15/11/2004
The annual MOT test is a crucial rite of passage for every vehicle over three years old in the UK, designed to ensure your car meets minimum road safety and environmental standards. While many components can lead to a failure, two issues often catch drivers off guard: a leaking exhaust system and corroded brake pipes. Both pose significant safety risks and are high on an MOT examiner's checklist. Understanding what constitutes a failure in these areas, how to spot potential problems, and what repair options are available can save you a great deal of stress, time, and money.
A car's exhaust system is far more than just a noise reducer; it's integral to managing harmful emissions and maintaining engine performance. From the manifold to the tailpipe, a series of pipes, catalytic converters, and silencers work in harmony. Any breach in this system, no matter how small, can lead to an MOT failure. The primary concerns revolve around noise pollution, the escape of noxious gases into the vehicle's cabin, and the failure to properly process exhaust gases, leading to higher emissions. An exhaust leak can manifest as an unusually loud engine, a distinct smell of exhaust fumes, or even a visible puff of smoke from an unexpected location under the car. Testers will look for any holes, cracks, or loose connections that allow gases to escape prematurely. Even a minor pinhole leak can be enough to warrant a fail, especially if it compromises the emissions readings or creates excessive noise. The integrity of the exhaust system is paramount for both environmental compliance and the safety of vehicle occupants.
Beyond the exhaust, the braking system is arguably the most critical safety feature of any vehicle. Brake pipes, typically made of steel, carry hydraulic fluid under immense pressure from the master cylinder to the brake calipers and drums at each wheel. Over time, these pipes are exposed to the elements – road salt, moisture, and debris – making them highly susceptible to corrosion. This is a particularly insidious problem because it can degrade the pipe's integrity from the outside in, potentially leading to a sudden and catastrophic brake failure. An MOT examiner will meticulously inspect all brake pipes and hoses for signs of damage, especially corrosion.
The question of what constitutes 'excessive corrosion' on brake pipes is a common point of contention and confusion for many motorists. It's not just about surface rust; a certain degree of surface oxidation is normal and acceptable. However, if the corrosion has led to pitting or flaking that has significantly reduced the pipe's wall thickness, or if it has caused a structural weakness, it will result in an immediate MOT failure. The key criterion is whether the pipe's structural integrity has been compromised. Testers are looking for corrosion that is deep enough to be deemed a safety risk, not just cosmetic blemishes. If you can scrape off the rust with your fingernail and see sound metal beneath, it might pass. If the rust is flaking off in layers, or if the pipe feels thin or spongy, it's almost certainly a fail.
When an MOT report states 'brake pipes corroded/pitted nearside front, offside front, nearside rear, offside rear, going into flexi hoses', it typically means the corrosion is located on the rigid metal pipes just before they connect to the flexible rubber hoses that go to the brake calipers/cylinders at each wheel. This is often good news, as it suggests the corrosion is confined to shorter sections of pipe rather than the entire length running under the car. While replacing these shorter sections is still a job for a skilled mechanic, it's generally less extensive and therefore less costly than replacing the entire length of pipe from front to back, which involves much more dismantling and routing. However, it's vital that any replacement sections are properly flared and joined to prevent leaks under pressure.
Spotting Issues Before Your MOT
Proactive checks can save you from an unexpected MOT failure. Here's what to look for:
- Exhaust Leaks:
- Listen for a louder than usual exhaust note, a blowing sound, or a ticking noise, especially when cold.
- Look for black sooty marks around pipe joints or on the exhaust itself, indicating gas escape.
- Run your hand (carefully, when cold) around joints and pipes to feel for escaping air.
- Consider a 'rag test': briefly block the tailpipe with a rag (wear gloves) while the engine idles. If the engine stalls quickly, your exhaust is likely sealed. If it continues to run, there's a leak somewhere.
- Brake Pipe Corrosion:
- Jack up your car safely (or use a ramp if available) to get a good look underneath.
- Follow the brake pipes from the master cylinder (under the bonnet) along the chassis to each wheel.
- Pay close attention to areas where pipes run close to wheels, fuel tanks, or where they might collect water and road debris.
