Anti-Roll Bar Issues and MOT Failures

The MOT test is a crucial annual inspection designed to ensure your vehicle is safe and environmentally sound. While many drivers are aware of common failure points like worn brakes or bald tyres, some less obvious components can also lead to an MOT failure. One such component is the anti-roll bar, also known as the anti-sway bar or stabilizer bar. This seemingly simple piece of metal plays a significant role in your vehicle's handling and stability, and any damage or wear can indeed result in a failed MOT. This article delves into how anti-roll bar damage can impact your MOT and what you should be looking for.

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 during cornering. When you take a corner, the centrifugal force pushes the vehicle's body outwards, causing it to lean or 'roll'. The anti-roll bar works by resisting this roll, transferring some of the force from the heavily loaded outer wheel to the less loaded inner wheel. This helps to keep the vehicle's body more level, improving stability, handling, and passenger comfort.

Common Anti-Roll Bar Problems

Like any component exposed to the rigours of the road, anti-roll bars and their associated parts can wear out or become damaged over time. The most common issues include:

• Worn or Broken Anti-Roll Bar Links: These are small rods that connect the anti-roll bar to the suspension arms. They often feature ball joints or bushes at each end, which are susceptible to wear and tear.
• Damaged or Corroded Anti-Roll Bar: The bar itself can suffer damage from impacts, such as hitting potholes or road debris. Corrosion can also weaken the metal over time.
• Loose or Damaged Mounting Brackets: The brackets that secure the anti-roll bar to the vehicle's chassis can become loose, corroded, or even break.
• Worn Anti-Roll Bar Bushes: These rubber or polyurethane bushes sit between the anti-roll bar and its mounting brackets. They absorb vibrations and allow the bar to pivot. Over time, these bushes can degrade, crack, or become loose.

How Anti-Roll Bar Damage Affects MOT Tests

The MOT test has specific criteria for suspension components to ensure vehicle safety. The relevant section of the MOT inspection manual focuses on suspension and steering. For the anti-roll bar, the key failure points are:

• Excessive play in anti-roll bar drop links: If the ball joints or bushes in the drop links are worn, there will be noticeable movement. An inspector will check for this by trying to move the link by hand. If there is significant play, it's a failure.
• Cracked or deteriorated bushes: The bushes that hold the anti-roll bar to the chassis are critical. If they are cracked, perished, or missing, the bar can move excessively, affecting stability.
• Damage or corrosion to the anti-roll bar itself: A bar that is bent, cracked, or excessively corroded is considered a structural weakness and a safety hazard. This will result in an MOT failure.
• Loose mountings: If the brackets holding the anti-roll bar are loose or broken, the bar will not function correctly and could detach, posing a significant risk.

Symptoms of a Failing Anti-Roll Bar

Recognising the symptoms of a worn or damaged anti-roll bar can help you address potential issues before they lead to an MOT failure. Keep an ear out for:

• Clunking or rattling noises: These are often heard when driving over bumps or uneven surfaces, especially at lower speeds. This typically indicates worn drop links or bushes.
• Poor handling and increased body roll: If you notice your car leaning excessively in corners, or if the steering feels less responsive, your anti-roll bar system might be compromised.
• Uneven tyre wear: A malfunctioning anti-roll bar can contribute to uneven tyre wear, particularly on the outer edges of the tyres.
• Vehicle pulling to one side: While often associated with steering or wheel alignment issues, a severely damaged anti-roll bar can also cause the vehicle to pull.

MOT Inspection Process for Anti-Roll Bars

During the MOT test, the inspector will systematically check the suspension system. For the anti-roll bar, this involves:

1. Visual Inspection: The inspector will look for obvious signs of damage, corrosion, or missing components on the anti-roll bar, its links, bushes, and mounting brackets.
2. Physical Checks: They will attempt to move the anti-roll bar and its drop links by hand to detect any play or looseness in the joints and bushes.
3. Leverage Tests: Sometimes, a pry bar might be used to gently test the integrity of the bushes and mountings.

Any findings that are deemed to pose a risk to the safety of the driver or other road users will result in a failure.

Can You Drive with a Broken Anti-Roll Bar?

While your vehicle might still be drivable with a damaged or broken anti-roll bar, it is strongly advised not to. The primary function of the anti-roll bar is to maintain stability, especially during cornering and emergency manoeuvres. Driving without a properly functioning anti-roll bar significantly compromises your vehicle's handling, making it more prone to skidding or rolling over, particularly at higher speeds or during sharp turns. It also puts undue stress on other suspension components. For your safety and the safety of others, it's best to have the vehicle repaired immediately.

Repairing Anti-Roll Bar Issues

Replacing worn or damaged anti-roll bar links, bushes, or the bar itself is a relatively common repair. The cost can vary depending on the vehicle model and the specific parts that need replacing. Typically, replacing drop links and bushes is more straightforward and less expensive than replacing the entire anti-roll bar. It's often recommended to replace components on both sides of the vehicle simultaneously to ensure balanced suspension performance. For example, if one drop link is worn, it's highly likely the other one is not far behind.

Table: Common Anti-Roll Bar Failures vs. Symptoms

Frequently Asked Questions (FAQs)

Q1: How much does it typically cost to fix an anti-roll bar?

The cost can vary significantly. Replacing just the drop links and bushes might cost between £100 and £300, depending on your vehicle and garage. Replacing the entire anti-roll bar could be more, potentially £200-£500 or more, as it's a more involved job.

Q2: Can I replace anti-roll bar components myself?

If you have a good understanding of car mechanics and the right tools, you might be able to replace anti-roll bar links or bushes. However, suspension work can be dangerous if not done correctly, and it's often best left to qualified professionals to ensure the job is done safely and effectively.

Q3: Should I replace both anti-roll bar links at the same time?

Yes, it is highly recommended. Suspension components wear out symmetrically. If one link is worn, the other is likely to be close to failure. Replacing both ensures balanced suspension performance and prevents you from having to do the job again soon.

Q4: What's the difference between an anti-roll bar and a shock absorber?

While both are crucial suspension components, they serve different purposes. Shock absorbers (or dampers) control the up-and-down movement of the wheels, absorbing road shocks and keeping the tyres in contact with the road. The anti-roll bar, as discussed, primarily controls lateral (sideways) body roll during cornering, improving stability.

Conclusion

In summary, damage or significant wear to your vehicle's anti-roll bar, its links, bushes, or mounting brackets can absolutely lead to an MOT failure. These components are vital for maintaining your vehicle's stability and safe handling. Regular checks and addressing any unusual noises or handling characteristics promptly can save you from an unexpected MOT failure and, more importantly, ensure your vehicle remains safe to drive. If you suspect an issue with your anti-roll bar system, it's always best to consult a qualified mechanic.