Aside from oil changes and regular maintenance, brake noises are without a doubt, the most common complaints automotive technicians have to deal with on a daily basis. And for a good reason. The brake system is arguably the hardest working system on your vehicle. It has to bring your car to a halt no matter the weather and the speed you are traveling at. It is also constantly exposed to water, snow, dirt, mud, and sand as well as sudden rises and drops in temperature. It’s not that hard to understand why it may sometimes cry for help and start making weird sounds. Brakes are not complicated systems so identifying the different noises they make, where they come from and fixing them is usually quite easy.
Table of Contents
- How the braking system works
- But why are my brakes so noisy then?
- Different brake noise and their fixes
How the braking system works
To understand why brake can suddenly become noisy, you first need to understand how the brake system works and what components are moving when the brakes are applied.
When you step on the brake pedal, a lever pushes a piston into a narrow cylinder filled with hydraulic fluid. This sends the pressurized fluid to the brakes of the car. Brake fluid can’t be compressed so the pressure will be equally applied to all four brakes.
Disc brake systems
The brake fluid will push on the pistons located inside the calipers, which will, in turn, apply pressure to the brake pads. The pads will rub against the brake rotors to slow down and stop the wheels. It is this friction of the pads against the rotor that will cause the brake pads to gradually wear out.
Drum brake systems
The brake fluid will push two small pistons inside the brake cylinder, which will push the brake shoes against the drum in order to slow down and stop the wheel. The rubbing of the shoes will eventually wear them out and they will need to be replaced.
It’s worth mentioning that, brake systems on conventional vehicle work in a 70/30 power distribution, meaning that 70% of the brake power will be sent to the front axle of the vehicle while the rest is taken care of by the rear axle. Brake systems are made that way to send most of the weight of the car towards the front when braking. A setup like this also explains why drum brakes are almost exclusively used on rear axles. At least, this is true for all vehicles made after the 70’s. Disc brakes will consequently need to be replaced almost twice as often as drum brakes and will also be more prone to strange noises problem.
But why are my brakes so noisy then?
Vibration is the main cause of brake noises and all brake components vibrate to a certain degree and generate an initial noise. Most of the time, this initial noise can’t be perceived by the human ear partly due to the attenuation effect generated in the system by the larger components of the brake. The key to initial noise attenuation is the stability or rigidity of the brake components. On most OEM brake parts, attenuation is also supported by insulating shims or noise canceling gaskets that reduce as much vibration between the contact surface of the rotors and the brake pada as possible.
More important vibrations can also be caused by rust, deformed or loose parts, uneven wear or sometimes completely worn out components needing to be replaced. As components become brittle or wear out due to heat and stress, they can become loose and any vibration resulting from the different points in contact will cause an audible and annoying noise such as a whistle or a metal grinding noise.
Many technicians believe that replacing pads with ones made of a “softer” friction material, typically “ceramic” brake pads, will solve noise problems. In fact, and even if it is sometimes true, changing to a “softer” material will actually modify the balance of the brakes and will cause the noise frequency to reach an inaudible noise level. However, the owner will have to make an important concession: softer pads wear out faster and their service life is usually a lot shorter than regular pads.
Different brake noise and their fixes
Whistling noise while the brake pedal is depressed
If your car is often parked at the same place for a day or two, a slight whistling noise may be heard the first couple of times you press on the brake and it is nothing to worry about. Rain and water can leave a thin layer of rust on the rotors after the car is left sitting there for a while. All the rust will be cleaned off after the pads have rubbed against the rotors a bit. A whistling noise can also sometimes be heard during light braking and while the brakes are still cold. Depress and gently hold the brake pedal to heat up the brake pads and the whistling should go away.
If the noise is still present after a couple of blocks, ask yourself when was the last time you had your brake system serviced. As the pads wear out, dust will start to build upon the various components and excessive dust on the pad surfaces, for example, may cause a whistling noise. Drum brakes are particularly affected by the dust coming from the brake shoes. Unlike disc brake systems, dust simply can’t escape the drums or be washed by water when driving in the rain. Removing the calipers and/or drum and spraying everything with brake cleaner could do the trick. If for some reason it doesn’t, your whole brake system will probably need to be serviced.
Beyond all these factors, some pads use shims as insulators that can move or rust after a while causing a shim resonance problem, a high-frequency vibration that is a prerequisite for brake whistling. To remedy this problem, an application of copper grease on the back of the shim plates is recommended. The grease will camouflage the resonance by preventing the shims to touch and vibrate against the back of the brake pads. An even more extreme and permanent solution is to apply a thin layer of windshield urethane to form a permanent cushion between the shims, the pads and the calipers to dampen noisy vibrations.
