The MOT Files

MOT defect file

Brake pipe corroded

Last updated

Quick answer

A rigid brake pipe has rusted. Light surface corrosion is an advisory, but a pipe that is excessively corroded or has been weakened is a failure, because it carries the pressure that stops the car.

Typical cost
£90–£250
DIY viability
Garage job
Sound and excessively corroded rigid brake pipes in sectionTwo rigid steel brake pipes are compared in longitudinal section. The sound pipe has a continuous, even wall around an open bore. The lower pipe has rust scale and several deep external pits; the deepest pit has removed most of the metal between the outer surface and the pressurised bore. That local wall loss makes the pipe likely to fail under hydraulic pressure, so excessive corrosion is an MOT failure.Sound pipeExcessive corrosion — failDeep pittingWall thinned by pittingPressurised boreLongitudinal section — wall loss is local, not uniform
A rigid brake pipe fails if it is excessively corroded, or corroded enough to be likely to fail under pressure. Pitting and wall loss are exaggerated here for clarity; light surface discolouration alone is not the same as serious structural corrosion.

What you might notice

  • Nothing at all in normal driving, which is what makes this one dangerous — it is found on inspection, from underneath
  • A pedal that slowly sinks towards the floor while you hold it at a junction
  • Damp or crusty rust staining along a pipe run, often where it passes over the rear axle or through a chassis clip
  • In the late stages, a pedal that suddenly drops to the floor and a brake warning lamp on the dashboard

What causes it

  • Winter road salt attacking the pipe where it sits inside a plastic clip and cannot dry out
  • Grit thrown up by the rear wheels blasting the protective coating off the underbody runs
  • Two dissimilar metals in contact, so the pipe corrodes faster where it meets a bracket or a union
  • Pressure washing the underside, which drives salty water into the clips rather than out of them

Advisory or failure?

The grading turns on how far the corrosion has gone. A pipe that is corroded but not seriously weakened is recorded as an advisory, so the car passes and you are told to keep an eye on it. A pipe that is excessively corroded, or corroded to the point of being seriously weakened, is a major defect and a failure. Any pipe actually leaking fluid, or so badly damaged that failure is imminent, is graded dangerous — which means the tester is telling you not to drive it away. Testers are instructed not to scrape or pick at pipes to prove a point, so the judgement is made visually and by feel.

Can you fix it yourself?

Garage job

Making up brake pipe is not beyond a competent home mechanic, but this job punishes shortcuts more than most. It needs a proper flaring tool that produces the right profile for your car, the correct pipe material, and a bleed afterwards that leaves no air in the system. The real traps are the unions: they seize solid into callipers and into the ABS block, and rounding one off turns a £120 job into a much bigger one. Most cars also need the pipe run copied exactly, because a pipe that touches a moving part will chafe through in a year. If a garage tells you one corroded pipe means the whole set, ask to see the rest — sometimes it is true, sometimes it is not.

What it costs

The pipe itself is inexpensive — a few pounds of tube and a couple of unions. This job is almost entirely labour, so the price tracks how awkward the run is: a short exposed length near a wheel might be £90 to £130, while a pipe that runs the length of the car under a fuel tank or heat shield sits at the top of the band. Cars with pipes routed above the subframe cost more again. A full set of pipes on a rusty older car can exceed £600, and at that point it is worth weighing against the value of the vehicle.

What happens if you ignore it

A corroded pipe does not weep gently and give you notice. It splits under pressure, usually the first time you brake hard, and the pedal goes to the floor. Dual-circuit systems mean you keep some braking on the other circuit, but stopping distances roughly double and the car pulls hard to one side. On the money side, a single pipe caught early is one of the cheaper brake jobs; left until the whole run is scaling, you are paying for the full set plus the labour to thread them through the underbody. Driving a car whose brakes are in that condition is also using a vehicle in a dangerous condition, which carries points and a fine quite separately from the MOT.

Common questions

Is a corroded brake pipe an MOT failure?
It depends how far the corrosion has gone. A pipe that is corroded but not seriously weakened is recorded as an advisory, so the car passes with a note. A pipe that is excessively corroded or seriously weakened is a major defect and a failure. One that is leaking, or so damaged that failure looks imminent, is graded dangerous.
How much does it cost to replace a brake pipe?
The pipe is only a few pounds of tube and a couple of unions, so you are paying for labour and access. A short exposed length near a wheel is roughly £90 to £130, while a pipe running the length of the car under a fuel tank or heat shield sits at £250. A full set on a rusty older car can exceed £600.
Can I drive with a corroded brake pipe?
Not once it has been graded dangerous. Corroded pipes rarely weep gently to give you warning; they split under pressure, usually the first time you brake hard. Dual-circuit systems leave you some braking, but stopping distances roughly double and the car pulls hard to one side. Using a vehicle in that condition also carries points and a fine.
Do all the brake pipes need replacing if one has corroded?
Not necessarily, though pipes on the same car have usually had the same exposure, so where one run is scaling badly the others often follow. Ask the garage to show you the remaining runs rather than take it on trust. Sometimes the full set genuinely is due, and sometimes only the length over the rear axle has suffered.
Why do brake pipes rust where they do?
Almost always where they cannot dry out. Winter road salt collects inside the plastic clips holding the pipe to the underbody, and grit thrown up by the wheels strips the protective coating off exposed runs. Corrosion also accelerates where the pipe meets a bracket or union in a different metal. Pressure washing the underside tends to drive salty water into the clips rather than out.

Cars this happens to most

Of every model with at least 2,000 tests in the DVSA data, these record brake pipe corroded on the largest share of their MOTs. Across all of them the typical rate is 1.7% of tests.

  1. Chevrolet Spark10%

    1,396 times in 13,364 tests

  2. Ford Fusion7.7%

    3,577 times in 46,353 tests

  3. Mitsubishi L2007.2%

    5,789 times in 80,366 tests

  4. Vauxhall Astravan7.1%

    442 times in 6,253 tests

  5. Suzuki Wagon R6.9%

    443 times in 6,444 tests

  6. Hyundai Matrix6.5%

    182 times in 2,809 tests

  7. Vauxhall Vectra6.5%

    1,428 times in 22,040 tests

  8. Renault Kangoo6.5%

    3,363 times in 52,135 tests

A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.

Pass rates for every make and model

Warning lights behind this

This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.

This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.

Has this been recorded on your car?

Check the full MOT history for any UK registration.

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