CV joint: what it does, symptoms of a bad one and when to replace it

A CV joint (constant velocity joint) is the joint at each end of your drive shaft that keeps power flowing to the wheel while it steers and moves up and down. A clicking or ticking noise when you turn at low speed is almost always a worn outer CV joint. Replace it soon: a worn joint can fail completely.

When that happens you lose drive to that wheel, often at the worst moment, on a roundabout or halfway across a junction. And long before that, a split CV boot is enough to fail the MOT in the UK or the APK in the Netherlands. Below you will read how a CV joint works, how to tell a bad one from other drivetrain noises, and how to choose the smallest repair that actually solves the problem.

What is a CV joint and what does it do?

A CV joint sits at both ends of the drive shaft. The shaft itself is a solid or hollow steel bar that carries torque from the gearbox to the wheel. The joints at its ends do the real work: they let the shaft keep transmitting power while the angle between gearbox and wheel changes all the time.

On a front-wheel-drive car two things happen to the same wheel at once. It steers left and right, and it moves up and down over speed bumps and potholes. The drive shaft has to keep turning at a changing angle and change length at the same time. Driven rear axles and four-wheel-drive cars with independent suspension use CV joints too, usually at smaller angles.

Why not an ordinary universal joint?

An ordinary universal joint (a Cardan or Hooke’s joint) can also turn at an angle, but not evenly. At an angle, the output shaft speeds up and slows down twice per revolution even when the input shaft turns at a steady speed. You feel that as a pulsing vibration, which is exactly what you do not want on a steered front wheel.

Hence the name: constant velocity means the output side turns at the same speed as the input side. In a ball-type CV joint the balls sit in the plane that splits the angle between the two shafts exactly in half, so the output shaft keeps pace with the input shaft, even at full steering lock. The result is smooth drive at angles where a universal joint would shake.

Outer and inner CV joint: what is the difference?

Every drive shaft has two CV joints, and they are built differently because they do different jobs.

The outer CV joint (ball type)

At the wheel end sits a ball-type joint, usually a Rzeppa design or a development of it: a cage with six balls that run in grooves between an inner and an outer race. It handles large angles (typical Rzeppa joints allow around 45 to 48 degrees) but it cannot slide in and out. It is the joint that works hardest, because it follows the full steering lock in every turn.

The inner CV joint (tripod)

At the gearbox end there is usually a tripod joint: a three-pointed yoke with rollers that run in a housing with three grooves. It works at smaller angles but it can slide lengthways (plunge). That matters, because when the suspension moves, the distance between gearbox and wheel changes. Without that sliding room the shaft would bind and put heavy loads on the bearings in the gearbox and the hub.

The CV boot is usually where it starts

A CV joint rarely wears out on its own. In practice the damage almost always starts at the rubber CV boot (also called a CV gaiter), the bellows-shaped cover that keeps the special grease in and the dirt out.

The chain of events usually goes like this:

1. The boot hardens and splits, through age, frost, road salt or contact with a kerb.
2. The rotation flings the grease out. You see it as spatters on the inside of the wheel and on the undertray.
3. Water, grit and road dirt get in on every wet drive.
4. The joint keeps running dry and dirty. The tracks wear, play develops, and the noise starts.

That is why it pays to look under the car at every service. A split boot spotted early is a small job. The same split left for months means a new CV joint or a complete drive shaft.

Symptoms of a bad CV joint

The signs are fairly specific, which makes a CV joint easier to recognise than many other drivetrain complaints.

Clicking or ticking when you turn

This is the classic symptom of a worn outer CV joint. You turn at low speed with a lot of steering lock, for example when parking or on a roundabout, and hear a rhythmic click-click-click that speeds up with the wheels. Accelerate in the turn and it gets louder. Drive straight on and it disappears.

Do not rely on which side you think it comes from. Some guides say a noise in a left turn means the left joint, others say the opposite, and in our experience the sound carries. We test both sides on the road and check each joint for play on the lift before any part is ordered.

Vibration or a clunk when you pull away

A worn inner CV joint behaves differently. It gives a vibration or a clunk when you pull away, especially under load and sometimes only at a certain speed. If the car mainly feels as if it jerks when you pull away, rule out other causes too: see why your car jerks or stutters. If the revs rise without the car speeding up, that points to a slipping clutch rather than a CV joint.

Grease on the inside of the wheel

Look at the inside of the wheel rim and under the car. Dark, greasy spatters in a fan pattern around the shaft prove that a boot is leaking. Often you can see the split itself, or a clamp that has come loose.

When it is not the CV joint

Not every drivetrain noise is a CV joint. A humming or whining noise that rises with speed and changes as soon as you turn points more towards a wheel bearing or the differential. A clunk when you change gear, a gear that is hard to select or a noise that changes with each gear belongs to the gearbox, not the CV joint: see gearbox failure symptoms. And an automatic gearbox that does not shift properly can feel similar from the driver’s seat but has a completely different cause.

This is where a drivetrain specialist earns their keep. We look at the whole chain, from gearbox to wheel, so you replace the part that is actually worn and not the one that happened to be easiest to reach.

Is it safe to drive with a bad CV joint?

No, not for long. While it only clicks the car can still be driven, but you are only postponing the problem. As the play increases, the joint can fail completely. You then lose drive to that wheel, which is unpleasant if it happens in the middle of a junction.

