Brake wear: the noises that arrive before the bill does

A new brake pad carries roughly 10 to 12 mm of friction material. By about 3 mm it is due for replacement. At 0 mm the steel backing plate is pressing straight on the disc, which stops the car badly, ruins the disc, and turns a routine pad change into a pads and discs bill.

Unlike a tyre, you rarely look at a brake pad. So the system is designed to be heard instead, and the sounds arrive in a fixed order.

The sequence of sounds, in order of urgency

Sound	What it is	Urgency
High squeal that stops when you brake	The wear indicator, a small steel tab set to touch the disc when the pad reaches its limit	Book the change now
Squeal while braking	Glazed pads, dust between pad and disc, or the indicator fully engaged	Inspect this week
Grinding, metal on metal	Friction material gone. The backing plate is cutting into the disc	Stop driving on it
Pulsing or judder through the pedal	Uneven pad deposits or a warped disc, usually after hard use or standing water on hot discs	Inspect soon, it gets worse

Discs wear too, and theirs is a hard number

Every disc has a minimum thickness cast or stamped into its hub or edge. A workshop measures it with a micrometer across the friction face, not at the outer lip, where an unworn ridge hides the loss. Below that minimum a disc can overheat, warp, or crack, and no new pad fixes that.

There is one honest tell you can read yourself: the ridge at the disc's outer edge. That lip is the difference between the original surface and what braking has removed, so a deep lip means the disc has already given up a lot of its thickness.

Checking pads without removing the wheel

• Look through the wheel spokes at the caliper. On most cars the outer pad's edge is visible against the disc, and what you are estimating is the thickness of material left between the metal plate and the disc face.
• Compare left against right. One side markedly thinner usually means a sticking caliper slider, and the fix is servicing the caliper rather than just fitting new pads.
• Watch the brake fluid level. It falls slowly as pads wear because the calipers hold more fluid. A level near minimum with no leak often just means the pads are finished, and topping it up hides the message.
• Note pulling to one side under braking. That is one wheel braking harder than its pair. Suspect a caliper or pad problem before you blame alignment.

Why city traffic eats brakes

Pad life quoted by makers assumes mixed driving. Stop-start traffic, hills and heat all shorten it. A car that lives in dense city driving can use pads at twice the rate of the same car on open roads. Dust matters too, because fine grit between pad and disc speeds up wear on both, and it is behind a lot of the persistent squeal you hear in dry, dusty conditions.

So track pad life against your kilometers, not the brochure's. Two pad changes logged with odometer readings will tell you your real interval better than any table.

Common questions