Identifying Your Disc Brake Components
By Courtney Evans
This is how it went down. “Sir, everything went fine with your free tire balancing and rotation, but we checked your brakes and the brake pads and rotors need to be replaced”, said the service manager. Little did he know that I was already aware that it was time for brake maintenance. I replied, “Really? OK, thank you. I’ll handle it”. He handed me my keys and I was on my way. Being able to say that felt really good.
Can you service your brakes? Of course you can. Dollar for dollar, performing your own brake service is one biggest money savers for the DIY mechanic. Your brakes aren’t really that complicated and brake parts aren’t terribly expensive. Its the labor at the mechanic’s shop that gets you.
Previously for me, I was a little bit intimidated by the prospect of a doing-it-myself brake job. I assumed that the process was difficult. I’d read about having to remove the caliper, squeezing the piston with a clamp, using a hammer to loosen seized parts, etc. I thought I’d get stuck somewhere in the process and would have to call for help. But when I performed more research and watched some videos on the internet, I realized that the task was quite easy. Its certainly a dirty job, but whose afraid of a little dirt? Getting dirty is fun!
Let’s take the mystery out of performing your own brake job. What we’ll do in this article is identify the different components that make up your brake system. By identifying the parts, you’ll get comfortable with the system and you’ll be ready for next week’s issue where I’ll show you how to actually get the job done.
Brake System Overview
Essentially, your brake system is a hydraulic system that puts brake fluid under pressure. When you press the brake pedal, a pushrod in the master cylinder squeezes the master cylinder piston. The movement of the piston creates pressure in the brake fluid. This pressure transmits or moves throughout the system and pushes the brake caliper pistons against the brake pads. The brake pads then in turn, create friction on the brake rotors of each wheel, causing the spinning rotor to slow, thereby slowing the vehicle. When you release the brake pedal, the pressure is reduced, returning all of the moving parts back to their previous positions.
The master cylinder creates the pressure needed move the brake caliper pistons. It is composed of a pushrod that is directly connected to the brake pedal. The pushrod “pushes” a piston that compresses a spring. Since the system is closed and the brake fluid cannot escape, the movement of the piston creates the needed pressure in the system.
In most vehicles, the master cylinder it is connected to a brake pressure booster. This brake booster amplifies the movement and pressure that is transmitted from the brake pedal. This device is used to allow the driver to apply less pressure to the brake pedal to stop the vehicle.
Brake Fluid Reservoir
The master cylinder has a brake fluid reservoir that holds the excess brake fluid. This is where you check the brake fluid level. Note that the reservoir has a fill limit mark on it. Don’t ever overfill the reservoir because the fluid level rises and falls during the normal operation of your brakes. On the other hand, don’t under-fill the reservoir either because air can get in the system which will reduce the system pressure, causing a “spongy” brake pedal feel and ineffective brakes.
The brake lines are connected directly to the master cylinder and they carry the fluid to each wheel’s brake caliper. The brake lines are made of metal and are therefore rigid all the way to each wheel well. From there they are extended by rubber brake lines that attach to the caliper. Flexible rubber brake lines have to be used because of the movement of the wheel that it is attached to . Obviously the wheels move up and down, inward and outward, and the front wheels turn. If the lines where rigid at the wheels, they would break as a result of all this movement.
Because rubber brake lines can expand while under pressure, they can be upgraded to braided steel versions that maintain better fluid pressure for a more solid pedal feel and for more effective stopping power. This is one of the upgrades I performed on one of my vehicles. High performance vehicles may come from the factory with steel brake lines.
The brake calipers are used to perform the actual “squeezing” of the brake rotors. The caliper basically looks like a claw. The calipers have a piston, though some vehicles have multi-piston calipers, that push the brake pads onto the brake rotor, causing the friction used to stop the vehicle.
Caliper Guide Pins
The caliper guide pins allow the caliper to slide left and right as the piston pushes the brake pads. They are used on sliding calipers. All vehicles may not have this type of caliper.
Brake pads are used to create the friction on the brake rotors. They are composed of a steel back plate and a friction material. There’s different types of brake pad friction materials in the marketplace. The difference is how the vehicle is to be used, whether performance, racing , or normal driving. Some materials are soft and short-lived while other pads are made of much harder materials and therefore, longer lasting.
Anti-rattle clips are used in some applications to hold the outer brake pad in place and promote even brake pad wear. They are also used to eliminate noise-causing vibrations in the outer pad.
Brake rotors are metal discs, as in the term “Disc Brakes”, that are attached to each wheel hub. The discs spin as your wheels spin. They are “squeezed” by the calipers and pads to stop the vehicle. Brake rotors are very smooth on both sides where they come in contact with the brake pads. If they are not smooth and have deep ridges caused by worn brake pads, the surface can be shaved or “turned” to re-created the smooth surface. Brake rotors have to have a certain thickness in order to be considered turn-able and safe. If the rotor doesn’t meet the thickness guidelines, it has to be replaced.
Rotors can be drilled and/or slotted for high performance applications. Drilled rotors have holes drilled in them to allow faster cooling and gas ventilation during high-heat usage. Slotted rotors have “slots” cut into them to allow better brake pad grip. I used drilled and slotted rotors on my brake upgrade.
Rotor Hold Down Bolt
Small bolt(s) used to attached the brake rotor to the wheel hub.
Brake Sensor Wires
Brake sensor wires are used as a brake pad wear indicator. They are attached to the pads of one of the front wheels and one of the back wheels. They are used on most modern and high-end vehicles. They should be replaced when replacing brake pads. Vehicles without brake sensor wires use a metal clip that rubs against the brake rotor causing a “squeal” that tells you its time for a brake pad change.
Brake fluid is the hydraulic fluid that is used to transmit pressure to the brake caliper and pads. It comes in different “flavors” that is determined by the boiling point. Dot 3 type has a minimum boiling point of 400 degrees Fahrenheit, Dot 4 at 450 degrees, and Dot 5 at 500 degrees. Your vehicle will use Dot 3 or Dot 4.
Brake Bleed Screw
The brake bleed screw is used at each caliper to allow you to remove air from the brake lines. By opening a bleed screw, you evacuate brake fluid at the wheel which removes air bubbles from the system.
That’s it! A quick breakdown of your brake system components and how they work together. There may be minor differences between different types of vehicles, but as a whole, they all work the same.
That wasn’t so daunting, was it? Now that you know the difference between a brake rotor and a brake caliper, you can talk intelligently to that service manager. You’ll know if he/she is trying to pull a fast one and you’ll let’em know that you were born at night, just not last night.