Brakes are the one system on a car where "it still works" is not the standard. Everything else gives you warning and a second chance; brakes give you the distance you have and nothing more. The useful thing about them is that they degrade predictably, and every stage announces itself — if you know what you're listening for.
| What you notice | Usual cause | What it needs |
|---|---|---|
| Squeal that stops under braking | Pads at the wear indicator | Pads, both sides of the axle |
| Grinding under braking | Pads finished, backing plate on the disc | Pads and almost certainly discs |
| Pedal pulsing, steering shimmy when slowing | Uneven disc thickness | Discs in pairs, with new pads |
| One side wearing far faster | Seized caliper or slide pins | Fix the caliper first — new pads alone will wear the same way |
| Soft or sinking pedal | Fluid, hose or seal | A hydraulic repair; pads won't change it |
The fourth row is the one that costs people twice. If a caliper is sticking, fitting new pads buys you a few months of the same problem and a second set of pads.
Pad friction material starts somewhere around 10–12 mm on most cars and is generally considered finished at about 3 mm — measured on the material, not including the steel backing plate. Below that you are into the range where heat management falls away before the material physically runs out.
Discs carry their own limit, and it is stamped on them: a minimum thickness marked on the hub face or the outer edge. A disc under that figure is scrap regardless of how it looks, because the remaining metal can no longer absorb the heat of a hard stop. Measure rather than eyeball — a disc with a visible lip at the outer edge has usually already lost more than it appears to.
| Material | Suits | Trade-off |
|---|---|---|
| Organic (NAO) | Light city driving, quiet operation | Wears fastest and fades soonest under sustained heat |
| Semi-metallic | Heavier cars, loads, long descents | Noisier when cold, more dust, wears the disc harder |
| Ceramic | Quiet running, clean wheels, long pad life | Costs more; less bite before it warms up |
For most cars in ordinary use the honest answer is the specification the manufacturer chose. Move away from it deliberately — towards semi-metallic if the car is regularly loaded or descending long grades, towards ceramic if you want quiet and clean wheels — not because a box on a shelf promised performance.
New pads and discs need bedding in: a series of moderate stops from moderate speed, letting the brakes cool between them, before any hard use. Skipping it is the most common reason a fresh set starts juddering within weeks. And while the wheels are off, ask for the brake fluid to be checked — it absorbs moisture over time, and old fluid lowers the temperature at which the pedal goes soft under repeated braking, no matter how new the pads are.
Browse car parts, and see our maintenance schedule for where brake inspection sits alongside the rest of the service intervals.
Squeal means soon; grinding means now and probably discs too. Fix a sticking caliper before fitting pads or you will buy pads twice. Replace by axle, match by part number rather than model year, respect the minimum thickness stamped on the disc, and bed new brakes in before you need them.
A thin metallic squeal that stops when you brake is the wear indicator touching the disc — the designed warning, meaning soon rather than now. A grinding sound while braking means the friction material is gone and metal is on metal, and every stop from then on is also cutting the disc.
When the pedal pulses or the steering shimmies as you slow down — that is uneven disc thickness. Once you reach grinding, the discs are almost certainly damaged too. And any disc below the minimum thickness stamped on it is finished regardless of how it looks.
Friction material starts around 10–12 mm on most cars and is generally considered finished at about 3 mm, measured on the material itself and not the steel backing plate. Discs carry their own minimum thickness, stamped on the hub face or the outer edge.
Usually a seized caliper or sticking slide pins. This is the fault that costs people twice: fitting new pads without fixing the caliper buys a few months of the same problem and a second set of pads.
For most cars in ordinary use, the specification the manufacturer chose. Move away from it deliberately — semi-metallic if the car is regularly loaded or descending long grades, despite the noise and dust; ceramic for quiet running and clean wheels, despite the cost and the weaker bite before it warms up.
Bed them in: a series of moderate stops from moderate speed, letting the brakes cool between them, before any hard use. Skipping it is the most common reason a fresh set starts juddering within weeks. And have the brake fluid checked while the wheels are off.
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