- Use a wire brush to gently clean off any surface rust to reveal the true condition of the pipe. If you find deep pitting, flaking, or a significant reduction in pipe thickness, it's a concern.
- Check the flexible hoses too for cracks, bulges, or perishing.
What to Do If Your Car Fails
If your car fails its MOT due to an exhaust leak or corroded brake pipes, don't despair. You have a few options:
- Understand the Report: The MOT failure document will detail the specific reasons for the fail. Make sure you understand exactly what needs repairing.
- Get Quotes: Shop around for repair quotes. While your MOT garage can often do the repairs, you're not obliged to use them. Get at least two or three quotes to compare.
- Repair and Re-test: Once the repairs are completed, your car will need a re-test. If you have the repairs done at the same MOT centre within 10 working days, a partial re-test is often free or at a reduced cost. If you take it elsewhere or exceed the time limit, a full re-test fee will usually apply.
Cost Implications of Repairs
The cost of repairs for exhaust leaks and corroded brake pipes can vary significantly based on the specific vehicle, the extent of the damage, and the garage you choose. Here are some ballpark figures:
| Repair Type | Estimated Cost (GBP) | Notes |
|---|---|---|
| Minor Exhaust Leak (e.g., small hole, loose joint) | £50 - £150 | Might involve welding or replacing a small section. |
| Major Exhaust Repair (e.g., catalytic converter, full section) | £200 - £600+ | More complex, parts are expensive. |
| Corroded Brake Pipe (short section at wheel) | £80 - £200 per wheel | Includes parts (pipe, fluid), labour, and bleeding the system. |
| Corroded Brake Pipe (full length replacement) | £300 - £700+ | Significantly more labour-intensive, may require removing fuel tank or suspension components. |
| Corroded Brake Flexi Hoses | £50 - £150 per hose | Less common for corrosion, but they can perish. |
It's important to note that these are general estimates. Always obtain a detailed quote from a reputable garage before proceeding with any work. For brake pipe replacement, the system will also need to be bled to remove air, a critical step for proper brake function.
Frequently Asked Questions (FAQs)
Q: Can a small exhaust leak really fail the MOT?
A: Yes, absolutely. Even a small leak can cause an MOT failure, especially if it leads to excessive noise, affects the vehicle's emissions readings, or allows exhaust fumes to enter the passenger compartment. The MOT test is very strict on exhaust integrity.
Q: How much corrosion on brake pipes is 'excessive' for an MOT fail?
A: 'Excessive' corrosion means that the pipe's structural integrity has been compromised. Surface rust that can be wiped off is usually acceptable. However, if the corrosion has caused pitting, flaking, or a noticeable reduction in the pipe's wall thickness, it will fail. Testers often use a blunt tool to gently test the strength of the corroded area.
Q: Is it expensive to replace corroded brake pipes?
A: It can be. The cost varies significantly depending on how much pipe needs replacing. Short sections near the wheels are cheaper, often £80-£200 per corner. Replacing a full length of pipe from front to back can be much more expensive, potentially £300-£700+, due to the increased labour involved in routing new lines and bleeding the entire system.
Q: Can I repair a corroded brake pipe myself?
A: Replacing brake pipes requires specialist tools (like a flaring kit) and knowledge to ensure a leak-free and safe repair. More importantly, after any work on the brake system, it must be properly bled to remove air, which can cause total brake failure if not done correctly. Due to the critical safety aspect, this job is best left to experienced mechanics.
Q: What's the difference between a brake pipe and a flexi hose?
A: Brake pipes are the rigid, usually steel, lines that run along the car's chassis, carrying brake fluid. Flexi hoses (or flexible hoses) are shorter, reinforced rubber lines that connect the rigid pipes to the brake calipers or wheel cylinders. They allow for the movement of the suspension and steering without breaking the brake fluid connection. Both are critical for brake function and are inspected during an MOT.
Understanding these common MOT failure points can significantly improve your chances of passing. Regular inspections and addressing minor issues before they escalate are key to maintaining your vehicle's roadworthiness and ensuring your own safety, as well as that of other road users.
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