The Importance of CV Joint Boot Replacement

Constant velocity (CV) joints are located on the drive axles of front wheel drive vehicles. These drive axles, commonly called half shafts, and bolt to the transaxle, which is the interface between the transmission. This is similar to a differential on a rear-wheel drive car. The opposite end of the half shaft slips into a spline on the wheel hub, and is secured in place with a nut and cotter key. There is a half shaft for both front wheels and each half shaft has two CV joints. One CV joint is located on the transaxle side of the half shaft while the other CV joint is positioned near the wheel. CV joint boots cover all four CV joints on a front-wheel drive car or truck. When the CV joint boots go bad, the entire movement of the car is affected, and these parts should be replaced immediately.

What Function Does a CV Joint Perform?

The CV joint is constructed with large ball bearings that allow the joint to flex up and down or side to side while the vehicle is moving. The CV joints on the end of the half shafts spin when power is applied to the wheels through the axles. The flexing of the CV joints allows the wheel to be turned left or right while the shaft is spinning, and also allows the wheel to move up and down when responding to road shocks.

What Function Does the CV Joint Boot Perform?

To prevent the CV joint from wearing as the ball bearings move within their sockets the joint is packed with grease. The CV joint boot surrounds the joint to keep the grease from being flung out when the joint spins. The boot is a round sleeve that when set on end appears to form a pyramid shape with rounded sides. The top of the pyramid has a small hole that the axle shaft slips through, and a large hole on the opposite end, or the base of the pyramid, fits over the housing of the CV joint. The boot is held in place with a clap around both ends.

What Happens When a CV Joint Boot Fails?

Failure of a CV joint boot generally occurs when the rubber boot splits, allowing the grease trapped inside to be slung out. The rubber seals are not repairable, and must be replaced. CV joint boot replacement involves removing the half shaft from the car, disassembling the CV joint and removing the damaged boot, slipping a new boot into place, and clamping the ends of the boot to hold it securely in place.

What are the Symptoms of CV Joint Boot Failure?

Outer CV joint boots fail far more frequently than the inner joint boots close to the transaxle. When the boot cracks or splits, grease is sprayed along the inside of the tire, and will occasionally drip from the boot or the wheel onto the surface where the vehicle is parked. As the grease continues to be expelled from the joint, the driver may hear a clattering noise on turns that is coming from the joint itself. This clattering noise is produced by the ball bearings rattling in the joint housing as the joint flexes and spins during the vehicles turning motion.

Does the Clattering Noise Damage the Ball Bearing or the CV Joint Itself?

If the clattering noise is the first symptom the driver has noticed then most of the grease is already gone from the joint and damage can occur rapidly. The boot should be replaced as soon as possible to prevent damage to the CV joint. Driving the vehicle on an almost dry CV joint will damage the joint, and may necessitate replacing the half shaft on the side of the vehicle with the broken boot.

A CV joint boot replacement can be done fairly quickly by a certified technician with the proper tools. The replacement of a CV joint boot should not be attempted by novice technician as there is the potential to damage component parts or the vehicle if the repair is not performed properly. Replacement of a CV boot is somewhat costly repair, but far less expensive that replacing the entire half shaft. Prompt attention to a torn CV joint boot can eliminate the need to replace a joint, or the entire assembly due to lack of proper lubrication.