Brake pipe corroded MOT advisory: what it means and what to do
A corroded brake pipe advisory means the tester saw rust on the outside of one of the thin metal pipes that carry brake fluid to the wheels, but not enough to fail it. Take it seriously. Brake pipes are under high pressure every time you press the pedal, and a pipe that rusts through can split during hard braking. Get the pipes looked at soon, and before winter if you can.
Why brake pipes rust
Most cars leave the factory with steel brake pipes that have a protective coating. Over the years road salt, water and stone chips wear through it, and the steel underneath starts to rust. The worst spots are where pipes run along the underside near the fuel tank and rear axle, under clips, and anywhere mud collects.
Light surface rust is very common on older cars and isn't a problem by itself. The concern is rust that's eating into the pipe wall.
When it becomes an MOT fail
The MOT inspection manual is specific about brake pipes:
| What the tester finds | Category |
|---|---|
| Pipe not properly clipped or supported | Minor |
| Pipe damaged or excessively corroded | Major (fail) |
| Pipe likely to become detached or damaged | Major (fail) |
| Pipe at imminent risk of failure or fracture | Dangerous |
| Leaking pipe or connection on a hydraulic system | Dangerous |
The manual's guidance is that a pipe should fail when its wall thickness looks reduced by about a third, which is roughly 0.25mm on a typical car pipe. That's not much metal. It also tells testers to give the benefit of the doubt when they're not sure, which is why an advisory can sometimes be closer to a fail than it sounds.
"Covered in grease or other material"
The full wording on a lot of MOTs is "Brake pipe corroded, covered in grease or other material". The second half means the tester couldn't see the pipe properly. It may be coated in underseal, wax, oil or road muck.
That's worth knowing, because it means nobody has seen what the metal under the coating looks like. A garage can clean a section and check it. Sometimes it's fine. Sometimes the coating is hiding worse rust than the tester could see.
What a replacement costs
The price depends on how many pipes need doing and how hard they are to reach.
| Job | Rough price at an independent garage |
|---|---|
| One short section, easy to reach | £80 to £150 |
| Several pipes or a run along the floor | £150 to £350 |
| Full set, where the fuel tank or subframe has to come down | £350 to £600 or more |
The fluid has to be topped up and the system bled afterwards, which is included in a normal quote.
Many garages replace steel pipes with copper-nickel pipe (often sold as Kunifer). It's easier to bend and it doesn't rust in the same way, so you're unlikely to see this advisory again. Plain copper pipe isn't the same thing and isn't suitable.
Can you do it yourself?
Making up and flaring brake pipes needs the right flaring tool, and the old unions are often seized solid into the next part. Then the system has to be bled properly. It's a job for people who've done brakes before. If a pipe is badly rusted, a garage with a lift is the safer bet.
Brake hoses are a different advisory
Flexible brake hoses are the rubber sections that link the metal pipes to each wheel, so the wheel can move. They get advisories for being "deteriorated", "slightly damaged" or "chafed". A hose that's only slightly damaged is a minor defect, and an excessively damaged, bulging or leaking one fails. Replacing a hose usually costs £60 to £150 each.
What to do now
Get a garage to look at the pipe on a lift and tell you which section is affected. If the car is also due for brake pads or discs, doing it all in one visit saves on bleeding and labour. And if the underside of the car had a general corrosion advisory too, the underbody corrosion guide explains what to watch.
Got a few advisories to work through? The MOT advisory decoder sorts them by urgency for you.
Got more than one advisory?
Paste your whole MOT result into the decoder. It explains every line, sorts them by urgency and adds up a rough repair budget.
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