How do I know when my brake pads need changing?

How to tell a harmless morning squeal from a worn-pad squeal from metal-on-metal, what a soft or long pedal is telling you, and the three symptoms that mean stop rather than book it in.

Difficulty: beginner
Time: 15 min
Read: 5 min
Safety: warning

Short answer

A short squeal on the first stop of a damp morning is surface rust being wiped off the discs and means nothing. A squeal that appears at every stop, or a rhythmic grinding, means the pads are at or past their limit — book it in now. A pedal that sinks slowly under steady pressure, or goes to the floor, is a hydraulic fault and means stop driving.

Brake pads are consumable by design: they are meant to wear away so the discs do not. What makes them confusing is that the noises they make cover an enormous range of seriousness, from completely normal to stop-the-car. Most cars now include a wear indicator — either a small metal tab that touches the disc and squeals when the friction material gets thin, or an electrical sensor that lights a dashboard warning. Neither is a countdown; both are a prompt that the job is due.

Safety

Brakes are safety-critical and this guide is diagnosis only. Do not attempt to change pads, discs or brake fluid unless you are trained and properly equipped — a mistake here has no second chance. A grinding noise, a pedal that sinks, a brake warning light or a strong smell of burning after braking all mean stop driving and get the car recovered rather than driven to a garage.

What a worn brake pad looks like, and what the squeal is

Step by step

Separate the morning squeal from the every-stop squeal.Discs rust lightly overnight in damp weather. The first two or three stops scrub it off with a squeal or a light grating, and it then goes away for the rest of the day. That is normal on any car left outside in Britain and needs nothing.
Listen for a squeal that is there at every stop, hot or cold.That is the classic worn-pad wear indicator: a thin metal tab designed to contact the disc when the friction material is nearly gone. It is doing exactly what it should. Book the car in — you have some time, but not much.
Treat a grinding or rhythmic scraping as urgent.Metal-on-metal means the friction material is gone and the pad backing plate is cutting into the disc. Every stop now costs you a disc as well as a pad, and braking performance is falling. Stop driving it beyond getting it to a garage.
Look at the pad through the wheel if you can see it.On many cars you can see the outer pad through the alloy spokes. You are looking at the thickness of the friction material against the metal backing plate. New pads have a substantial block of material; anything down to a few millimetres is near the end. Do not attempt to judge inner pads this way, and do not remove the wheel unless you know how to support the car safely.
Check what the pedal is telling you, because that is the more serious signal.A firm pedal that stops the car is fine even if the pads are worn. A pedal that feels spongy, that needs pumping, or that slowly sinks while you hold it at a junction points at air or a leak in the hydraulic system, which is a different and more serious fault.
Notice pulsing through the pedal or steering under braking.A rhythmic pulse that gets stronger the harder you brake is usually distortion or uneven deposits on the discs — often after a long descent, or after the car sat with hot brakes and the handbrake on. It is a comfort and wear issue rather than an immediate safety one, but it needs the discs looking at.
Give the garage the symptom, not just the request."Grinding from the front right when braking, started three days ago" gets you a better outcome than "can you check my brakes", because it tells them where to look and lets them tell you on the phone whether discs are likely too.

Common mistakes

Waiting for the grinding to stop — It does sometimes quieten as the backing plate wears a groove into the disc. That is the fault getting worse, not better, and by then the disc is scrap too.
Judging brakes by how the car feels rather than by noise and pedal — Modern servo-assisted brakes with ABS mask a lot of deterioration until it is severe. The noise arrives long before the feel changes.

If it doesn't work

Brake warning light on the dashboard

Cause: Could be low fluid, a pad wear sensor, or the handbrake not fully released — Fix: Check the handbrake is fully down first. If the light stays on, check the fluid reservoir level without opening it further than needed. Low fluid with worn pads is normal; low fluid with a wet patch anywhere is a leak, and that means stop.

Car pulls to one side under braking only

Cause: A seized caliper or sticking slide pin on one side — Fix: This is a garage job and worth prompt attention — a seized caliper drags, overheats, ruins the disc and can affect the car's stability under hard braking.

Strong hot smell after a long hill, brakes feel less effective

Cause: Brake fade from overheating — Fix: Slow down, let them cool, and on descents use a lower gear so the engine does the retarding. If it happens on ordinary driving, a caliper is likely binding.

Handbrake needs many more clicks than it used to

Cause: Cable stretch or rear pad wear — Fix: Mention it at the next service. It is also an MOT item, so it is better dealt with before the test than during it.

Squeal only when reversing

Cause: Pad vibration in the opposite direction of travel — Fix: Common and usually harmless, especially on newly fitted pads. If it develops into a squeal in both directions, treat it as wear.

Questions people ask

How long do brake pads last?

Anything from around 20,000 to well over 50,000 miles depending entirely on how and where you drive. A car doing motorway miles barely uses front pads; the same car in city traffic or on hills can go through them in a third of the distance. That variability is exactly why you judge by symptom rather than mileage.

Do discs have to be changed with pads?

Not always. Discs have a minimum thickness stamped on them and can often take a second set of pads. They do need replacing if they are below that minimum, scored by metal-on-metal contact, cracked, or badly corroded at the edges — which is common on a car that does low mileage in a damp climate.

Is it worth changing pads myself to save money?

This guide does not cover it, and the catalogue deliberately stops here. Pads look simple, but caliper piston retraction, correct torque, seized slide pins and electronic parking brakes all bite people, and the failure mode is not a leaky tap.