How Emergency Brakes Work

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.

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.

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.