Brake Discs and Pads: UK Buying & Safety Guide

Brakes are the one area of a car where “near enough” is never good enough. Yet replacement discs and pads are among the most commonly bought parts online, often by drivers who are not entirely sure what they need. This guide explains what the MOT really checks, how to tell when discs and pads are worn, what the law says about replacement pads in the UK, and how to make sure you buy the right parts.

What the MOT checks on pads and discs

The DVSA’s MOT inspection manual for cars and light vans sets out exactly how testers judge brake pads and discs.

Brake pads (section 1.1.13). The manual explains that some pads have metal wear indicators that squeal against the disc when the pad is badly worn, while others have a cut or groove that disappears when the pad needs replacing. The defects are:

“Brake lining or pad worn down to wear indicator”: major
“Brake lining or pad worn below 1.5mm”: dangerous
“Brake lining or pad contaminated with oil, grease etc.”: major
“Brake lining or pad missing or incorrectly mounted”: dangerous

Interestingly, the manual also states that “An illuminated brake wear indicator is not a reason for failure.” In other words, the dashboard light alone won’t fail the car, but the tester will still inspect the pads, and a pad down to its indicator will.

Brake discs (section 1.1.14). Here the manual takes a deliberately cautious line: “A brake disc or drum must be significantly worn before you should reject it. Being worn below the manufacturer’s recommended limits is not a reason in itself.” The defects are “Brake disc or drum significantly and obviously worn” (major), “insecure, fractured or otherwise likely to fail” (dangerous), contaminated with oil or grease (major), and missing (dangerous).

That second point is important. Passing the MOT does not mean your discs are within the manufacturer’s limit. The MOT is a minimum standard on the day, so disc thickness is something you or your garage should check yourselves.

How to check disc wear properly

Most discs have their minimum thickness stamped on them. Lighting and parts maker Hella explains that the manufacturer’s minimum thickness is the wear limit of the disc, stamped in millimetres on the outer edge or on the disc’s central chamber, and marked “MIN TH”.

Brembo’s guidance on measuring it is straightforward:

Use a vernier caliper or a proper brake disc gauge.
Measure in at least four different places around the disc.
Use the lowest reading as the figure for the whole disc.
If it is below the MIN TH value, the disc must be replaced.

Brembo also warns that an over worn disc can’t get rid of heat as well and is mechanically weaker. It lists the results as thermal cracks on the braking surface, distortion that causes vibration and noise, longer pedal travel and, under heavy use, brake fade.

Two rules come up in both Brembo’s and Hella’s guidance:

Replace discs in pairs. Both discs on an axle should be changed together, even if only one is below the limit.
Don’t put new pads on worn discs. Hella advises only fitting new pads if the disc has not gone below its minimum thickness.

Brembo adds a useful rule of thumb: as a general rule, discs should be replaced at every other pad change. Your car’s own service schedule and a measurement always take priority.

What the law says about replacement pads

This is the part many buyers don’t know about. The Road Vehicles (Brake Linings Safety) Regulations 1999 control which replacement brake linings can be supplied and fitted in the UK.

For cars, light vans and minibuses up to 3.5 tonnes (categories M1, M2 and N1), the regulations as made say that replacement brake linings must be either type approved under the European braking devices directive, or approved under ECE Regulation 90 (in its 90.01 version), and marked and packaged as those rules require. This applies to vehicles first used on or after 1 September 1999. For older vehicles, the replacement linings must not cause the car to fall short of the braking rules that applied when it was first used.

The same regulations ban supplying or fitting brake linings that contain asbestos.

In practice, this means you should buy pads from a recognised brand or supplier and check the box for the approval marking. ECE R90 approved pads carry an approval marking on the packaging. A suspiciously cheap set with no markings and no brand is not worth the risk.

How to make sure you buy the right parts

Brake parts vary far more than most people expect. The same model can have different disc sizes depending on engine size, trim level, whether it has a sport pack, and even the date it was built. Before you order:

Use your registration and VIN. A reputable supplier will match parts to your exact car rather than just the model name.
Check disc diameter and type. Measure the old disc’s diameter and note whether it is solid or vented (two faces with cooling vanes between them).
Check for wear sensor wires. If your pads have a wear sensor lead, make sure the new set has the same, or that a new sensor is included.
Read the existing part numbers. Discs and pads often have part numbers stamped or printed on them. These are the most reliable way to match.
Buy axle sets. Pads come in axle sets, and discs should be bought as a pair.

When fitting, Brembo stresses following the manufacturer’s specifications, using a torque wrench and the correct tightening sequence. If you are not confident, this is a job for a garage.

New or used?

Pads are a wear item, so they should always be new. Discs are usually bought new too, because a used disc may already be close to its limit. Other braking parts, such as calipers, backing plates or ABS sensors, are sometimes sourced used or reconditioned for older cars, especially when new ones are hard to find. Services such as Spare Car Part can help track down new or used brake components from UK suppliers using your registration and part numbers. Whatever you buy, have the finished job checked if you have any doubts.