Brakes are the single biggest cause of MOT failures I see come through the door, and they're also the category where the wording confuses people most. A certificate can say your braking is 'imbalanced', that a disc is 'significantly worn' or that efficiency is 'below requirement', and none of that tells you which part is at fault.
Brakes are the single biggest cause of MOT failures I see come through the door, and they're also the category where the wording confuses people most. A certificate can say your braking is 'imbalanced', that a disc is 'significantly worn' or that efficiency is 'below requirement', and none of that tells you which part is at fault.
The MOT brake test is partly visual and partly measured on a roller brake tester. That matters, because a measured failure (efficiency or imbalance) is a number, not a diagnosis. It tells the tester the car isn't stopping properly; it doesn't tell anybody whether that's a sticking caliper, a contaminated pad, a collapsed flexi hose or a worn-out rear shoe.
Below are the brake failures and advisories that turn up most often, what each one normally means, and what I'd physically check before ordering a single part.
Brake pad(s) less than 1.5mm thick
The friction material left on at least one brake pad has been measured or judged below 1.5mm. That's the point where there isn't enough material left to guarantee the pad will still be doing its job before your next service, and it's also the point where the backing plate starts getting close to the disc.
Full explanation of Brake pad(s) less than 1.5mm thick
Brake disc significantly and obviously worn
The disc has lost enough thickness, or picked up enough scoring and pitting, that the tester judged it no longer fit for purpose. A pronounced lip around the outer edge is usually what triggers this — that lip is the original thickness, and everything inside it is what's worn away.
Full explanation of Brake disc significantly and obviously worn
Braking effort imbalanced across an axle
On the roller brake tester, one wheel on that axle produced noticeably less braking force than the other. It's a measurement, not a diagnosis — it says the two sides aren't matching, but it doesn't say why. In real driving this is what makes a car pull to one side under braking.
Full explanation of Braking effort imbalanced across an axle
Parking brake efficiency below requirement
The handbrake didn't generate enough braking force on the tester to meet the minimum required for the vehicle. Note that this is a measured result — a handbrake that feels fine on a flat driveway can still be well under the limit.
Full explanation of Parking brake efficiency below requirement
Brake fluid contaminated
The fluid in the reservoir was judged to be contaminated — usually dark, cloudy or visibly full of debris. Brake fluid absorbs moisture from the air over time, and moisture lowers its boiling point, which is what causes a long pedal after heavy braking.
Full explanation of Brake fluid contaminated
Brake pipe excessively corroded
A rigid brake pipe has corroded to the point where the tester judged its strength compromised. There's a real difference between surface rust, which is normal on an older car, and flaking corrosion that's eating into the wall of the pipe — this wording means the latter.
Full explanation of Brake pipe excessively corroded
Brake hose damaged, chafed or corroded
The flexible rubber hose that carries fluid from the hard pipe on the body to the moving caliper has been marked down. The tester bends and inspects each hose with the wheels on full lock, so faults that only show at an angle get found. Surface cracking is usually Minor; exposed reinforcement, a bulge under pressure or a badly corroded end fitting is Major or Dangerous.
Full explanation of Brake hose damaged, chafed or corroded
Brake binding
One brake isn't fully releasing, so it's rubbing all the time the car is moving. On the roller brake tester it shows as drag on a wheel that should be spinning free. Left alone it destroys pads and discs, eats fuel, and can get hot enough to boil the fluid at that corner.
Full explanation of Brake binding
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