What is a CV joint and why do they break?

What is a CV joint, why do they break and how do you know when you’ve broken one? Here’s everything you need to know about CV joints.

A Constant Velocity Joint, or CV joint, is essentially a driveshaft running from the front differential to each wheel. In an IFS 4WD, the wheels turn and go up and down. That means the CV joint needs to be able to handle up and down movement. And side to side. In a solid-axle application, the CV joint only needs to be able to move side to side. So, while they all look different, they all have the same job, providing drive to your front wheels.

Why do CV joints break?

The ‘joint’ in a CV joint is made of a few components. An outer cage. A series of large ball bearings. An inner race to hold the other side of the bearings, and an axle shaft attached to either end. The main action that kills a CV is shock loading. Like when a spinning wheel lifts off the ground and then lands hard; something that can happen fairly often with an independent suspension system because of the usually limited amount of travel. Shock loading puts massive amounts of pressure on the driveline, and CV joints are usually the weakest link.

This will cause the CV joint cage to physically crack; or in some cases the actual shaft will shear, but this isn’t as common. If you see a 4X4 start to bounce, or hop whilst climbing an obstacle, this is exactly the sort of condition that’ll bust a CV joint. It’s the biggest killer of CVs, but hardly the only contributing factor. Age will fatigue them too. Hundreds of thousands of kilometres of the ball bearings rubbing against the case can fatigue the surrounding material. Especially if you’ve split a protective boot and flung all the precious grease all through your wheel arch.

How you build them counts

Lifting your 4X4 can also cause them to prematurely fail as well. The higher the 4X4, the bigger angle the CV joints need to operate on and the more likely they are to exceed their safe working angles. Think of it a little like getting a flat tyre on your camper in your driveway. Now compare that to getting a flat tyre in the middle of nowhere, an hour from camp as the sun is setting. You can probably handle one, but the other might cause you to break. See what we did there? A diff drop is a common fix here. By lowering the front diff you’re lowering that working angle.

Larger tyres are also a CV joint killer. With the larger rolling diameter and heavier unsprung mass physically putting more pressure on them. Not to mention the increased grip provided by larger off-road orientated tyres. When a tyre lifts and lands hard, the shock loading effect is magnified.

How will I know the CV joint is broken?

If you can hear a clicking noise while making tight turns or accelerating when in 4WD, this is a sure sign your CV joints are on the way out. This applies to both solid-axle vehicles and those with IFS. You’ll potentially hear a loud crack when they snap. Picture the sound of a branch snapping out of a tree and you’re on the money. Finally, unless you’ve got a front locker engaged you’ll suddenly find yourself not going anywhere. The open front diff having an easier time spinning the busted CV that goes nowhere instead of the tyre still planted on ground.

Should you buy genuine or aftermarket?

In most cases, the genuine CV offered from a manufacturer will be the strongest available. Naturally, there are aftermarket companies such as Longfield in the States that make competition-spec chromoly CV joints; but sadly this technology is few and far between in Australia.

Price shopping for a typical dual cab ute we found an extraordinary price difference. OEM offerings from the manufacturer were up around $500 per side. The cheapest we could find online? 1/10th of the price at just $50. Would you trust the cheap offering if you were heading off to the Simmo? Probably not. But there is still a middle ground with reputable parts companies often coming in middle of the price range, but with quality to back it up. Do your research on your specific model. Warranty is a good indicator of quality. As is customer service back-up. Will that fly-by-night parts co help you if you have a claim?

How to look after CV joints

The trick to getting long life from your CV joints, is to not drive aggressively. Mechanical sympathy is key to long lasting and trouble-free motoring. Below are our five top tips to avoid a busted CV Joint:

1. Don’t go nuts tyre wise, stick to the largest legal size for your state;
2. Avoid extreme angles from massive lifts in IFS vehicles;
3. Take care when reversing and avoid using full steering lock under power. This is when a CV is at its weakest;
4. If you are spinning tyres for more than two seconds and aren’t moving forward… stop spinning your tyres; and
5. Avoid shock loading when a tyre lifts. If your 4×4 is bucking like a bull, stop and reassess the obstacle.