Car Brakes Explained

While they might generate fewer column inches than engines, gearboxes or infotainment systems, the brakes are arguably the most important part of your car. Those little pads do a mighty important job in slowing down and stopping several tonnes of metal hurtling along at motorway speeds, keeping you and other roads users safe. It's a legal requirement to keep your brakes in good working order, and it could save your life. Read our handy guide to understand how brakes work and what you need to stay on top of.

Car brakes explained

Parts of a braking system

Modern braking systems feature many components working together to slow down your vehicle and bring it to a controlled stop. The brake pedal that you press with your foot is connected to the master cylinder in the engine compartment. This cylinder is filled with brake fluid, and the hydraulic pressure created when you depress the pedal travels along a series of pipes to activate pistons in the hub assembly of each wheel. These pistons force the brake pads onto rotating parts connected to the wheel, and the friction slows the car.

Disc brakes

Disc brakes are the most commonly found type of car brakes. The disc braking system consists of a brake disc, a brake calliper and brake pads. The pads press against a rotating brake disc to apply friction and slow the revolution of the wheel.

Drum brakes

Before disc brakes took over, drum brakes were the most common type of brakes found in cars. Instead of brake pads pinching a disc, curved brake shoes press against the inside of a rotating drum to apply the friction. Many modern cars are fitted with disc brakes on the harder-working front wheels, and drum brakes on the rear wheels.

Anti-lock brakes

Before the advent of anti-lock brakes (ABS), you had to pump your foot on the brake pedal when slowing down from speed, or risk going into a skid. Modern cars are fitted with ABS, which uses sensors on the wheel hubs to tell how fast each wheel is rotating. The computer-controlled system then uses valves and pumps to reduce and increase the braking pressure several times a second, meaning the wheels don’t lock up, and giving the driver more control. ABS only kicks in when you brake sharply at speed. The ABS system will test itself every time the ignition is turned on. If any fault is detected, it will disable itself, turn on a warning light and the normal braking system will be used.

How long do brake pads last?

Brake pads can last between 30,000 miles and 70,000 miles, or possibly more depending on how heavy your car is and how it’s driven. City driving puts more wear and tear on brake pads than motorway driving.

There are also various brake pad materials with differing levels of durability. Ceramic brake pads tend to last the longest but are more expensive, while organic brake pads are usually the cheapest and least durable. Low metallic brake pads should last longer than organic ones, though they can be noisy. Semi-metallic or sintered brake pads are durable but can wear down brake discs more quickly. The front brake pads work harder than the rear ones so tend to wear out sooner.

How do I know when to change my brake pads?

The first thing to look out for is the warning light on the car’s dashboard. Some cars aren’t equipped with brake pad sensors, so won’t have this – if this applies to your vehicle then regular professional inspections of your brake pads are a must. Loud screeching, the vehicle pulling to one side when braking and vibrations when you depress the pedal can also be signs you need new brake pads. Depending on the type of vehicle, you may be able to inspect the pads visually – there should be at least 3mm of pad visible. Check out this article on how to check brake pads for further information.

How long should brake discs last?

Brake discs wear down more slowly than pads, but depending on factors including how you drive and what type of pads you use, they should be good for anywhere between 80,000 and 120,000 miles. However, replacing both discs and pads at the same time ensures maximum safety.

Other types of brakes

Many modern and hybrid vehicles are fitted with electromagnetic braking systems. This applies a magnetic flux in a direction perpendicular to the wheel’s rotation for frictionless braking, meaning there’s no need to replace brake shoes. Power-assisted brakes, also known as servo-brakes or vacuum-assisted brakes, use a vacuum created via a pipe running to the engine’s air intake (or an engine-driven hydraulic pump in diesels), to reduce the effort you need to apply to the brake pedal. At the other end of the spectrum, the mechanical brakes found in some vintage cars use rods and pivots in place of hydraulics – proper set-up is crucial with these.

Things to look out for

  • Fluid leaks. You should replace the fluid every few years, usually when you get the brakes serviced. If your brake pedal starts responding more slowly, it could be a sign your brake fluid is contaminated with moisture, rust or dust, and needs replacing. A low or fading pedal without visible fluid loss could mean a failing master cylinder is leaking internally.
  • Brake drag and pulling to one side. This could be a sign of a problem with the seal keeping your hydraulic fluid in, or a failed dust boot allowing dirt into the calliper piston. Worn-out brake hoses can also cause pulling to one side.
  • A spongy brake pedal. Air may have got into the brake line connecting the master cylinder to the brake hoses.
  • Shaking or wobbling in the steering wheel when you brake. This can be caused by the disc wearing unevenly, leaving the pad in contact even when the pedal is not being pressed.
  • Grinding sounds. These can indicate damage to pads or discs.

How to prolong the life of your brakes

  • Brake gently. Heavy braking generates extra friction and puts more strain on your brakes.
  • Use the handbrake at the lights. Holding your car on the footbrake wears out the pads quicker.
  • Use engine braking where possible. Riding the brakes downhill increases the wear on brake pads.
  • Avoid rush hour. An added disadvantage of rush hour is that all that braking means you’ll need to get your brakes serviced sooner.
  • Don’t tailgate. This will reduce the need for heavy braking.
  • Remove unneccessary weight. Heavier loads put more stress on the brakes.
  • Clean your brakes. Do this when you clean the rest of your car and reduce the risk of rust.

Your brakes are a vital component of your car and are well worth looking after. Care for them properly and you’ll save money as well as keep yourself safe. Take a look at our guide on maintenance tips for how to keep your car running smoothly.

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