Squealing brakes: causes and what you should do

The most common cause of squealing brakes is wear of the brake pads, writes the ANWB. But it is not the only one. These are the five causes we see in the workshop:

1. The wear indicator: many brake pads have a small metal tab that touches the brake disc as soon as the lining is nearly gone. That tab gives a sharp, high squeal, often when you are not braking, and the noise stops the moment you press the pedal. It is a deliberate warning from the manufacturer: the pads are due for replacement. Some cars have an electric sensor instead of the tab, which turns on a warning light on the dashboard.
2. Dirt or surface rust on the discs: after a shower of rain, a car wash or a night outside, a thin layer of rust forms on the brake disc. Dust and dirt from the road do the same. The first few times you brake, the pad scrapes that layer off and you hear it as a squeal or a soft scraping sound. According to the ANWB, in many cases this disappears by itself after a few firm stops.
3. Fitting and anti-squeal shims: brake pads sit in the caliper with spring clips and often with a thin anti-squeal plate (shim). If those plates have been left out, reused or fitted incorrectly, or if the caliper slide pins are dry, the pad can vibrate slightly against the disc. That gives a high-pitched squeal. Brake manufacturer Brembo therefore says: do not reuse the old shim and grease the contact points between the caliper bracket and the pad with anti-squeal grease.
4. Low-quality brake pads: according to the ANWB, cheap or hard brake pads squeal more easily, especially at low speed and with light braking. The friction material itself starts to vibrate. Ferodo names vibration in the friction material as the most common reason for a high-pitched squeal.
5. New brakes that have not been bedded in: new brake pads and discs do not fit each other perfectly yet. The ANWB writes that the squealing then usually disappears by itself after a few hundred kilometres. Brake gently during that period and avoid hard emergency stops.

A sixth, less well-known cause is a brake caliper that does not release properly. If a pad keeps dragging lightly on the disc, you hear a squeal or a humming noise that follows the speed of the car, even without braking. You can read more about this in the article on a seized brake caliper.

The type of noise says a lot about how serious it is. A high, sharp squeal is usually a warning or a harmless vibration. A low grinding or scraping noise almost without exception means metal is running on metal, and that is the moment to stop driving. This is how you tell the difference:

Based on the ANWB explanation of squealing brakes and the fitting instructions from Brembo and Ferodo.

The grinding noise is the most serious. The ANWB warns that the brake discs cannot take it: the steel backing plate of the brake pad cuts grooves into the disc. What started as a set of brake pads then becomes a set of discs plus pads. It is also a checkpoint at the APK (MOT), the compulsory annual vehicle inspection in the Netherlands: the inspector turns the wheel by hand and, according to the RDW APK manual, no grinding noise of metal on metal may be audible. The RDW is the Dutch vehicle authority that sets the APK rules.

With a light squeal you can drive, with a grinding noise you cannot. The ANWB writes that squealing brakes are often harmless, but that the noise can point to a problem that needs attention. Use this rule of thumb:

Not sure? Call us and we will schedule a short brake check. If nothing needs doing, we tell you that too. We check the brakes at every service and every APK. If you hear other noises from under the car besides the squealing, have a look at car making a noise: there you will find the possible cause for each type of noise.

Yes. A short squeal after rain or after standing still is normal. A brake disc is made of cast iron and starts to rust lightly within one night. You can see that as an orange haze on the disc. The first few times you brake, the brake pad scrapes that layer off. You hear it as a squeal or a soft scraping, and sometimes you feel it as a slight catch in the pedal. After a few stops the disc is clean again and the noise is gone.

It is a different matter if the car has been parked for weeks or months, or if you make a lot of short trips with hardly any braking. Then the rust can eat deeper into the surface. The ANWB writes that surface rust is normally worn off by the brake pads, but that with little use the brake discs can become too badly affected. The pad then runs over a pitted surface and the squealing or scraping stays. In the article on rusty brake discs you can read when rust is harmless and when it is not. At the APK there is a limit: according to the RDW APK manual, on each side at least 50 percent of the width of the brake pad must have a smooth, non-corroded braking surface.

If the squealing continues after a day of driving, there is more going on than rust. In that case the ANWB advises having the brakes cleaned at a garage. We take the pads out of the caliper, clean the slide pins and the contact points, grease them again and assess whether the disc is still good enough.

On an electric or hybrid car the brakes squeal and grind more often because of rust, since the mechanical brakes are used less. An EV brakes much of the time on the electric motor, which then works as a generator and recharges the battery. The brake pads and discs only come into action when you brake harder. The ANWB writes that the brakes of an electric car wear less quickly as a result, but that the mechanical brakes can suffer from rust.

You notice the result in the morning: a grinding or rattling noise during the first few stops, which lasts longer than on a petrol car. The advice from Tesla and from the ADAC, the German motoring organisation, is therefore the same: brake firmly on purpose now and then, so the pads clean and dry the discs again. Have the brakes checked for rust and seized calipers at every service. You can read more about wear and maintenance in brakes on an electric car. Our mechanics are GMTO-certified for hybrid and electric cars (the Dutch qualification for working on high-voltage systems).

