CV Joints: its function, faults and fixes!

Purpose and function of CV Joints:

All front-wheel drive cars, many rear wheel drive cars as well as trucks have Constant Velocity joints or CV joints on both ends of the drive shafts (half 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 purpose of CV Joints is to transfer the torque (power) from the transmission to the drive wheels at a constant speed, while accommodating the up-and-down motion of the suspension so that the vehicle may move forward. 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 are mostly used on the inner side (inner CV joints.



CV Joint problems

A CV joint is packed with special grease and sealed tight with a rubber or plastic boot that is held in place with two clamps. The grease and plastic boot protects it form dirt and debris. A CV joint doesn't need any maintenance and can last very long, as long as the protective CV joint boot is not damaged. Because the CV axles are the direct link that transfers the power of the engine to the wheels, they are subject to high levels of stress over time and will however eventually wear out and require replacement for proper functionality to return.

The most common problem with CV joints is when the protective boot cracks or gets damaged. Once this happens, the grease comes out and moisture and dirt get in, causing the CV joint to wear faster and eventually fail due to lack of lubrication and corrosion. Usually outer CV-joint boots break first, as they have to endure more movement than the inner ones. CV boots are typically inspected during regular maintenance visits. Your mechanic will look for cracks, tears and other damage.


Identifying a damaged or worn out CV Joint

Grease coming out of a small crack or tear is an early sign of the CV joint boot failing. If the damage is larger, you might see dark grease splattered on the inside of the wheel rim and around the area inside of the drive wheel. If the car continues to be driven with a damaged CV joint boot, the CV joint will wear out and eventually fail.

The most common symptom of a worn outer CV joint is a clicking or popping noise when turning. The clicks may become louder or more pronounced during sharper and faster turns, and will be heard on the side with the faulty CV shaft. In the worst cases, a badly-worn outer CV joint can even disintegrate while driving, which could create a potentially hazardous situation.

Inner CV joint failures are rare. One of the symptoms of a failed inner CV joint is excessive lateral (side-to-side) shaking or vibration during acceleration. If a CV joint or axle shaft is damaged in any way that affects its balance while rotating, it will cause the shaft to vibrate excessively while operating the vehicle. The vibrations may oscillate, or become more pronounced as vehicle speed increases. Excessive vibration from failing CV shafts can interfere with handling and ride characteristics, and the overall safety and comfort of the vehicle. A worn-out inner CV joint may also cause clunking when shifting from Drive to Reverse or from accelerating to decelerating and need to be replaced if it is damaged enough to cause vibrations. 


Repairing CV Joints

If a damaged CV joint boot is caught early, simply replacing the boot and repacking the CV joint with fresh grease is all that is usually needed. This is much cheaper than replacing the whole CV joint or drive shaft.  The part is usually not very expensive, but a fair amount of labor is involved to replace it. The CV joint boot is typically sold as a kit with fresh grease and new clamps. If a CV joint itself is worn out, it cannot be repaired; it will have to be replaced with a new or reconditioned part. Sometimes, a CV joint does not come separately. In this case, the whole drive shaft will need to be replaced. 

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Posted on Sep 22, 2020 by Auto Repair Directory

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