How to Guides

How Brake Pads and Rotors Work

Zaki Moulvi posted this on Jun 4, 2014

The brake system in your car has been changed and improved upon for over a 100 years to finally bring us to the modern disc brake pads and rotor system you see now.  This is by far the most efficient way to stop any fast moving vehicle and can be found being used on planes, trains and automobiles.  Water has little effect on their capability and they seem to wear longer than any other system. 

The Brake System

There is a lot involved in bringing your vehicle to a stop before you even get to the disc brake pads and rotors.  Hydraulic brake fluid is used to initiate the process once you step on the brake pedal.  Fluid is used because like steel, it won’t compress.  Unlike steel it can work its way through twists and turns.  The brake fluid is held inside of the master cylinder and when you step on the brake, a plunger pushes it into the brake lines.  From there it will make its way through a series of brake lines until it reaches the disc brake pad and drum assembly.

The Brake Assembly

There are four major components that make up the brake assembly on your car.  Each one has a significant role in bringing your vehicle to a halt.

  • Caliper:  The caliper works like a vice.  Sitting on top of the brake rotor it is forced closed when you apply pressure to the brake pedal, allowing it to squeeze down onto the rotor.
  • Piston:  An important element to the caliper, the piston reacts to the pressure created by the hydraulic brake fluid by pushing forward and forcing the caliper to close.
  • Brake Pads:  Each caliper contains two disc brake pads, one on either side.  The metal section is commonly referred to as the shoe, and the lining is bonded or riveted to it.  Most brake pad material is a composite of different metal shavings, including steel and copper, that will wear down after extended use.
  • Disc Rotor:  Typically constructed from iron, the disc rotor is a smooth, round disc that is rotating along with the vehicles tires. 

How They Work

Despite all of the other parts involved, when it comes down to it is the disc brake pads and rotor that allow for your vehicle to slow down and then stop.  As the caliper presses down, the disc brake pad is able to make physical contact with the spinning rotor.  The friction that is created by the two elements is enough to bring it to a stop.  

Common Problems

All of this heat and friction created while stopping your car takes it toll on the brake pads.  Arguably the most often changed part on any vehicle, disc brake pads will wear down over time, necessitating that they be changed.  Luckily they are equipped with a metal wear indicator that only protrudes onto the surface of the disc brake rotor once the meat of the pad has eroded away.  When that metal piece makes contact with the rotor it will create an undeniable screech, alerting you to change the disc brake pads.

For optimal braking power, it is important that the metal rotor remain smooth.  This too will develop scratches and grooves over time, especially with prolonged exposure to the wear indicator on the disc brake pad.  The rotor may be machined one or two times to make it smooth again, but after that the metal will become too thin to withstand the heat that is generated when you apply the brakes.  At this point, it will be necessary to change the rotor as well.

 Brake Pad Material

The original disc brake pads were constructed of asbestos, which proved to be dangerous to the environment.  Since then, we have been introduced to other materials that have been proven effective in braking capability.

  • Semi metallic brake pads are the most commonly used today.  They are made up of a composite of metals including steel and copper.  Although durable, they do take their toll on the brake rotors faster than others and react poorly to colder temperatures.
  • Organic brake pads are made using a combination of rubber, glass and fibers.  These are softer than metallic pads and making them quieter, but they do not last as long as other disc brake pad materials and create a lot of dust.
  • Low metallic organic brake pads combine the two by adding a small amount of metal shavings to the organic material to increase its durability.  The added metal makes them noisy and create a lot of brake dust, but they do provide better braking capability then organic pads alone.
  • Ceramic brake pads are the choice for race car drivers.  Although more expensive than other brake pad material, ceramic pads are cleaner, quieter, and lighter than all other materials. 

Your driving habits and priorities will help you choose the type of brake pad you think is best for your vehicle. 

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