CV Joint Failure and Your MOT Test

The Crucial Role of CV Joints in Your Vehicle

The MOT test is a vital annual inspection designed to ensure your vehicle is safe and roadworthy. While many drivers focus on brakes, tyres, and lights, components like the Constant Velocity (CV) joints, though often unseen, play a significant role in your car's ability to operate safely. A failing CV joint can have serious consequences, not just for your vehicle's performance but also for your MOT result. This article delves into what happens if a CV joint fails a MOT test, exploring the common causes of failure, the signs to look out for, and why it's imperative to address them promptly.

Understanding CV Joints

Before we discuss MOT failures, it's essential to grasp what CV joints are and what they do. CV joints, also known as U-joints in some contexts, are flexible couplings that connect the driveshaft to the wheels. Their primary function is to transmit power from the gearbox to the wheels while allowing for the suspension's movement and steering angles. This means they must be able to operate smoothly and reliably whether the wheels are turning straight ahead, angled for a corner, or moving up and down with the suspension. They are typically found on front-wheel-drive vehicles and some rear-wheel-drive vehicles with independent rear suspension.

Common Causes of CV Joint Failure

CV joints are robust components, but like any part of a car, they can wear out over time or suffer damage. The most common culprit behind CV joint failure is a damaged or torn CV boot. The CV boot is a rubber or silicone covering that protects the joint from dirt, water, and debris. It's also crucial for retaining the lubricating grease that keeps the joint functioning smoothly. When the boot tears, the protective grease escapes, and abrasive contaminants enter the joint. This ingress of dirt and grit accelerates wear and tear significantly, leading to the characteristic clicking or grinding noises associated with a failing CV joint.

Other causes of failure can include:

• Excessive stress: Aggressive driving, such as rapid acceleration or frequent hard cornering, can place undue stress on CV joints, leading to premature wear.
• Manufacturing defects: Although less common, a faulty CV joint from the factory can fail sooner than expected.
• Impact damage: Hitting potholes or road debris can directly damage the CV joint or the protective boot.

Signs of a Failing CV Joint

Recognising the early signs of CV joint failure is crucial for preventing more significant damage and avoiding an MOT failure. The most tell-tale symptom is a clicking or popping noise that becomes more pronounced when turning. This noise typically emanates from the wheel area and is often described as a rhythmic clicking that speeds up as the vehicle accelerates. You might also notice:

• Vibrations: As the joint deteriorates, you might feel vibrations through the steering wheel or the floor of the car, especially during acceleration.
• Grease leaks: If you inspect the area around your CV joints, you might see black, greasy residue on the inside of the wheel or suspension components. This is a strong indicator that a CV boot has failed.
• Uneven tyre wear: In some cases, a severely damaged CV joint can contribute to uneven tyre wear.

CV Joints and the MOT Test

The MOT test specifically checks for safety-critical components. According to MOT testing guidelines, a CV joint will result in a fail if:

• There is evidence of cracking, splitting, or perishing of the gaiter (CV boot). Even if the joint itself appears to be functioning correctly, a damaged gaiter is considered a failure as it will inevitably lead to joint deterioration.
• The driveshaft joint is excessively worn. This is usually identified by excessive play or roughness when the tester manipulates the driveshaft.
• There is a noticeable and audible noise from the joint when tested. This would indicate significant wear and potential failure.

The MOT tester will inspect the CV boots for any signs of damage. They will also check for excessive play in the driveshafts. If a CV joint is making a distinct noise or if the gaiter is clearly torn or perished, your vehicle will not pass the MOT.

Consequences of a Failed MOT Due to CV Joints

Failing your MOT means your vehicle is not legally permitted to be driven on public roads. You will receive a refusal of an MOT test certificate, and you will need to arrange for the necessary repairs to be carried out. Driving a vehicle that has failed its MOT is illegal and can result in fines and penalty points on your driving licence. Furthermore, a failing CV joint, if left unaddressed, can lead to more severe problems. A completely seized or broken CV joint can cause a sudden loss of drive, potentially leaving you stranded. In severe cases, a failing joint could even detach, causing significant damage to other vehicle components or posing a serious safety risk.

Repairing or Replacing CV Joints

The good news is that CV joints are generally repairable, although often the most cost-effective solution is to replace the entire driveshaft assembly, which includes the CV joint. The process involves:

1. Lifting the vehicle: Safely raising the car on a lift or jack stands.
2. Removing the wheel: To gain access to the CV joint.
3. Disconnecting suspension components: To allow the driveshaft to be removed.
4. Replacing the CV joint or driveshaft: This is the core of the repair. If only the boot is damaged, a skilled mechanic can sometimes replace just the boot and re-grease the joint, but this is often a more labour-intensive and less reliable long-term solution than replacing the entire unit.
5. Reassembly: Putting all the components back together.
6. Wheel alignment: It's often recommended to have a wheel alignment after replacing driveshafts or significant suspension components.

The cost of repair will vary depending on the make and model of your vehicle, whether you opt for genuine or aftermarket parts, and the labour rates of your chosen garage. Replacing a CV boot alone is cheaper, but if the joint has already been contaminated, it's often a false economy. Replacing the entire CV joint or driveshaft is generally more expensive but provides a more durable and reliable fix.

Preventative Maintenance: Protecting Your CV Joints

Preventative maintenance is key to avoiding costly repairs and MOT failures. The most effective way to protect your CV joints is to regularly inspect the CV boots for any signs of damage. Look for cracks, splits, or grease leaks around the rubber gaiters. If you notice any damage, get it repaired as soon as possible. A simple CV boot replacement is significantly cheaper than replacing a damaged CV joint or a full driveshaft. Keeping your vehicle clean, especially the underside, can also help prevent the build-up of abrasive materials that can damage the boots.

Frequently Asked Questions

What does a clicking noise when turning mean?

A clicking or popping noise when turning is the most common symptom of a failing outer CV joint. It indicates that the joint is worn and is not articulating smoothly under the stress of steering.

Can I pass my MOT with a torn CV boot?

No, a torn or perished CV boot is an automatic MOT failure. The integrity of the boot is crucial for protecting the CV joint.

How much does it cost to fix a CV joint?

The cost can vary widely, but expect to pay anywhere from £150 to £500 or more for a CV joint replacement, depending on the vehicle and parts used. Replacing just a CV boot is considerably cheaper, typically in the range of £80 to £200.

How long does a CV joint last?

With proper maintenance and without significant damage, CV joints can last for many years and tens of thousands of miles. However, factors like driving style and the integrity of the CV boots can significantly affect their lifespan.

Should I replace just the boot or the whole CV joint?

If the CV boot is torn but the joint shows no signs of wear (no clicking or roughness), replacing just the boot is an option. However, if there's any doubt, or if the joint has already started to make noise, replacing the entire CV joint or driveshaft is often the more reliable long-term solution.

Conclusion

The MOT test is a critical juncture for ensuring your vehicle's safety. A failed CV joint, often heralded by a torn CV boot, is a common reason for a vehicle to be refused its MOT certificate. Understanding the signs of wear, the causes of failure, and the importance of preventative maintenance can save you money, hassle, and, most importantly, ensure your vehicle remains safe for you and other road users. Regularly check those CV boots, listen for unusual noises, and address any issues promptly to keep your car roadworthy and your MOT certificate in hand.

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