Angle of attack
Whistling may also be related to a wrong angle of attack at the contact point between the pads and the rotor. To overcome this problem, you can file the edges of all the pads. However, it should be noted that it is strongly discouraged to deburr the pads when you install a new set of rotors. It’s better to let the pads and the rotors break-in and settle for a while and perform any corrections later if the whistling is still present.
The vitrification of the brake pads is also a possible hypothesis. Whenever your brakes are solicited for a long city drive or after an emergency stop, the rotors could become so hot that they will literally cook the surface of the pads, causing the friction surfaces to glaze (a slight hardening or peeling is formed on the surface of the pads/shoes) making them slip on the rotors and ultimately whistle when in use.
In very difficult conditions like repeated braking in heavy traffic conditions or driving down hilly roads, the temperature of the rotors can reach over 1,000 degrees. When working at such high heat level, whistling brakes is a common phenomenon due to a change in the metallurgical structure at the surface of the drum or disc and is not that much a concern other than being annoying. Make sure to get your brakes inspected after such a drive to make sure your pads aren’t vitrified. Driving with slippery pads is riskier since the braking distance can be 1/3 longer than usual and quickly turn a near save into a car crash.
A whistling brake system can also be a warning sign to the owner. Most modern brake pads have wear indicators, i.e. a small metal protrusion attached to the metal plate of the brake pad which will come into contact with the rotor when the thickness of the pads becomes thin enough, producing a high-pitched whistling sound. The noise here is happening on-purpose and serves as a reminder that your brake pads need to be replaced soon. There’s no need to panic yet as engineers set the wear indicators to start whistling when there’s around 2mm of brake pad thickness left. Don’t wait until it’s all gone though, as doing so will also damage other essential and expensive brake components making your routine brake change a lot more pricey than it should normally be.
Whistling noise when the brake pedal is released
When you press the brakes, it’s expected and absolutely normal to hear some noise during deceleration. The brakes linkage can crack, the brake booster can blow, the tires can make some grunting when the brake pedal is pressed hard. What is even more disconcerting is when the brakes start to whistle and you don’t even have the foot on the pedal yet.
The main reason for brake noises heard when the brake system is not actually in use is that something is seized or not moving freely, preventing the pads to return to their original position when the brake pedal is released. The most common causes would be a seized caliper piston, brake pads seized in their respective holders, or stuck guide pins.
This condition can happen if the vehicle is not used often enough but it will also happen naturally on most vehicle and that is why it’s recommended by most car manufacturers to have your brake system serviced once a year. The seizure of most parts mentioned earlier will typically wear down brake pads in under a month or two depending on how bad is the seizure.
It’s worth mentioning that driving a car with a jammed caliper or seized guide pins, even slightly, will greatly reduce your vehicle’s fuel efficiency, making the overall cost of your brake replacement a lot more expensive in the end.
We highly recommend you use high-temperature silicone grease on the caliper slides and floating bushings when servicing your brakes to prevent the calipers from bending and grazing. Replace all anti-rattle fasteners, shims, springs and anti-dust boots at the first sign of damage. Make sure the guide pins can move freely, as this may prevent the brake caliper from engaging properly which could also produce noises.
The parking brake or emergency brake can also come into trouble with time and cause a constant whistling noise while driving. The problem usually lies under the car where the parking brake cables and link are located. Since the cables are attached directly under the car and with nothing to protect them from whatever mother nature throws at them, they can start to rust and they won’t be able to move as freely as they should. What will happen is that the rust will prevent the cables to automatically return to the OFF position when the handbrake is released, causing the read brake pads to slightly stay in contact with the rotors/drums creating a distinct whistling sound. The annoying noise sometimes stops after a block or two but be sure that it will be back again the next time your release the parking brake lever.
The correct way to fix this is to unhook the cable from the brake pads/shoes and to pull the handbrake and watch which cable is not moving as it should. The faulty parking brake cable will then have to be replaced. To prevent any premature handbrake cable seizure, spray some anti-rust lubricant inside the cables and at each opening to block out sand and water from entering.
It’s not perfect but it will definitely help!
Squeaking sounds are probably the hardest problems to troubleshoot. They usually require the help of another person to locate the sound while pressing and depressing the brake pedal and they can easily be mistaken for a suspension noise problem.
