Grinding, a soft pedal or a brake light? Don't drive on
Grinding can mean the pads are worn down to the metal, and a soft or sinking pedal can mean a fluid leak. AA New Zealand says a significant brake fluid leak may stop the car braking properly. Pull over somewhere safe, switch off and have help come to the car. If anyone is hurt or in danger, call 111.
When does the squeal happen?
| Likely cause | What to do | |
|---|---|---|
| First few stops on a cold, damp morning | Moisture and a film of rust on the discs | Nothing, if it fades |
| After the car's been parked for weeks | Rust built up on the discs | Drive gently; have it checked if it stays |
| All the time, quieter when you brake | The wear indicator touching the disc | Get the pads checked this week |
| At low speed, soon after new pads | Pads and discs that don't suit each other, or not bedded in | Back to the garage that fitted them |
| A sudden scrape after a gravel road | A stone caught by the disc | A short reverse may shift it; if not, a mechanic |
| Grinding or metal on metal | Pads worn out | Stop driving and get help |
Why do brakes squeal at all?
Most squeal is vibration. Wikipedia's disc brake entry says the pads and discs can set up a high-pitched vibration, that cold weather and morning dew make it worse, and that this kind of squeal shouldn't affect how well the car stops. Brake dust can add to it.
The squeal that matters is the deliberate one. Many pads carry a small metal tab that rubs on the disc once the pad is nearly worn through. AA New Zealand notes the noise is usually loudest when you're not braking and may ease off when you are. Mazda's owner's manual puts it plainly: when you hear it, the pads need replacing.
Ignore it, and AA New Zealand warns you risk ruining the discs, and a worn pad can work loose.
Can you just clean squeaky brakes?
Sprays are sold as a quick cure, but brakes aren't a home job. Anything sprayed in the wrong place can reach the pads and discs and cut their grip. If the squeal stays, the fix is usually new pads, sometimes discs, and occasionally shims or anti-squeal paste behind the pads, all done by a mechanic.
Before you ring a mechanic
Listen with the window down
Note whether it squeals all the time, only when you brake, or only when cold.
Work out which corner
Front or back, left or right, if you can tell.
Look at the wheels
Heavy black dust on one wheel and not the others is worth mentioning.
Feel the pedal
Firm and high is good. Soft, low or pulsing changes how soon it needs seeing.
What the mechanic will check
Pad thickness on every wheel, the discs for scoring and wear, the calipers for sticking, and the brake fluid. They should tell you how much pad is left, or show you.
Don't count on the WoF to catch thin pads. The MTA says pad thickness isn't part of the inspection unless the pads are visibly below safe limits, though the inspector does check how the brakes work. A fresh WoF doesn't mean the pads have long left.
What you can do, and what to leave to the mechanic
You can
- Listen, and note when it squeals and from which corner.
- Notice any change in how the pedal feels.
- Reverse a short way if a stone seems caught after a gravel road.
Leave to the mechanic
- Taking wheels off and measuring pads and discs.
- Replacing pads, discs, shims or fittings.
- Brake fluid checks and any caliper work.
What we'd do
A squeal that's gone after the first few stops on a damp morning, we'd ignore. A squeal on every drive, we'd have checked within the week and ask for the pad thickness in writing. Grinding, we'd stop for.