What Is A CV Joint?

What Is A CV Joint

We all typically take our vehicles for granted until something goes wrong. Then we need to rely on a mechanic to tell us what the problem is and to fix it.

That’s why it’s important to be familiar with the most important parts of your vehicle. Like a CV joint. But what is a CV joint? 

We’ll take you through what it is, how it works and what to look out for if it is starting to fail. 

What Is A CV Joint?

A CV joint is a constant velocity joint. It connects two parts of the driveshafts of a vehicle and are essential to joining the driveshafts to the transmission and the wheels (see also ‘How To Measure Wheelbase‘).

The inner CV joint connects the driveshafts to the vehicle’s transmission and the outer CV joint connects the driveshafts to the vehicle’s wheels. 

All front-wheel drive vehicles have a constant velocity joint although some four-wheel drive and rear-wheel drive cars and trucks have CV joints too (see also ‘What Is A Transfer Case?‘).

The two most common types of CV joint are a tripod type and a ball type. Ball types are used on the outside of the driveshafts, these are called outer CV joints. Tripod types are more often used on the inside which is why they are called inner CV joints. 

The CV joint that is most commonly used is the Rzeppa named after the man who invented it in 1926.

Due to its design this joint can accommodate large changes in angle when the front wheels are turned. They typically allow 45-48 degrees of articulation, although some give up to 54 degrees. 

How Does It Work?

CV joints are essential for transferring the torque from the transmission to the drive wheels at an even and constant speed. It has to do this while also making allowances for the up and down movement of the suspension and to articulate over uneven road surfaces. 

A CV joint has to allow the transmission of power through a wide range of angles all while ensuring minimum friction and internal play. The inside of a CV joint is filled with a dark green or gray specialized grease for lubrication. 

Over the CV joint is the CV boot. This is a neoprene or rubber flexible protection designed to keep the grease in the joint and the moving parts coated. It also prevents dirt and debris getting into the CV joint. 

Unfortunately, the boot is the weakest part of the CV joint. Following years of moving, turning and the up and down movement of the suspension, the boot can begin to weaken and eventually break.

CV Joint Problems

As we have seen, the biggest and most frequent problem with CV joints is the failure of the boot. Once this has torn it no longer keeps the grease on the joint and the moving parts will no longer be coated in grease for protection and lubrication. 

The lack of lubrication will allow contaminants to build up in the joint and cause friction. This will accelerate the wear on the internal parts of the joint and will cause play in it. 

With the boot torn there is also nothing to prevent road dirt and debris from getting into the CV joint which causes further degradation and damage. Water can also penetrate the CV joint and without the protective coating of grease the joint is subject to rust. 

What Is A CV Joint (1)

Signs Of Damaged CV Joint

When a CV joint has failed you may hear a loud clicking sound when slowly accelerating and when turning your car. A visual inspection will typically show the physical damage to the CV boot such as a crack or tear. 

Another, perhaps more obvious sign of a damaged CV joint is the presence of the grease that should be encompassed by the boot around the joint, on other internal components of the engine. 

This is because the tear in the boot is allowing the CV joint to throw out the lubricating grease. 

Failure of the inner CV joint is rare but can happen. The signs of this problem are vibration or side to side shaking on acceleration. If an inner CV joint is worn out it may cause a clunking sensation when shifting gear from Drive to Reverse or when decelerating. 

CV Joint Repair

If you are unfortunate enough to have a failed or damaged CV joint, what is the solution? 

When the problem is detected early enough it is possible to simply replace the boot and repack the CV joint with grease.

It is a much cheaper process than needing to replace the whole CV joint and why regular maintenance and checks are worthwhile. 

Cost Of CV Joint Repair

By using preventative maintenance you can save yourself an expensive trip to your mechanic. 

Replacing a CV boot will cost on average between $180 and $350. The part itself is not expensive, but there is a lot of work involved in replacing it, so it is mostly labor charges. A new CV joint boot is usually sold as a kit with new clamps and fresh grease. 

If the inner CV joint is worn out it cannot be fixed and will need to be replaced. You can either do this with a new part or to save some money, with a reconditioned CV joint.

Occasionally, a CV joint cannot be replaced separately and in this instance the whole shaft will have to be replaced. If this is the case you may be faced with a cost of between $380 and $800 for the work. 

Some people may be able to change CV joints themselves with the right tools but if you are not 100% sure of what it involves it is best to leave it to a professional mechanic. 

Final Thoughts

Preventative maintenance is always the best approach for any vehicle.

With some knowledge of the things that can go wrong with your car you can tackle issues before they become bigger problems. We hope you have enjoyed our guide to CV joints. 

Dave Oliver

Dave Oliver is a seasoned car modification expert with over twenty years of experience in the field. His knowledge spans from restoring vintage models to implementing the latest customization technologies. He brings his passion and expertise to life through informative and engaging articles.

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