Anti-Roll Bars: MOT Failures & Maintenance

The MOT test is a crucial annual check designed to ensure your vehicle is safe and roadworthy. While many drivers focus on the obvious components like brakes and tyres, less visible parts can also lead to a failed MOT. One such component is the anti-roll bar, also known as the sway bar. This seemingly simple piece of metal plays a vital role in your car's handling and stability, and if it's not in good condition, it can indeed result in a failed MOT. This article will delve into how an anti-roll bar can fail an MOT, what signs to look out for, and how to maintain it to avoid unexpected failures.

What is an Anti-Roll Bar?

Before we discuss MOT failures, it's essential to understand what an anti-roll bar is and what it does. The anti-roll bar is a U-shaped metal bar that connects the left and right sides of your vehicle's suspension. Its primary function is to reduce body roll when cornering. Without it, your car would lean significantly in turns, making it unstable and less predictable. The bar works by transferring some of the force from the heavily loaded wheel on the outside of a turn to the less loaded wheel on the inside, effectively counteracting the lean. This improved stability enhances both safety and driving comfort.

How Can an Anti-Roll Bar Fail an MOT?

The MOT test checks for specific defects that could compromise your vehicle's safety. When it comes to the anti-roll bar, the primary reasons for failure revolve around its condition and the security of its mountings. Here are the key areas the MOT inspector will scrutinise:

1. Corrosion and Damage

Like many metal components exposed to the elements, anti-roll bars are susceptible to corrosion. Rust can weaken the bar, making it more prone to breaking. The MOT test will fail a vehicle if the anti-roll bar is:

• Severely corroded: Significant rust compromising the structural integrity of the bar.
• Cracked or broken: Any visible cracks or breaks in the bar itself are a definite fail.
• Damaged: Bent or distorted anti-roll bars can affect handling and are considered a safety defect.

A severely corroded or broken anti-roll bar can snap during driving, leading to a sudden loss of control, especially during cornering. This is why it's a critical safety item for the MOT.

2. Worn or Damaged Drop Links

The anti-roll bar is connected to the suspension arms via drop links (also known as anti-roll bar links or stabiliser links). These links often have ball joints or bushings that can wear out over time. The MOT test checks for:

• Excessive play in drop link joints: Worn ball joints will have too much movement, leading to knocking noises and poor handling.
• Damaged or perished bushings: Rubber bushings can degrade, crack, or become loose, allowing for excessive movement.
• Corroded or damaged drop links: Similar to the bar itself, the links can also corrode and become weak or broken.

If the drop links are too worn, they won't effectively connect the anti-roll bar to the suspension, negating its stabilising effect and potentially causing the bar to detach. This is a common reason for an MOT failure related to the anti-roll bar system.

3. Loose or Damaged Mountings

The anti-roll bar is secured to the vehicle's chassis or subframe by rubber mounting brackets. These brackets hold the bar in place and absorb some vibration. The MOT inspector will check:

• Loose mountings: If the brackets are not securely fastened, the bar can move excessively.
• Damaged or perished mounting rubbers: The rubber components can degrade, crack, or be missing entirely, allowing the bar to move and rattle.
• Corrosion around mounting points: Severe corrosion on the chassis where the mounts attach can also lead to a fail, as it compromises the security of the entire assembly.

A loose anti-roll bar can create significant noise, affect handling, and in severe cases, detach from the vehicle, posing a serious safety risk. Secure mountings are paramount.

Signs of a Failing Anti-Roll Bar System

While you should always rely on an MOT inspection for a definitive assessment, there are several common signs that your anti-roll bar system might be developing a problem:

• Knocking or Clunking Noises: This is perhaps the most common symptom, often heard when going over bumps, uneven surfaces, or during cornering. It typically indicates worn drop links or loose anti-roll bar mountings.
• Poor Handling and Increased Body Roll: If you notice your car leaning more than usual in corners, or if the steering feels less responsive, it could be a sign that the anti-roll bar is not functioning correctly, likely due to wear or damage.
• Rattling Sounds: A loose anti-roll bar can sometimes rattle against its mounts, especially at lower speeds or when the suspension is working.
• Uneven Tyre Wear: While less direct, a compromised anti-roll bar can contribute to uneven weight distribution during cornering, which might manifest as accelerated or uneven tyre wear over time.

Maintaining Your Anti-Roll Bar System

Regular maintenance and vigilance are key to preventing an MOT failure related to your anti-roll bar. Here's what you can do:

1. Visual Inspections

Whenever you have your car on a ramp for other maintenance, take a moment to visually inspect the anti-roll bar and its drop links. Look for:

• Signs of rust or corrosion on the bar and links.
• Any visible cracks, bends, or damage.
• The condition of the rubber bushings – check for cracks, perishing, or excessive wear.
• The security of the mounting brackets.

2. Listen for Noises

Pay attention to any new noises coming from your suspension. Knocking, clunking, or rattling sounds, especially when turning or going over bumps, should not be ignored and warrant a closer inspection.

3. Professional Servicing

Ensure your vehicle receives regular professional servicing. A qualified mechanic will check the condition of your suspension components, including the anti-roll bar and drop links, as part of a routine service. This proactive approach can identify potential issues before they become serious or lead to an MOT failure.

Anti-Roll Bar Components and Their MOT Relevance

Let's break down the key components of the anti-roll bar system and their MOT implications:

Frequently Asked Questions (FAQs)

Q1: Can a slightly rusty anti-roll bar fail an MOT?

A1: Yes, if the rust is considered 'severe' and compromises the structural integrity of the bar, it can fail. Minor surface rust might be acceptable, but any significant pitting or flaking could be an issue.

Q2: How much does it cost to replace anti-roll bar drop links?

A2: The cost can vary depending on the vehicle make and model, and whether you use genuine or aftermarket parts. Typically, replacing a pair of drop links can range from £80 to £250, including parts and labour, but it's always best to get a specific quote from your mechanic.

Q3: Can I drive with a broken anti-roll bar?

A3: It is not recommended. While your car might still be drivable, its handling and stability will be significantly compromised. This increases the risk of losing control, especially during cornering or on uneven surfaces, making it unsafe to drive.

Q4: How often should anti-roll bar drop links be checked?

A4: It's a good idea to have them checked during your car's annual service. If you hear knocking noises or notice changes in handling, you should get them inspected immediately, regardless of the service schedule.

Conclusion

The anti-roll bar and its associated components are critical for your vehicle's handling and safety. While often overlooked by drivers, they are thoroughly checked during the MOT test. Understanding the potential failure points – corrosion, damage to the bar and links, and loose mountings – can help you proactively maintain your vehicle. Regular visual checks, listening for unusual noises, and adhering to a professional servicing schedule are the best ways to ensure your anti-roll bar system remains in good condition, preventing unexpected MOT failures and, more importantly, keeping you and other road users safe. Don't underestimate the importance of this vital suspension component; a well-maintained anti-roll bar contributes significantly to a secure and enjoyable driving experience.