There are four kinds of automotive braking systems. Of these, drum brakes and disc brakes are the most common, followed by air brakes and then vacuum brakes. A newer type of braking system, regenerative brakes, may or may not be counted as brakes by your auto technician, but this type of brake is usually reserved for fully electric luxury vehicles. It is important to know the differences between these brake types and why you should know what kind of brakes your own vehicle has.
Just as the name implies, these brakes have a rotating disc that applies pressure to the wheel to make a wheel stop. The disc uses the created friction of the spinning wheel against the non-spinning brake disc to stop the vehicle. If you were to remove your front tires, you would see either two metal or two porcelain discs on either the axle rod or just behind the tires themselves. These are the disc brakes, and they are always your front brakes.
Drum brakes are your heavier brakes installed behind your rear tires. Trucks and cars with all-wheel drive will have them, as will some older, longer, and heavier vehicles. Drum brakes provide extra stopping power for these vehicles that would not ordinarily stop with just the disc brakes on the front tires of the vehicle. If you drive a lighter passenger vehicle or a vehicle without four-wheel drive, you may not have a set of drum brakes on your vehicle.
Unless you drive a semi or a construction vehicle, air brakes are not your problem. These brakes are rarely, if ever, installed on passenger vehicles. Air brakes provide extra compressed air to slow, stop, and prevent multiple axles and multiple wheels from continuing to roll forward.
Vacuum brakes are similar to air brakes in that they are for much heavier vehicles. In most cases, vacuum brakes are meant for trains only, but they have been used by semi and heavy duty commercial trucks. Rather than compressing air to stop a vehicle, they suck air out of the brake lines to apply vacuum pressure to the wheels.
Importance of Knowing What Brakes You Have
It is important to know what brakes you have so that there are no surprises when your technician tells you that you need to replace four brakes instead of two. It also helps you with understanding how your vehicle handles and why. Repairs on drum and disc brakes are very different too. You would not perform certain brake repairs on drum brakes that are meant for disc brakes and vice versa. Likewise, repairs on air or vacuum brakes are nothing like repairs on disc or drum brakes.