Many people don’t realize there’s a difference between antilock brakes and power brakes—and the two terms are not interchangeable. Let’s discuss that difference, and offer a bit of car maintenance advice.
If you’ve ever tried to apply the brakes on a car that’s coasting with the engine off, you’ve got an idea of the effort required to stop without power brakes. Power-assisted brakes were first developed in the 1940s for heavy trucks; as cars started getting bigger and heavier, power brakes became more and more commonplace. Today it’s rare to find any car that doesn’t come equipped with power brakes.
The engine naturally produces a great deal of vacuum pressure. The power brakes’ vacuum booster sits behind the master cylinder, the device that actually sends hydraulic pressure through the brake lines to the brakes. The vacuum booster siphons vacuum pressure from the engine by way of a check valve; it uses that vacuum to amplify the physical pressure that the driver applies to the brake pedal. The vacuum booster contains a diaphragm that divides the booster; on one side of the diaphragm is normal atmospheric pressure, while the other side has extremely low pressure from engine vacuum. Press on the brake pedal, and it introduces air into the booster and moves the diaphragm, also moving a shaft that leads to the master cylinder and actuates the brakes. The result? Little effort is required to stop the vehicle.
Now that we have covered the basics of power brakes, let’s talk about the difference between antilock brakes and power brakes.
For years, drivers have experienced loss of control and steering when their wheels lock up under hard braking. However, brakes perform best when they are right on the verge of lockup. Proportioning valves that equalize braking pressure between the front and rear wheels have been a help in the past, but it wasn’t until the advent of antilock brakes that the problem of brake lockup and skidding was truly addressed.
When considering the difference between antilock brakes and power brakes, remember that any antilock system is also going to be power-assisted. With that distinction aside, antilock brakes use speed sensors on each wheel that give feedback to the car’s engine computer. At the threshold of locking up, a wheel will begin to turn slower than the other wheels on the car. That’s when the computer processes the reading from that wheel, then closes a valve to that particular wheel in order to equalize pressure between all wheels and prevent skidding. This all happens very quickly, with the cycle happening as much as 15 times per second. Drivers may sometimes feel a pulsating sensation through the brake pedal—that’s normal, it’s just the ABS doing its job.
Now that we have explained the difference between antilock and power brakes, we’re ready to answer more questions and offer car maintenance advice. Feel free to swing by your local Big O Tires, we’ll be happy to help you out! For more information on brakes and all things automotive, visit our Facebook, Twitter, and YouTube pages.