In most cases, squeaking coming from the braking system are heard when the vehicle is stopped and the brakes are depressed, usually coming from the rear. The reason why it’s usually a rear axle problem is that drum brakes tend to squeak more when they are not correctly lubricated.
The quick fix would be to remove the drums, clean everything with brake cleaner and spray a thick layer of lubricant behind the brakes shoes where they touch the backing plates. In the best of worlds, a complete disassembly of all the springs and whatnot would be required to carefully remove all the rust on the brake shoes’ contact points, lubricate and re-assemble everything. But if all you want is to get rid of the noise, spraying grease should do just fine.
Whenever you press the brake pedal and you hear not a slight and annoying whistle, but a grinding sound that makes you cringe and attracts the attention of everyone around you, it probably means that your brake pads are way past the wear indicator and the backing plates are now directly in contact with the rotors.
This is a serious security issue and driving your car is definitely not recommended. When the brake pads are that thin, they could literally slip out of the brake pad retainers and fall out of your vehicle.
In the best case scenario, the caliper pistons would then enter in direct contact with the rotors while braking. Pistons won’t be braking as well as brake pads but you should still be able to somewhat stop the car. Both calipers will need to be replaced but it’s still not that bad. In the worst case scenario, the caliper pistons would pop out, releasing all the brake fluid on the floor, rendering the brake pedal useless. The brakes wouldn’t respond anymore and you would have to rely on the emergency brake to stop the vehicle.
On the other hand, a grinding noise can sometimes be perceptible without the pads being worn at all. Another instance of such noise happens when the surface of the rotors is heavily scratched, wavy or contaminated by rust. The first thing to try would be to sand the rotors with a 120 to 150-grit sandpaper until the surface is even. If there’s a good amount of rust on the surface in contact with the brake pads, nothing will be able to save them and they will need to be replaced.
A repetitive low-pitched thud when the brake pedal is depressed, often accompanied by vibrations felt in your foot usually means that the rotors or drums overheated and that their runouts should be checked. When the runout of a rotor/drum is out of specs, it will start to wobble which will cause jerky braking and vibrations in the brake pedal.
A good rule of thumb to find out if the problem comes from the front or the rear axle is to check if the steering wheel is shaking while braking from 70km/h. If it is, the problem comes from the front wheels and the rotors need to be replaced. If it’s not, try pulling the handbrake while driving 10-15 km/h. If the rear drums are faulty, you should feel the car starting to jerk and you should feel the vibration in your hand holding the handbrake lever.
The replacement of the faulty components should be performed as soon as possible since vibrations happening at high speed can quickly damage numerous suspension and steering components like ball joints and tie rod ends.
As time passes, the brake pads and backing shims will gradually rust and wear out and could create rattles when driving over potholes. This is especially true for car owners who don’t drive more than 5000 km a year and still have their brake system serviced regularly.
Every time the auto mechanic performs a brake service, he will remove the rust from the brake pads and backing shims, grinding a little more metal each time. Under normal conditions, brake pads are replaced every 2-3 brake service but if you don’t drive that much and keep the same brake pads for 10 years, the amount of shaved metal could eventually make the pads become loose. Backing shims usually rust out after 2-3 years and their vibration dampening efficiency drops near zero anyway. On some occasions, not driving a car can be even worse than driving it every day, especially when it comes to rust.
If this is your case, there’s not really anything else to do other than to replace the pads even if they still look thick enough.
Repetitive friction noise
If you can hear a constant and repetitive shh-shh-shh kind of noise coming from one of your wheels, there are 3 possible explanations. The first one would be that there is something like a small rock, a leaf or any other small foreign object lodged between the rotor and another component of the braking system. It could also be caused by the ridge of rust on the edge of a rotor coming into contact with the pad holder as it turns. And finally, the most common occurrence is that one of the pads or one of the guide pins is just beginning to seize, preventing one of the pads from retracting far enough to stay clear of the rotor.
No matter which explanation is the right one, your brake system will need to be disassembled and serviced by a knowledgeable mechanic.
Any noise is the result of vibration. The sound depends on the frequency of the vibration, meaning that a slow vibration will produce some kind of “grunt” while a quick vibration will produce some kind of “hissing”. Whenever inspecting a car to find the source of a specific brake noise, always keep in mind that a vibrating component can cause a secondary vibration in another part. Try to see in your head what parts are moving and use your ears to locate the problem. Troubleshooting car noises is not always easy but it will become easier as you gain experience. Give it some efforts and practice a lot and you should be able to identify and fix most brake-related noises in no time!