The signs you hear and feel
The first signal is usually a sharp metallic squeal under light braking: the mechanical wear indicator, a tab fitted to the pad, has begun touching the disc. It is a warning designed to appear a few thousand kilometres before the real limit. Many cars use an electrical sensor instead, which lights a warning on the dashboard.
A dull metallic grinding sound, present even when you are not braking, means the friction material is completely used up and the pad's steel backing is rubbing directly on the disc. At that stage the disc is ruined within a few dozen kilometres and stopping distances grow noticeably. Vibration through the pedal or the steering wheel when braking from speed usually points to disc thickness variation.
When to replace the pads
A new pad carries roughly 10–12 mm of friction material. The practical replacement limit is 3 mm of material left above the steel backing: below that, the ability to shed heat drops and the risk of reaching metal between two inspections becomes real.
Pads are replaced as a set, on both wheels of the same axle. Fitted on one side only, they brake unevenly and pull the car sideways. While you are there, check the caliper boots, the guide pins and the condition of the brake hoses.
When to replace the discs
Every disc has the minimum permitted thickness stamped on the hub or the edge, usually marked “MIN TH”. Once a micrometer reading reaches that figure the disc is replaced — it can no longer be skimmed. Discs are also replaced in pairs, on the same axle.
Replacement is also needed before the minimum thickness if the disc shows radial cracks, deep grooves, heavy corrosion of the friction face after long standing, or lateral run-out felt as a pulsation in the pedal. Bluish patches indicate overheating: the material's structure has changed and braking becomes unpredictable.
Bedding in after replacement
New pads and discs need an even transfer layer of friction material on the disc surface. Perform 20–30 moderate stops from about 60 to 30 km/h with cooling pauses in between, and avoid violent braking for the first 200 km.
Do not park with the handbrake applied straight after heavy braking while the discs are hot: the pad pressed against the disc leaves a material imprint that is later felt as a pulsation. Check the brake fluid at the same time — it is hygroscopic and is normally replaced every two years.
Symptom, likely cause and what to do
| Symptom | Likely cause | What to do |
|---|---|---|
| Sharp squeal under light braking | Wear indicator touching the disc | Book the pads in for replacement |
| Constant metallic grinding | Friction material completely used up | Stop driving and replace pads and discs |
| Pulsation through the pedal | Disc thickness variation or run-out | Measure the disc; it usually needs replacing |
| Car pulls to one side when braking | Seized caliper or unevenly worn pads | Check the caliper and the guide pins |
| Soft pedal with long travel | Air or moisture in the circuit | Check and replace the brake fluid |
How to check brake wear yourself in 4 steps
A visual check that takes a few minutes with the car stopped and the brakes cold, in most cases without removing the wheel.
- 1
Make the car safe
Park on level ground, apply the handbrake and wait for the brakes to cool completely. If you raise the car, always use axle stands, never the jack alone.
- 2
Look at the pad through the wheel spokes
On most wheels the edge of the outer pad is visible. Compare the thickness of the friction material with the steel backing: if the layer looks thinner than 3 mm, the pads are at their limit.
- 3
Inspect the disc surface
Run a gloved finger across the friction face. A pronounced lip at the outer edge shows accumulated wear, while deep grooves, radial cracks or bluish patches mean replacement.
- 4
Check the brake fluid level
A slowly falling level with no visible leaks is normal as the pads wear. A sudden drop indicates a loss in the circuit and calls for immediate inspection at a garage.
Frequently asked questions
Can I replace only the pads, not the discs?
Yes, if the discs are above minimum thickness, free of cracks and without run-out. On an unevenly worn surface, though, new pads bed in poorly and braking stays weak for a few hundred kilometres.
How long does a set of brake pads last?
Roughly 30,000 to 60,000 km, depending on driving style, the weight of the car and the type of route. Urban driving with frequent stops can halve that compared with out-of-town mileage.
Why do new brakes squeal?
For the first few hundred kilometres, until the transfer layer forms, an occasional squeal is normal, especially in damp weather. If it persists, check that the anti-rattle shims are fitted and the guide pins are greased.
The information in this guide is indicative. Always follow the intervals and specifications given in your own car's owner's manual.
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