Is a brake disc below its minimum thickness an MOT failure?

Yes, it is a major defect. The judgement is separate from surface condition, so a disc can look smooth and clean and still be too thin, or be visibly scored and still be thick enough. Where the disc is so worn, cracked or insecure that failure is imminent, or it is fractured or missing a section, the grade is dangerous.

How do I know if my brake discs are too thin?

The minimum figure is cast or stamped into the disc itself, usually on the edge or the hub face, and you measure the swept area against it with a micrometer or vernier. Without tools, the giveaway is a pronounced lip of rust or unworn metal around the outer rim, with the braking surface sitting well below it.

Can thin brake discs be skimmed instead of replaced?

No. Skimming removes metal, so a disc already at or below its minimum cannot be machined back into specification, and doing so leaves even less material to absorb heat. Skimming only ever applies to a disc with thickness to spare, and on ordinary road cars a new pair usually costs less than the machining anyway.

Do brake discs have to be replaced in pairs?

Replace them across the axle. A new disc on one side and a worn one on the other gives different friction and different heat behaviour, so braking is no longer even. It matters for budgeting too: if a seized calliper or overheating has ruined one disc, price the job as two, because the pair goes together.

How much does it cost to replace brake discs and pads?

Front discs and pads for a common hatchback are £90 to £180 in parts with about an hour and a half of labour, so £200 to £320 fitted is typical. Rears with an electronic parking brake push towards £480. Nothing hydraulic is opened, so it is achievable at home if you have axle stands and a torque wrench.

MOT defect file

Brake disc below its minimum thickness

Last updated 27 July 2026

Quick answer

The disc is no longer thick enough. This is not the same as the scoring and pitting recorded as surface wear — the metal itself has gone past the limit stamped on it by the manufacturer, and no amount of new pads will fix that.

Typical cost: £200–£480
DIY viability: Possible with care

A disc fails the MOT if it is significantly and obviously worn, or worn below the minimum thickness stamped on it by the manufacturer. The raised lip at the edge is the original thickness, which is why running a fingernail across it tells you how much has gone. Wear exaggerated for clarity.

What you might notice

A pronounced lip of rust or unworn metal around the outer edge of the disc, with the swept face sitting well below it
Brakes that have needed pads unusually often, because a thin disc sheds heat poorly and cooks the material
Juddering through the pedal or the steering wheel under moderate braking as the thin disc distorts with heat
A metallic grinding once material runs out entirely, which by then means the damage is done

What causes it

Two or three sets of pads fitted over the years without anyone measuring the disc underneath
Cheap pads with an aggressive friction compound that wears the disc faster than the pad
Corrosion pitting the surface, so each set of pads has to grind away sound metal to bed in
A previously seized calliper wearing one face of the disc much harder than the other

Advisory or failure?

A disc worn below the minimum thickness specified by the manufacturer — the figure cast or stamped into the disc itself — is a major defect and a failure. This is a separate judgement from surface condition: a disc can be smooth and clean and still be too thin, and it can be visibly scored and pitted while remaining thick enough. The grade rises to dangerous where the disc is so worn, cracked or insecure that failure is imminent, and a disc that is fractured or has a section missing is dangerous regardless of thickness. Testers assess this without dismantling anything, so the call is made on the visible wear lip and the state of the swept area.

Can you fix it yourself?

Possible with care

Discs and pads together are one of the more achievable brake jobs, because nothing hydraulic is opened. You need axle stands, a torque wrench, and often a hub-nut socket or a bearing puller depending on the design. Measure the old disc with a micrometer or vernier and compare it to the stamped minimum before you commit — the number is usually on the disc edge or the hub face. Replace discs in pairs across the axle so braking stays even, clean the hub face back to bare metal so the new disc sits true, and torque the wheel properly rather than leaning on a bar. On cars with a rear electronic parking brake, put the system into service mode with a diagnostic tool first. Copper grease belongs on the pad backing and the slider pins, never on the friction face.

What it costs

Front discs and pads for a common hatchback are £90 to £180 in parts, with an hour and a half of labour, so £200 to £320 fitted is typical. Rear discs on cars with an electronic parking brake cost more in both parts and time, pushing towards £480. What lifts a job to the top of the band is usually the hub: a disc rusted onto the hub face, a seized retaining screw, or a rear disc that also needs the parking brake shoes inside it. Premium or drilled and grooved discs cost considerably more, and on an ordinary road car buy you very little.

What happens if you ignore it

A disc past its minimum has lost the thermal mass it was designed with, so it overheats readily, warps, and can crack radially from the vent holes outwards. In the worst case the friction ring separates from the hub section under heavy braking, which removes that brake instantly and can lock the wheel. Long before that, you get fade on hills, juddering, and pads that wear out at twice the normal rate — so you end up paying for pads repeatedly rather than fixing the actual problem once. And since it is a major defect, the car cannot legally be used on the road until it is put right, with the usual roadworthiness exposure that comes with driving it anyway.

Common questions

Is a brake disc below its minimum thickness an MOT failure?: Yes, it is a major defect. The judgement is separate from surface condition, so a disc can look smooth and clean and still be too thin, or be visibly scored and still be thick enough. Where the disc is so worn, cracked or insecure that failure is imminent, or it is fractured or missing a section, the grade is dangerous.
How do I know if my brake discs are too thin?: The minimum figure is cast or stamped into the disc itself, usually on the edge or the hub face, and you measure the swept area against it with a micrometer or vernier. Without tools, the giveaway is a pronounced lip of rust or unworn metal around the outer rim, with the braking surface sitting well below it.
Can thin brake discs be skimmed instead of replaced?: No. Skimming removes metal, so a disc already at or below its minimum cannot be machined back into specification, and doing so leaves even less material to absorb heat. Skimming only ever applies to a disc with thickness to spare, and on ordinary road cars a new pair usually costs less than the machining anyway.
Do brake discs have to be replaced in pairs?: Replace them across the axle. A new disc on one side and a worn one on the other gives different friction and different heat behaviour, so braking is no longer even. It matters for budgeting too: if a seized calliper or overheating has ruined one disc, price the job as two, because the pair goes together.
How much does it cost to replace brake discs and pads?: Front discs and pads for a common hatchback are £90 to £180 in parts with about an hour and a half of labour, so £200 to £320 fitted is typical. Rears with an electronic parking brake push towards £480. Nothing hydraulic is opened, so it is achievable at home if you have axle stands and a torque wrench.

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.