Car Brakes

How brakes work

A typical disc brake system features a few simple moving parts that, when working properly, quickly and effectively slow down car. Let’s start with a typical braking motion when driving. When you push your foot on the brake pedal, it actuates a vacuum booster (also known as the brake booster) that multiplies the amount of force produced by your foot pushing on the pedal. Without the multiplication of force produced by the brake booster, pushing down on the brake pedal would require a high amount of physical effort.

This force is then transferred to the master cylinder, a reservoir filled with brake fluid. The master cylinder is so-called because it typically controls two sets of brakes – the front and the rear – independently using brake lines filled with brake fluid. Although the master cylinder applies brake pressure to the front and rear evenly when you push the brake pedal, the advantage to having two systems is that if one were to fail, a driver could still bring the vehicle to a stop.

When you press the brake pedal, which is multiplied by the booster then transferred to the master cylinder, you are controlling the brakes via the hydraulic action of the brake fluid in the brake line. That is, every time you press the brake pedal it physically moves hydraulic brake fluid to actuate each individual brake.

Disc brake components

A disc brake involves a surprisingly few number of parts to initiate a stopping motion. If you safely jack up your car while changing a tire, when wheel off your vehicle, the first thing you’ll notice is likely the rotor – it’s the “disc” in the disc brake. The rotor is directly attached to the wheel hub itself, so when the wheel spins, the rotor spins.

The next most significant part of the disc brake system is the caliper, which fits snugly over the brake rotor almost like a clamp. Housed within the caliper are the brake pads. The brake pads are the part of the brake most responsible for stopping. When pushed into motion by the brake piston (also within the caliper), these two heavy metal or ceramic plates come in contact with the rotor, using the power of friction to slow down the vehicle.

Because your vehicle’s stopping power depends on two surfaces coming in direct contact to produce friction, both the rotor and the pad need to be clean, level and free of debris to work properly. Although pads are designed to be durable, they do wear down over time.

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Video: What your brakes are trying to tell you

Signs you need brake repairs

Although brake components such as brake pads and brake rotors are designed for durability due to their frequent use, like many car parts, brake components do eventually wear down and necessitate replacement. There are some obvious, and not so obvious, signals that indicate brake repairs are needed.


If you notice a high-pitched squealing sound when you apply the brakes, it’s a good indicator that your brakes need to be replaced or at the very least inspected. This is the most common indicators brake repairs will be needed. Many vehicle and brake component manufacturers engineer wear indicators into their brakes to produce this sound to notify the driver brake work is needed.

Other factors that can produce a high-pitched squealing from the brakes include a build-up of brake dust from the brake pads being worn down, debris or rust on the surface of the rotor or brake pads becoming glazed over from high heat. Due to the multiple possible causes that can produce squealing brakes, including improper installation, missing anti-rattle clips or poor surface contact with the rotor, it’s a good idea to have your brakes inspected when you hear squealing.


The sound of brakes grinding is not only cringe-inducing, it’s a sure sign something’s amiss with your vehicle’s braking system. If you hear grinding sounds when you apply pressure to your brake pedal, it means the pads weren’t replaced in time or something is rubbing against the brake rotors the wrong way.

The brake pads may be beyond their wear limit, they may be coming into rough, uneven contact with the rotors, or it can be something more sinister like brake calipers or pistons grinding against the rotor (they’re not supposed to). Get your brakes inspected and repaired (if necessary) immediately.

Pulsations or vibrations when the brake pedal is applied

Feeling pulsations or vibrations when you apply the brake pedal typically indicates the brake rotor is significantly warn or warped. Effective braking power relies on the brake pads and brake rotor coming into contact cleanly, that is the entire surface brake pad contacting the brake rotor simultaneously.

A rotor that is warped by friction or heat, or worn beyond acceptable limits, can create vibrations or pulsations; it’s a sure indicator you should visit a brake specialist or auto service center as soon as possible. However, pulsations or vibrations should not be confused with a vehicle’s anti-lock braking system, which prevents the brakes from locking when heavy brake pressure is applied, particularly in slippery driving conditions such as rain, snow or ice.

Loss of pressure on the brake pedal

When your foot presses on the brake pedal, you should feel a firm response that becomes increasingly firm as you press down harder. If you own late-model vehicle (and not a classic or vintage vehicle without modern braking technology), a brake pedal that feels mushy or can be pressed all the way down to the floor can indicate several things.

It could be a relatively minor problem such as  a leak or gap in the brake lines allowing air to enter and diminish braking power or the brake pedal may need to be adjusted, or it may be something much more serious, such as a failing brake system. Have the brake system inspected by a professional.

Types of brake repairs

The type of brake repair your vehicle requires will vary depending on the problem, but there are a few routine brake repairs that are a part of regular maintenance and upkeep.

Brake pad replacement

One of the simplest and least costly brake repairs (if no other repair are needed), replacing a vehicle’s brake pads can be accomplished by a DIY mechanic with moderate experience. Replacement brake pads for common non-luxury vehicles frequently cost less than $100 per axle, but be careful, as improper installation of brake pads can cause some of the symptoms noted above.

Rotor resurfacing

It’s usually a good idea to consider resurfacing or “turning” the rotor when it comes time to replace the brake pads. Because your vehicle’s brake stopping power relies on as much surface area between the rotor and brake coming in contact cleanly, a rotor that is scored or worn may need to be resurfaced.

Brake rotors typically include wear indicators that show if there’s enough material left to be resurfaced. A mechanic can also check the thickness of the rotor against the manufacturer’s recommendations. If there’s enough remaining material, a technician will place the rotor on a special lathe and scrape just enough material away to create a new evenly smooth rotor surface. If there’s not enough material, the rotors will need to be replaced.

Other adjustments

Since the braking system relies on multiple interconnected components from the brake pedal to the brake booster to the master cylinder to the brake fluid to the brake lines and each individual caliper, piston, pad and rotor, it’s important to find a trusted, experienced mechanic or technician who can make recommendations and adjustments to the brake system when needed.

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