How does an emergency brake work?

The parking brake or emergency brake is engineered to operate the rear brakes by way of a series of steel cables that are connected to either a hand lever or a foot pedal.

The hand lever or foot pedal is typically manufactured with a ratcheting action so that the lever or pedal can be partially engaged and locked in place.

To release the brakes, a separate control is often fitted (for example, a button on the handle or a separate release handle for a foot brake). In other instances, the release is accomplished by pushing the brake all of the way through its travel.

Parking brake cable power
Why use a cable arrangement? The emergency or parking brake system is completely mechanical and, by design, effectively bypasses the entire hydraulic system. In the event of a total brake failure (for example, a ruptured hydraulic line), the car or truck can still be brought to a safe stop.

How the car or truck comes to a stop depends on the type of brakes it has:

Drum brakes: On vehicles with drum brakes on the rear axle, the parking brake cable pulls on a lever mounted within the rear brake drum. The cable is connected directly to the brake shoes, and upon application, it physically pulls the shoes into the spinning drum to create stopping friction.

Disc brakes: Disc breaks mounted on the rear axle are slightly different. There are typically two forms of park brakes used on disc-equipped cars or trucks: One type is engineered so a miniature drum brake system mounts within the rear brake rotor. The brake shoes incorporated in this system connect to a lever that is engaged by the park brake lever or foot pedal. Once engaged, the brake shoe applies against the small drum within the rotor and stops the vehicle. Another arrangement commonly found on four-wheel disc brake cars (particularly those with sliding single piston “floating” calipers) is based on a device that mechanically forces the caliper piston against the brake pad. In turn, this moves the brake pads (and, of course, the floating caliper) toward the spinning rotor, effectively stopping the car.

Parking brake equalizer
Regardless of style, some sort of cable system is required in order to physically link the emergency brake foot pedal or hand lever to the rear brakes. In most vehicles, there is a form of parking brake equalizer arrangement. It is designed to equalize the forces to both the left and right rear brakes as the lever or pedal is applied. It is essentially a “Y” connection that hooks to a set of shielded cables from each rear brake.

Linking the equalizer (“Y” connection) to the pedal or lever is another cable, often shielded. Adjusted properly and used regularly to avoid seizure from corrosion, the emergency brake system is another simple but effective device found on your car or light truck.

System limitations
There’s a catch to the system: In many vehicles, the emergency brake sees little or no use (case in point, cars and trucks with automatic transmissions). As pointed out, lack of use causes the cables to corrode. This is particularly common on the shielded cables where the actual cable mechanism glides through a tough outer shield. Trapped water, salt and road debris can freeze the works up solid.

The solution is simple: Use the emergency brake (setting it as a park brake) regularly. You won’t regret it.

For a closer look at what brings your car to a grinding halt in an emergency situation, check out the following photos:

There are two common ways to apply an emergency brake system: using an auxiliary foot pedal or by way of a handle lever (as shown).

Up close you can see just how a common foot brake pedal for an emergency brake system is built. There’s a ratchet action inside (see the pointer), along with a separate ratchet release lever. Some foot pedal systems have an auto-release, where depressing the foot brake a second time deactivates the system.

Here is a secondary release lever found on one particular foot brake system.

A series of cables link the park brake to the rear brakes. The heavy shielded cables (shown here) attach to the rear brakes while a (much) lighter unshielded cable forms the basis for the “Y” or equalizer.

In operation, the cable acts against the rear brakes. In this case, it is designed to force the brake shoes outward, applying them to the drum. That action effectively stops the car. The same principle, but with varying mechanics, is used with disc brake systems.

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