Braking Fundamentals: Brake Pads, Rotors and Fluid


Wearever gold brake pads

You know something’s wrong with your brakes. Maybe it’s a grinding or scraping noise, pulling to one side when you slow down, or even a spongy brake pedal. The first step in diagnosing the source of the problem is understanding the main parts of a brake system and how they work together.

Brake pads and shims

When you push on the pedal for your car brakes, calipers clamp the brake pads onto the rotors to reduce speed and then stop the vehicle. Brake pads get the glory as the main component in stopping, but equally important are the rotors. Helping to reduce noise and vibration are the brake pad shims. Shims are made of metal or rubber and found on the back of brake pads, in between the pads and the calipers. In addition to reducing noise and vibration, shims manufactured from titanium also protect calipers and fluids from damage caused by excessive heat.

Troubleshooting brake pads

To do their job effectively, the pads must be able to absorb enough energy and heat. When there is too much wear or heat, brake pad efficiency is reduced, along with your stopping power. Car brake pad indicators are designed to emit a scraping sound when the pads are worn out. If you hear this or a grinding sound when you apply your brakes, the pads need replacing. Brake pads should be replaced in pairs.

Learn how to choose the right brake pads for your vehicle and how to replace brake pads yourself.

Brake rotors

Car brakesWhen you press the brake pedal, the calipers cause the brake pads to clamp down on the rotors (also called brake discs). When pressure is applied to the brake rotors, it prevents the wheel from spinning, which means that your brake rotors are as important as the pads when it comes to safety.

Most rotors are made from cast iron—more specifically, gray iron—because it disperses heat well, which is important to avoid overheating and brake fade. High performance vehicles use ceramic rotors, which are lighter and more stable at high speeds and all temperatures. They are, however, more expensive. Some rotors also come ‘painted‘ with a special, rust-inhibiting coating. This ensures that the rotors look good and last longer.

Troubleshooting brake rotors

Rotors will need to be replaced by 70,000 miles on most vehicles, but it depends on use. Rotors, like brake pads, should be replaced in pairs for even stopping performance. Your rotors may need to be replaced if you see or hear any of these signs:

  • Grooves worn into the rotor by the brake pads
  • Squealing, squeaking, or grinding sounds when braking
  • Vibration or wobbling when braking.

Learn how to choose rotors and how to replace rotors yourself.

Brake fluid

brake fluid designation sign

Source | Brian Snelson/Flickr

Brake fluid is “incompressible,” so that when the brake pedal is pushed, the fluid forces brake parts to work together to slow the wheel. Brake fluid also lubricates parts in the braking system. In the United States, there are four designations of brake fluid: DOT 3, DOT 4, DOT 5, and DOT 5.1. Each contains a mixture of chemicals with specified dry and wet boiling points. When your brake fluid has just been replaced, this is called the “dry” boiling point temperature. As water finds its way into the system, the “wet” boiling temperature is the benchmark you should use. To choose the best brake fluid for your vehicle, consult your owner’s manual.

Troubleshooting brake fluids

Because brake fluid is also hygroscopic (attracts water) it starts degrading the moment the bottle is opened, so it should be replaced every two years. A sure sign that your brake fluid is degrading is a ‘spongy’ brake pedal, or a pedal that continually creeps toward the floor. When this happens, it’s time to look at replacing your brake fluid, or bleeding air from the brake fluid lines.

Learn more about how to change brake fluids and how to bleed brake fluids.

For information about the brake parts offered by Advance Auto Parts, check out our buying guide. Are you diagnosing your own brake needs? Tell us about your brake project in the comments.


  1. What cause breaks to shimmery when applying pressure on pedal

  2. What is the tool used to remove the rear rotors of a 2011 dodge avenger

  3. I’m one for semantics, and I think the explanations above are good, but may not be all-inclusive. Here’s my amendments:

    Drilled: Most often called “Dimpled” in my experience, and also less confusing to call it that (see below). This is when the holes through the rotor do not go all the way through to the other side. Doesn’t weaken the rotor as much this way.

    Cross-Drilled: Often just shortened to “Drilled” (hence the confusion). Has holes drilled all the way through the entire rotor. Slightly more efficient at heat removal than Dimpled, but weakens the structure of the rotors more.

    Slotted: Little canals gouged partially into the rotor surface. Works great by itself, or when combined with Dimpled or Cross-Drilled technologies.

    Vented: Basically describes a rotor that is not a solid piece of metal, but is essentially a hollow sandwich of metal slabs, with channels in bewtween to facilitate airflow through the interior of the rotor, and help dissipate heat more quickly.

    Solid: Or “Non-Vented”. No sandwich; no air channels. Just a chunk of metal. Most modern cars do not use this type of rotor, as it is more efficent for them to be vented.

  4. Dennis Kitchings says:

    One of two things. You may have a wheel that is out of balance especially if you have had a flat and had it plugged or put something like fix a flat in it (which you should not do). If moving rotating the tires to the rear does not help, then the rotors are warped. Besides normal wear and heating, rotors will warp if you have aluminum/alloy wheels and the lugs are tightened too tight. Most tire places us an impact wrench to change tires with, and an inexperienced person can tighten the lugs too much very quickly. Sometimes having the rotors resurfaced can fix this, but I recommend new rotors and having this done at a reputable tire place or yourself if you are the mechanical type as I am.

  5. Brake Pads says:

    Nice informative blog for Brake Pads, Rotors and Fluid.

  6. I agree that it is a good idea to tap your brakes instead of braking continually. It makes sense that doing this can help your make the most out of the braking system. I can see how choosing a reputable car shop can help you get the best services and quality parts to help you avoid accidents.

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