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How Emergency Brakes Work

At All Tech Automotive, we believe you should thoroughly know every part of your vehicle and how every part works. We found this article on how emergency brakes work to give you a better understanding of your brake system. 

How Emergency Brakes Work

You're 16 years old. Your father has decided it would be a great idea to take you to the steepest hill in town and make you stop precariously at the stop sign that is halfway up the hill. You're driving a stick shift. As you stop, he reaches over and puts on the emergency brake. You notice three cars pulling up behind you. Your father snickers. You break into a cold sweat. But for a second, you feel safe. Because the emergency brake is on. But what exactly is holding you in place?

Emergency brakes are a secondary braking system installed in motor vehicles. Also known as e-brakes, hand brakes and parking brakes, emergency brakes are not powered by hydraulics and are independent of the service brakes used to slow and stop vehicles. There are state and federal laws requiring emergency brakes for motor vehicles [source: NHTSA].

There are four types of emergency brakes:

  • Stick lever, which is generally found under the instrument panel (found in older-model vehicles)
  • Center lever, which is found in between separated front seats
  • Pedal, which is found to the left of the floor pedals
  • Electric or push button, which are found amongst the other console controls

Because most modern braking systems have failsafe measures and warning systems, such as on-dash brake-warning lights and low-fluid sensors, the emergency brake is most often used as a parking brake device. But the e-brake is called an emergency brake for a reason -- using it can save your life.

Emergency Brake Parts

Using only levers and cables, each type of emergency brake is completely mechanical and bypasses the normal brake system. This ensures that a vehicle can be brought to a complete stop if there's a failure of the brake system [source: Ofria].

When you set the emergency brake, the brake cable passes through an intermediate lever, which increases the force of your pull, and then passes through an equalizer. At the U-shaped equalizer, the cable is split in two. The equalizer divides the force and sends it evenly across the two cables connected to the rear wheels [source: Owen].

Motor vehicles use either drum brakes or disc brakes. Drum brakes are common in the rear wheels, while disc brakes are most common on the front wheels (or all four wheels). In a rear drum situation, the emergency brake cable runs directly to the brake shoes, bypassing the hydraulic brake system. In this simple, mechanical bypass, the emergency brake system requires no extra parts to control the brakes [source: Owen].

Cars with rear disc brakes have a more complicated emergency brake system, sometimes requiring an entire drum brake system to be mounted inside of the rear rotor, called an exclusive parking brake or auxiliary drum brake [source: Owen].

When the vehicle has rear disc brakes without an auxiliary drum brake, a caliper-actuated parking brake system is used. With this system, an additional lever and corkscrew is added to the existing caliper piston. When the emergency brake is pulled, the lever forces the corkscrew against caliper piston, and applies the brakes, again bypassing the hydraulic braking system. 

Electric e-brakes are available on some cars today. Instead of having a pedal, stick or center console lever, a small button on the dash signals an electric motor to pull the brake cable. Advanced electric brake systems utilize computer-controlled motors to engage the brake caliper [source: Zangari].

When to Use the Emergency Brake

Using the emergency brake to stop a moving vehicle outside of a total brake failure is not recommended and can damage your brake system. This is why it's not a good idea to pretend you're a racecar driver and slam on the e-brake to spin in a circle. Driving with your emergency brake engaged can also cause damage to the emergency brake cable and the service brakes. If this happens to you, have your brake shoes and rotors checked as soon as possible, to ensure everything is OK.

The most common use of the emergency brake is as a parking brake. Those who drive manual transmission vehicles, or stick shifts, usually engage the emergency brake every time they exit the car. If not engaged, the car might just roll away all on its own. Automatic transmission drivers tend to use the emergency brake far less, if at all.

It's recommended that you engage the emergency brake anytime the vehicle is parked on a hill, whether it's an automatic or standard transmission. For an automatic, setting the emergency brake before you release the service brake pedal will keep weight off the transmission, making it easier to shift out of park [source: Rubenstein].

The emergency brake can also be used as an aid to manual transmission drivers to prevent rollback when starting on a hill. Pulling the emergency brake while stopped, and then letting it out as you release the clutch can be tricky, so you might want to practice this maneuver before depending on it. Make sure there's no one behind you if you've never done it before -- especially if your father is with you, and you only have a learner's permit.

It's easy to forget that the emergency brake is on if you don't use it often. To prevent driving off with the brake still engaged, try to set the brake as hard as you possibly can. Then leave an item on or around the lever, such as a cell-phone charger cord or a spare piece of paper.


To read the full article on How Stuff Works, click here.