Car brakes: how to tell they need changing before they fail

Of every part on a car, brakes are the most critical. You can drive with the aircon broken, a loose seat or a silent radio. Brakes don't allow shortcuts. A serious braking failure at 100 km/h isn't fixed by reflexes — you pay for it dearly.

The good news is that brakes warn you. They almost always give signs for weeks or months before they actually run out. The problem is that most drivers don't recognise those signs until it's already an emergency.

How pads and discs work

Disc brakes are simple: when you press the pedal, brake fluid pushes pistons that squeeze two pads against a metal disc that spins with the wheel. The friction between pads and disc is what slows the car down and turns motion into heat.

The pads are made from a material that wears down on purpose: they're a sacrificial part. The discs last longer, but they wear too and warp with use, especially after hard braking with the disc very hot.

5 signs it's time for new pads

• Sharp metallic squeal under light braking: most modern pads have a small metal tab that scrapes the disc when the friction material hits minimum. It's a deliberate warning from the manufacturer.
• Softer or longer pedal than usual: if you find yourself pressing further to get the same braking, get it checked.
• Longer stopping distance: if you've started to brake earlier than you used to, your brain has already told you something even if it wasn't conscious.
• Brake warning light on the dashboard: modern cars have a sensor that flags wear on the display. Don't ignore it.
• Mileage: as a rule, front pads last between 30,000 and 60,000 km, depending on the car and driving style. If you're beyond that with no change, check them.

3 signs it's time for new discs

• Visible grooves on the disc surface: if you can see circular grooves in the metal from outside, the disc is worn. In some cases they can be skimmed; usually they're replaced.
• Vibration in the pedal under braking: if the pedal shudders or the steering wheel shakes under hard braking, the disc is warped. Replacement is not optional.
• Below the minimum thickness: every disc has a minimum thickness stamped on the part itself. If a caliper gauge reads below that, it's replaced without discussion — that's not optional, that's safety.

Front vs rear brakes

The front axle does 70% of the braking, because weight transfers forward as you brake. That's why front pads and discs wear out much faster than the rears. It's normal to change fronts twice for every one time you change rears.

In modern cars, many rear brakes are drum, not disc. The principle is the same (friction to slow down), but wear is even slower and the maintenance is different. On a proper brake inspection we evaluate all four wheels separately.

Brake fluid counts too

Brake fluid absorbs moisture over time. With moisture in it, it boils at a lower temperature, and during hard braking on a long descent it can actually vaporise. When brake fluid vaporises, the pedal sinks and doesn't brake. It's called "fading" and it's one of the most dangerous things that can happen on the road.

That's why brake fluid is changed every 2 years, even if the car barely moves. It's a cheap job that prevents a very expensive problem.

This is not a check you can postpone

A bald tyre lets you drive slowly to the workshop. Pads at minimum or warped discs? Every kilometre is a risk. If you spot any of the signs in this article, don't wait until the weekend.

At Salpe the brake inspection is free: we measure the pads, check the discs, look at the fluid and adjust if needed. We tell you exactly what needs replacing now and what will last a few more months. You can book online or drop by the workshop any weekday morning.

— The Salpe Team