Image Gallery: Car Safety
Image Gallery: Car Safety

Image Gallery: Car Safety This one little lever can mean the difference between a car staying put or rolling into the house down the hill. See more car safety pictures.

Photo courtesy Juan Jose Gutierrez Barrow/istockphoto.com

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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.

Read on to discover how emergency brakes keep you from rolling down that hill.

Using your emergency brake when you park in San Francisco is a really good idea.

Isabelle Rozenbaum/PhotoAlto/Getty Images

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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].

We'll discuss the importance of knowing when and how to use emergency brakes in the next section.

Old-Fashioned E-Brakes

Back in the covered-wagon days, settlers faced quite the challenge when trying to navigate down steep hills or mountains. Wagon drivers often had to tie a large log to the vehicle to create drag. And as a precursor to modern emergency brakes, they would also tie up one wheel with chains [source: McLynn].

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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.

Emergency brakes can be dangerous if they're not properly used. Read on to learn how to use emergency brakes the right way.

When E-Brakes Fail, Emergency Brakes and Toilets?

In April of 2008, comedian Jerry Seinfeld was driving in a vintage Fiat when the brakes failed. In an attempt to stop the vehicle, Seinfeld engaged the emergency brakes. They didn't work. Seinfeld's vehicle continued on toward an intersection before he jerked the wheel and rolled the car. Luckily, he escaped the frightening adventure unharmed [source: New York Post].

Other vehicles, including trains, use emergency brakes as well. But sometimes, the system is slightly flawed. In November 2008, a Swedish train conductor had to turn off the toilets in his train for fear of setting off the emergency brake system. Turns out the e-brakes are connected to the toilets, so if too many people flush, the train can come to a shrieking halt [source: United Press International].

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Dangers of the Emergency Brake

Even though the emergency brake cable is housed in a protective sleeve, with infrequent use, the cable can become corroded and rusted. This can result in cable failure just when you need it the most. Normal use prevents buildup and keeps the cable in good condition, though you should have the emergency brakes routinely inspected, as they sometimes need to be tightened [source: wiseGEEK].

In cold temperatures, the emergency brake cable can become frozen and fail to release when the lever is disengaged. Parking in a garage or other protected area can help you to avoid this problem. But if you have to park outside and it freezes up, you should not attempt to drive your vehicle. Solutions include waiting it out or jacking up the car and using a hairdryer. The best option in freezing weather is to simply not use the emergency brake at all [source: USACE]. If you're on level ground in a manual vehicle, put the car in first or reverse and skip the e-brake.

­Be aware that in some vehicles, the emergency brake engages the front brakes, not the rear brakes. Knowing which brakes are set and properly chocking your vehicle wheels will protect you in situations where you must jack up the vehicle. Refer to your service manual before you raise the car. Believing the rear brakes are engaged when they aren't can be extremely dangerous.

Now onto the big question: Is using the emergency brake safe when the other brakes fail? Yes and no. Pulling the brake lever quickly will cause the vehicle to fishtail, lock up or skid, essentially removing control of the vehicle from the driver. But if you're ever in the highly unlikely but extremely serious situation of having your service brakes fail to function, try to stay calm and pull the emergency brake lever up slow and steady, bringing the vehicle to a longer but more controlled stop.

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Lots More Information

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Sources

  • Crowley, Kieran. "Seinfeld's Car Flips." New York Post. 04/03/08 (Accessed 11/06/08) http://www.nypost.com/seven/04032008/news/regionalnews/seinfelds__car_flips_104778.htm
  • Lexus Technical Training, Section 6, "Parking Brake" 11/02/2008 (Accessed 11/05/08) http://www.autoshop101.com/forms/brake06.pdf
  • McLynn, Frank. " Wagons West: The Epic Story of America's Overland Trails." Grove Press. 2004
  • Nice, Karim. "How Disc Brakes Work." How Stuff Works. (Accessed 11/05/2008) http://auto.howstuffworks.com/disc-brake3.htm
  • Ofria, Charles. "A Short Course on Brakes". The Family Car. (Accessed 11/05/08) http://www.familycar.com/brakes.htm#Parking%20Brakes
  • Owen, Clifton. "Today's Technician: Automotive Brake Systems Classroom Manual, 3rd Edition." Delmar Cengage Learning. 2003
  • Rubenstein, Larry. "Auto-Scanner: Use That Emergency Brake." The Eagle-Tribune.10/18/08 (Accessed 11/06/08) http://www.eagletribune.com/pubiz/local_story_292225308.html
  • Smith, S.E., "How Does an Emergency Brake Work?" wiseGeek. (Accessed 11/05/2008) http://www.wisegeek.com/how-does-an-emergency-brake-work.htm
  • United Press International. "Trains shuts toilets to avoid stopping." 11/04/08 (Accessed 11/05/08) http://www.upi.com/Odd_News/2008/11/04/Train_shuts_toilets_to_avoid_stopping/UPI-15731225827879/
  • U.S. Army Core of Engineers. "Cold Weather Driving Tips." (Accessed 11/06/08) http://www.nad.usace.army.mil/cold_weather_driving_tips.htm
  • U.S. Department of Transportation. "Federal Motor Vehicle Safety Standards and Regulations." Revised March, 1999. (Accessed 11/05/08) http://www.nhtsa.dot.gov/cars/rules/import/FMVSS/
  • Zangari, Paul. "The Push-button Parking Brake." Motor Age. 07/01/08 (Accessed 11/02/2008) http://motorage.search-autoparts.com/motorage/Good+Reads/The-Push-button-Parking-Brake ­/ArticleStandard/Article/detail/526978?contextCategoryId=1079