We look for the cause first and then replace only what is worn. A squeal is no reason to fit new brakes straight away. This is how a brake check works with us:

1. Listen and test drive: we want to hear the noise ourselves. Does it squeal without braking, only with light braking or at every stop? Cold or warm? That points us in the right direction.
2. Wheels off and measure: we measure the thickness of the brake pads and the brake discs. Manufacturers such as Brembo say brake pads with less than 3 mm of lining are due for replacement. New, they are about 10 to 12 mm. The minimum thickness of the disc is marked on the disc itself (MIN TH) and we measure it at several points.
3. Assess the disc: grooves, a rust lip, blue spots from overheating or a pitted surface. A disc that is too thin, warped or pitted, we replace. We do not skim brake discs.
4. Caliper and slide pins: we check whether the piston and the slide pins move freely and whether the dust boots are intact. Dry or seized slide pins are an often missed cause of squealing.
5. Fitting: are the spring clips and anti-squeal shims in place? When we replace pads, we fit new shims and grease the contact points, as Brembo and Ferodo prescribe.
6. Testing: after the work we test the brakes on the brake tester and take a short test drive.

If the cause is wear, we replace the brake pads per axle, left and right at the same time. If the discs are still thick enough, not warped and not pitted, they stay on. We tell you one price in advance based on your registration number (kenteken), and you can see the old parts. When pads and discs are due for replacement is explained in brake pads and discs: when to replace them. Everything about how we work is on brake replacement in Rotterdam.

New brakes can squeal for the first few hundred kilometres, because the pad and the disc have not fully worn into each other yet. The ANWB advises braking gently for the first 100 kilometres. Manufacturers allow longer: Ferodo 200 kilometres, Brembo about 300 kilometres. During that period you brake gently and gradually and avoid hard emergency stops. Brembo warns that very hard braking in this phase can overheat the friction material, after which the pads keep squealing or vibrating.

If new brakes still squeal after bedding in, something else is going on: a forgotten or reused anti-squeal shim, dry slide pins or a disc that does not sit flat on the hub. Have the fitting checked. How to bed in new brakes properly is explained in bedding in new brakes.

No. Usually not. The ANWB writes that squealing brakes are often harmless, but that the noise can point to a problem that needs attention. A light squeal after rain or after standing still disappears by itself. A squeal that persists is often the wear indicator, and then the pads are due for replacement soon. If you hear grinding of metal on metal, do not drive on.

That is almost without exception the wear indicator. The small metal tab on the brake pad touches the turning disc and squeals. As soon as you brake, the pad presses fully against the disc and the noise stops. Have the brake pads measured and replaced soon, before the lining is completely gone and the disc gets damaged.

At low speed and with light pedal pressure the brake pad vibrates most easily against the disc. The ANWB names cheap or hard brake pads as a cause of squealing in those situations in particular. Dry slide pins and missing anti-squeal shims give the same picture. The car still brakes normally, but the noise is annoying. We look at the fitting and the quality of the pads and tell you in advance what the solution costs.

Yes. Sometimes. According to the ANWB, a squeal caused by rust or dirt after rain or standing still often disappears after a few firm stops on a quiet road. If the noise stays, more is needed: the pads out of the caliper, the slide pins and contact points cleaned and greased, or worn parts replaced. That is work for the workshop, because it involves brake grease and torque settings, and the brakes have to be tested afterwards.

Yes. At first it is. New pads and discs have to wear into each other. The ANWB writes that the squealing usually disappears after a few hundred kilometres. Brake gently during that period: the ANWB says 100 kilometres, Ferodo and Brembo 200 to 300 kilometres. If it still squeals after that, have the fitting checked.

No. Not for the squealing itself. The inspector tests the braking force on the brake tester and looks at the discs, pipes, hoses and the brake fluid level. However, according to the RDW APK manual, no grinding noise of metal on metal may be audible when the wheel is turned. If the pads are nearly worn out, the inspector may note an advisory. If they are completely worn out, it is a fail.

That depends on what we measure. If the cause is the wear indicator and the discs are still thick enough, not warped and not pitted, we replace only the brake pads. If grooves have been cut into the disc because the car was driven on with worn pads, we replace discs and pads together per axle. We tell you in advance what it will be.

• ANWB: Help, mijn auto heeft piepende remmen! (squealing brakes, in Dutch)
• ANWB: Remblokken: wear, bedding in and replacing per axle (in Dutch)
• Brembo: Noises and vibrations: shims, anti-squeal grease and fitting
• Ferodo: Brake Noise: causes of squealing and lubrication of slide pins
• Brembo: How can I tell if my brake pads are worn? (3 mm, wear sensor)
• RDW: APK manual passenger cars: parts and operation of the braking system, article 5.2.31 (in Dutch)