Lipped or Scored Brake Discs: Do They Need Replacing?

Written by Petro Olekhnovych, mobile mechanic in Aylesham, Kent

Lipped brake discs do not always need replacing, but a lip is a sign the disc has worn and should be measured. A disc must be replaced once it reaches the minimum thickness stamped on it, or if it is deeply scored, cracked, badly corroded or overheated. Only a measurement tells you for sure.

Here is how to tell normal wear from a disc that has had its day, and why it matters when you fit new pads.

What is a lip on a brake disc?

Your brake pads squeeze the disc to slow the car. Over time this wears the disc down as well as the pads. Brembo, the brake manufacturer, points out that the same process that wears the pads also wears the disc.

As the braking surface wears, a raised rim builds up around the outer edge of the disc. That rim is the lip. You can often feel it by running a finger around the edge of the disc (only when the car is parked and the brakes are cold).

A lip tells you the disc has worn. It does not tell you how much metal is left. A disc with a small lip may still be well within its limit. A disc with a large lip may already be too thin.

Do lipped brake discs need replacing? Check the minimum thickness

Every disc has a minimum thickness set by the manufacturer. HELLA and Brembo both say this figure is usually stamped on the disc in millimetres, marked “MIN TH”. Your service manual will also list it.

To check it properly, a mechanic measures the disc with a suitable gauge. Brembo recommends measuring in at least four places around the disc and using the lowest reading.

The rule is simple:

• Above the minimum: the disc can stay, as long as it is not damaged in other ways.
• At or below the minimum: HELLA says the disc must be replaced.

Brembo explains why thin discs are a problem. A thinner disc holds less heat and is weaker, which can lead to cracks, distortion and a longer pedal travel.

What about scored brake discs?

Scoring is the pattern of grooves or lines on the shiny braking surface. Bosch says it is caused by dirt particles getting between the pad and the disc. It can lead to brake noise, rubbing and reduced braking performance.

Not all scoring is a problem:

• Light marks are normal. EBC Brakes and Autopartspro both say light surface scoring from normal wear is acceptable.
• Deep grooves are not. They reduce braking performance and wear new pads faster.

A quick guide from Autopartspro: run your fingernail across the disc. If your nail catches in the grooves, the scoring is too deep to keep using the disc.

Other signs your brake discs need replacing

Thickness and scoring are not the only checks. Bosch lists several other kinds of disc damage:

• Rust on the braking surface. Road salt, cleaning products and long periods without use can corrode the disc. This can cause noise and uneven braking.
• Blue patches. These point to overheating, for example from a sticking caliper or a binding handbrake. Bosch advises checking the whole brake system, not just swapping the disc.
• Uneven wear. This can cause vibration through the steering wheel and a pulsing brake pedal.

Autopartspro adds that vibration through the pedal under moderate or heavy braking often points to uneven disc thickness.

If your brakes grind, vibrate badly, pull to one side or take longer to stop the car, do not keep driving. Get them checked first. Our guide to brake pad warning signs covers the noises and symptoms to watch for.

Can you fit new pads on lipped discs?

Only if the discs are still above their minimum thickness and in good condition. HELLA says new pads should only be fitted if the disc’s minimum thickness has not been passed.

If the discs are worn, scored or below the minimum, EBC Brakes says new pads should be fitted at the same time. Fitting new pads to badly worn discs can reduce performance, cause noise and shorten the life of the new pads.

Two more rules from the manufacturers:

• Replace discs in pairs. HELLA and Brembo both say to replace the discs on both sides of the axle, even if only one is worn out.
• New discs, new pads. Bosch advises always fitting new pads when you change the discs.

For a breakdown of what affects the price of the job, see our post on brake pads and discs cost.

Will lipped brake discs fail an MOT?

Not automatically. The MOT inspection manual lists a brake disc that is “significantly and obviously worn” as a major defect, which is a fail. But it also tells testers that a disc must be significantly worn before they reject it.

So a small lip on its own is unlikely to fail an MOT. That does not mean the disc is fine. A disc can pass the test but still be close to its minimum thickness. Other disc faults are treated more seriously:

• Disc contaminated with oil or grease: major
• Disc insecure, fractured or otherwise likely to fail: dangerous
• Disc missing: dangerous

How we can help

We replace brake pads and brake discs at your home or workplace. We will measure your discs, check for scoring and other damage, and tell you honestly whether they need replacing or can stay. We are based in Aylesham and cover Canterbury, Dover, Deal, Sandwich, Folkestone and the villages around them. You can find your town on our areas we cover page.

Our labour is £30-£50 per hour depending on the job and its difficulty. Parts are extra, and we agree the price with you on WhatsApp before any work starts.

Frequently asked questions

Is a lip on my brake disc normal?
A lip forms as the disc wears, so it is a sign of use rather than an automatic fault. The question is how thin the disc has become, which needs measuring.

Can lipped discs be skimmed instead?
Autopartspro says resurfacing can deal with minor imperfections, but severely scored discs need replacing. Any disc must stay above its minimum thickness.

Do I need to replace both discs?
Yes. Brembo and HELLA both say discs should be replaced in pairs on the same axle.

Should I change my pads when I change my discs?
Yes. Bosch recommends fitting new pads whenever you fit new discs.

Need help? Send a WhatsApp to 07563 350335 with your car’s make and model and we’ll come to you.

Sources

• HELLA Tech World: Testing the minimum thickness of a brake disc
• Brembo: Minimum brake disc thickness
• Bosch brake disc damage and causes guide (via Autobiz)
• EBC Brakes: Brake discs explained, when should you replace your brake rotors?
• Autopartspro: How to tell if brake discs need replacing
• GOV.UK: MOT inspection manual, section 1 Brakes