Squeaky brakes are one of the most common car noises, and one of the most annoying. Sometimes the squeal is harmless and disappears after a few stops. Sometimes it's your car telling you the pads are nearly finished.
The trick is working out which. Here are the usual causes, how to tell them apart, and what to do about each one.
Squeaking only in the morning or after rain
If the noise happens for the first few stops after the car has been parked overnight or in the rain, then goes away, it's almost certainly surface rust. Brake discs are bare cast iron, and a thin layer of rust forms on them within hours in damp weather. The pads scrape it off as you drive, which can squeak or grind briefly.
This is normal and nothing to worry about. If the noise stops after a few minutes of driving, you can ignore it.
A high-pitched squeal every time you brake
Many brake pads have a small metal tab called a wear indicator. When the pad material gets thin, the tab touches the disc and makes a high-pitched squeal. It's designed to be annoying, so you notice it.
If the squeal starts happening every time you brake, and it doesn't go away after a few stops, check your pad thickness. On many cars with alloy wheels you can see the pad through the wheel. If the friction material looks thinner than about 3mm, it's time to replace the pads.
Grinding rather than squeaking
A harsh grinding or scraping noise is more serious. It usually means the pad material has worn right through and the metal backing plate is rubbing on the disc. That destroys the disc quickly and seriously reduces braking. Get the car checked as soon as possible, and don't drive it further than you need to.
Grinding can also be caused by a stone trapped between the disc and the dust shield behind it. That can sound alarming but is usually easy to fix by a garage.
Squeaking after new pads have been fitted
New pads sometimes squeak for the first few hundred miles while they bed in to the disc. If the noise carries on after that, common causes include:
- Missing or worn anti-squeal shims on the back of the pads
- No brake grease on the contact points between the pad and the caliper
- New pads fitted to old, glazed or uneven discs
- Pads with a hard compound, which tend to be noisier
Cleaning the contact points and applying a thin layer of the right brake grease to the back and edges of the pads, never the friction surface, often solves it.
Glazed pads or discs
Heavy braking, especially down long hills or when towing, can overheat the pads and leave a hard, shiny glaze on the pad and disc surface. Glazed brakes often squeal and don't grip as well. Lightly sanding the pads can sometimes help, but badly glazed or blue-tinged discs usually need replacing.
A sticking caliper
If one brake is dragging, the pad stays in constant contact with the disc, which can cause squealing, a burning smell and a hot wheel. Our guide to a sticking brake caliper explains how to check for it.
Squeaking when you're not braking
A squeal that happens while driving and stops when you press the brake is often the wear indicator just starting to touch the disc. It can also be a bent dust shield rubbing on the disc, or a dragging caliper. A squeak that changes with steering or bumps may not be the brakes at all and could be suspension or a wheel bearing.
When to get it checked
Book the car in promptly if the noise:
- Happens every time you brake, whatever the weather
- Has turned into a grinding sound
- Comes with a brake warning light on the dashboard
- Comes with vibration, pulling to one side or a soft pedal
At an MOT, pads worn down to the wear indicator are a major defect, and pads worn below 1.5mm are classed as dangerous.
Replacing pads and discs
Pads and discs are always replaced in pairs across an axle, so both fronts or both rears together. If the discs are smooth and above their minimum thickness, new pads may be enough. If they're scored, lipped or vibrating, replace both. Our guide to worn brake discs and pads covers what to look for and what affects the cost.
We stock a wide range of brake pads, discs, calipers and sensors for most popular makes. Brake parts are specific to the model and sometimes the trim, so match the part number on your old parts, or send us your VIN and we'll help you find the right ones.
This article is a general guide only. Brakes are a safety-critical system. If you're unsure, have them checked by a qualified mechanic.