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CV Joint Replacement Tips

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Constant velocity (CV) joints have been around since the 1980s when front wheel drive (FWD) became mainstream.

Although some rear wheel drive (RWD) and all wheel drive (AWD) vehicles also use CV joints, most are found on FWD cars and minivans. CV joints are used in place of U-joints because they allow the joint to bend at a wider angle without inducing drivetrain vibration. When a U-joint operates at an angle of more than a few degrees, it varies the speed of the shaft.

The larger the angle, the greater the cyclic vibrations. Depending on the application, CV joints can withstand joint angles of up to 47 to 54 degrees without these vibrations. Various types of CV joints are used, but most outer joints are of the Rzeppa design with six balls that roll in races between the inner and outer joint housing. As the joint bends, the balls always bisect the angle of the joint, rotating in a plane that is half the angle of the joint.

A steel cage holds the balls in position. Over time, cage windows can wear out, allowing balls to rattle and pop when the vehicle is steered left or right. This produces a rattling or popping noise that is a classic symptom of a worn CV joint. Wear or damage in the ball grooves or on the polished balls can also produce noise and play in the seal. CV joints are lubricated with a special grease for high temperature CV joints, similar to wheel bearing grease.

Gaskets can last a long time, as long as the protective rubber or plastic sheath that surrounds the gasket remains intact and does not leak. The #1 cause of premature CV joint failure is usually a torn, cracked, or leaking boot. Even a small pinhole or hairline crack will allow grease to be lost from the seal due to the centrifugal force generated by the rotating seal. Loose, broken or missing boot clips can also allow the boot to leak. Dirt and water can also penetrate a leaky boot and cause wear and corrosion.

By the time the leaking boot is discovered, many CV joints are severely contaminated or worn and need to be replaced. The CV joints and boots can be replaced individually, but most professional technicians and even DIYers prefer to replace the entire half shaft with a remanufactured one. Reman trees are pre-assembled and ready to install. Some shafts have new CV joints, while others have ground joints with oversized balls.

Either way, a rebuilt shaft is a much faster, easier, and less messy way to replace a failed CV boot or CV joint. There is also less chance of installation errors and returns with a pre-assembled tree. On a high mileage vehicle with a bad CV joint or boot, it’s often a good idea to replace both shafts at the same time. Often the right shaft (passenger side) fails first because right turns are at a steeper angle than left turns, and right turns are more common than left turns. Therefore, the right outer CV joint and boot are the first to go. Special tools that may be required to replace a shaft include a hub puller to separate the outer CV joint from the steering knuckle and wheel bearing, and/or a hydraulic press for older Asian vehicle applications with interference fit wheel bearings.

Seals

One mistake technicians make when installing a new axle or driveshaft is not treating the joints of the transmission, differential, or transfer case.

Most seals ride on a shaft and usually have a lip and a spring that hold the lip to the axle. When a seal is installed, take your time installing the axle. Splines can damage the seal and cause leaks.

The area of ​​the shaft where the seal and the bearings come into contact is the most important. It should be free of all rust and blemishes. Use only fine emery paper to clean the axle shaft between the flange and the worn area.

If the surface is gouged or damaged, the axle can be repaired with a sleeve on some applications. If not, the axle must be replaced. Make sure the gasket is installed in the correct position.

Breathers

Make sure the breathers are not clogged. The breather acts like a PCV valve to keep the pressures within a certain range so the seals can work best as the differential heats up and cools down. If a breather is clogged, the temperature will increase the pressure in the axle. As the transmission cools, negative pressure can build up behind the seal. These pressure changes will cause the seal lips to warp and leak.

It is important to note that any axle leak should be taken seriously. Ignoring a leak can be very expensive as it can destroy the bearings, brakes and differential.