In the worst case the joint breaks apart and the drive shaft comes loose. A loose shaft that is still turning can damage a brake line, the wheel arch or parts of the suspension. So do not drive around for months on a clicking CV joint.

A split CV boot fails the MOT and the APK

Safety aside, a split boot is also an inspection point. In the UK MOT inspection manual, a constant velocity joint boot that is “missing, split or insecure so that it no longer prevents the ingress of dirt” is a major defect, which means a fail. A severely deteriorated boot is a minor defect. In the Netherlands, the APK also checks the drive shafts, and in our experience a boot that leaks grease or lets dirt in leads to a rejection. Either way, you will have to repair it. Have the boots checked before the inspection, so you do not end up repairing under time pressure with a rejected car.

CV joint replacement: three options

What needs doing depends on how early you catch it.

1. Replace only the CV boot. Possible when the split is fresh and the joint has no play yet. The shaft comes out, the joint is cleaned, regreased and fitted with a new boot and clamps. This is the smallest repair, but it only makes sense if no dirt has got in yet.
2. Replace the CV joint. If there is already play or the tracks are worn, the joint is replaced completely, with a new boot and grease.
3. Replace the complete drive shaft. Often the practical choice: you get both joints and both boots new in one go, and in labour that can work out better than replacing separate parts. When that is the sensible route is explained in our article on the drive shaft.

The job means undoing the hub nut and usually part of the suspension. At the gearbox end, gearbox oil can escape when the inner joint comes out, so the oil seal has to be checked and the gearbox oil topped up to the correct level afterwards. It is work best left to someone who works on drivetrains every day.

What affects the cost of CV joint replacement?

There is no fixed price, because cars differ a lot. What you end up paying depends mainly on:

• Which repair is needed. A boot alone is a different order of magnitude from a complete drive shaft.
• Inner or outer. The inner joint sits deeper and often needs more dismantling.
• The car. On one car the shaft is out in no time, on another a lot of suspension and undertray has to come off. Seized hub nuts and hub carriers take extra time.
• Drive and design. Four-wheel drive, an intermediate shaft bearing or a shaft with a vibration damper makes the job more involved.
• Choice of parts. Original, a good aftermarket brand or remanufactured makes a difference in price and in lifespan.
• Further damage. If the joint has run dry for a long time, the gearbox oil seal or the wheel bearing may be damaged too.

Contact us for a price indication based on your registration number and complaint. With the registration and a short description of the noise, we can usually tell you what to expect.

Frequently asked questions about CV joints

What exactly is a CV joint?

A CV joint is a joint in the drive shaft that transmits power at a changing angle without the rotational speed fluctuating. That is where the name comes from: constant velocity, the same speed on the input and output side. A front-wheel-drive car has one at each end of both drive shafts.

What does a bad CV joint sound like?

A rhythmic clicking or ticking, heard mostly at low speed with a lot of steering lock, that gets louder when you accelerate in the turn. Driving straight on you usually hear nothing. A vibration or clunk when pulling away points more towards the inner CV joint.

Which side is the bad CV joint on?

You cannot reliably tell from the driver’s seat. Guides disagree on whether a noise in a left turn means the left or the right joint, and the sound carries through the car. A workshop checks both joints for play on a lift and looks at both boots before ordering parts.

Can I replace just the CV boot?

Yes, if you catch it early. If there is still enough grease in the joint and it has no play or noise, a new boot with fresh grease is enough. If it already clicks, the damage inside is usually done and the joint needs replacing.

Can I replace a CV boot myself?

You can if you are used to working on suspension, but it is more than a rubber job. The hub nut has to come undone and the shaft usually comes out. The old grease and any dirt must be cleaned out of the joint, and the new boot needs fresh grease and properly tightened clamps. If you remove the inner joint, check the gearbox oil level afterwards. If the joint already clicks, a new boot will not cure it.

How long can I drive with a clicking CV joint?

There is no reliable time limit; it depends on how much play there already is and how you drive. Do not assume it will last another season. Have it checked soon, certainly before a long journey or a trip abroad.

Will a split CV boot fail the MOT or APK?

Yes. In the UK a boot that is missing, split or insecure so that it no longer keeps dirt out is a major defect, so the car fails. In the Netherlands, in our experience, a boot that leaks grease or lets dirt in leads to an APK rejection, even if the car otherwise drives normally.

Is a CV joint the same as a drive shaft?

No. The drive shaft is the shaft that carries power from the gearbox to the wheel; the CV joints are the joints at its two ends. You can often replace one joint or one boot on its own, or the complete shaft with both joints when that is more practical.

Can a bad CV joint damage the gearbox?

Rarely directly, but there is a link. A worn or binding inner joint can put extra load on the bearings and the oil seal at the gearbox output, and when the inner joint is removed gearbox oil can escape. That is why we always check the seal and the gearbox oil level when we replace an inner CV joint or a drive shaft.

Have your CV joint checked

Do you hear clicking when you turn, feel a vibration when you pull away or see grease on the inside of your wheel? Have it checked before the joint gives up. We are specialists in gearboxes and drivetrains and look not only at the CV joint but at the rest of the drivetrain as well, from gearbox to wheel. Our workshop is in Montfoort, in the province of Utrecht; if you are in the area, see also our drivetrain and gearbox work in and around Utrecht.

Book your car in, or first find out what your symptom could mean.

For garages: not sure whether a vibration comes from a CV joint or from the gearbox? With ATR Remote we read the transmission remotely, so you can rule the gearbox in or out before you replace parts.