ensure that power is delivered evenly to the wheels at all times, no matter what position the steering is in or how the car is riding on its suspension. Front wheel drive cars have CV joints on each side of the front half-axles.

The Boot

A CV joint on a car doesnt look like much. The actual joint where the motion occurs is enclosed in a rubber boot, a heavy, flexible rubber covering that encloses the entire joint. The boot serves two primary purposes. It constrains the grease that lubricates the joint that would otherwise drip or spin off the joint and keeps dirt that would make the joint sticky and ineffective out of the mechanism.

Ball Joints

Two types of ball CV joints are available. Fixed ball joints have a core called a "race" where six ball bearings sit. Those bearings are enclosed in a covering called a "cage" that allows them to roll freely. When the joint needs to move, the balls roll in their tracks in the inner race, allowing for the perfect transfer of power from the driveshaft to the wheel. Plunging ball joints operate on a similar principle but allow for more extreme angles.

Tripod Joints

Tripod joints are the other category of CV joints. Some car makers per tripod joints for the inner joints, while ball joints are used for the side of the axle that connects to the wheel. Instead of six points like a ball joint, a tripod joint uses three rolling points to provide its range of motion. These joints also move in and out based on the movement of the suspension.

Bearings

Inside a ball CV joint is a series of ball bearings that are kept lubricated and moving freely by the grease in the boot. Dirt, moisture and dust obstruct smooth motion of the bearings, which allows the joint to transfer power from all of the angles it may be delivered from. Tripod CV joints have rollers instead of ball bearings. These rollers are small and cylindrical and require the same type of enclosed lubrication as ball bearings.

CV joints, constant velocity joints, fit between the wheels and the drive shaft or transaxle of a car. The function of a CV joint is to allow a shaft to rotate over a flexible bend or angle without losing speed. An example would be where the steerable front wheels join to the cars axle in a front-wheel drive car.

Function

CV joints allow power to pass smoothly from the engine to the wheels without friction or play in motion. This is necessary because the front wheels of a car turn at different angles. CV joints cushion against up-and-down movements and allow wheels to be steered in front-wheel drive cars.

Compared to U Joint

U joints, or universal joints, also allow for rotation of a shaft over a bend. CV joints accommodate a wider range of angles without losing speed. For this reason, U joints are used mostly for wheels that are powered but not steerable, such as the back wheels in a rear-wheel drive car. However, CV joints are common in rear-wheel drive cars with independent suspension, where the left and right back wheels have greater independence of movement.

Types

There are two types of CV joint. The CV joint at the inboard end of the drive shaft is called a Triax joint. It adjusts for the up-and-down movement of the suspension. A second type of CV joint appears on the outboard end of the shaft, adjacent to the wheels. This joint is very flexible and allows wide range of movement in the front wheels.

Problems

Constant velocity joints are protected by a weather boot that keeps out moisture and dirt. If the boot is in good condition, joints are trouble-free. If the boot is damaged, the constant velocity joints are at risk. Check the boots condition regularly to prevent possible damage to the joints.

A CV joint is a flexible joint that transfers power to an automobiles wheel from the transmission. The CV joint is a collection of bearings that must be lubricated to resist wear to this vital part.

Lubrication Importance

The CV joints various moving parts are subject to large amounts of stress due to the automobiles movement. This stress can cause the part to wear prematurely, which can cause an expensive repair and present a safety hazard if the joint fails while driving.

Oil in CV Joint

Oil is not used as a lubricant for a CV joint in normal applications. The primary reason that oil is not used in CV joints is that the open bearings in the joint will not hold oil and the oil would simply drain away from the joint.

CV Joint Lubricant

Grease is used to lubricate CV joints, since grease will stay on open bearings and not simply drain from the area. The CV joint is covered with a rubber boot that prevents the grease from picking up outside contaminants and causing undue wear.