Brake noise is one of the most common reasons people bring their car to a workshop. Some sounds are harmless, others mean the pads are worn out.
Sounds and what they mean
- A high squeal that disappears after a few stops: often moisture or light surface rust on the discs after a night outside. Normal.
- A constant high-pitched squeal when braking: the wear indicator (a small metal tab) is touching the disc – the pads will need replacing soon.
- Metallic grinding or scraping: the pads are completely worn and metal is rubbing on the disc. Dangerous – stopping distances increase and the disc gets damaged.
- A clunk at the start of braking: a loose pad or caliper, or worn guide pins.
- Steering wheel vibration when braking: warped or unevenly worn brake discs.
- The car pulls to one side when braking: a sticking caliper or uneven wear.
What you can check yourself
- Look through the wheel: the pad friction material should be at least 3 mm thick.
- Is there a sharp raised lip on the edge of the disc? That indicates wear.
- Is one wheel much hotter than the others after a drive? Possibly a sticking caliper (careful – it can be very hot).
- Check the brake fluid level – it drops slightly as the pads wear.
Repair
Pads and discs are always replaced in axle pairs (both fronts or both rears). When replacing them, the guide pins should be cleaned and greased and the calipers checked. New pads need bedding in: avoid hard stops for the first 200 km or so.
Don't forget the fluid
Brake fluid absorbs moisture over time, which lowers its boiling point and corrodes the system from inside. It should usually be replaced every two years, regardless of mileage.
Rust after the car has stood still
Cars that are driven rarely often get a rust ring on the discs and noisy, uneven braking. A few firm stops can clean them, but heavily pitted discs need replacing.
Describe the noises in Diagno's AI diagnosis, and have a trusted mechanic inspect the brakes – they are not worth gambling on.