Putting the Stop on Forward Motion
When driving, it’s second nature to stop your car at red lights, stop signs and when you’re ready to park the car. But sometimes, it’s also important that your vehicle be able to stop – quickly, to avoid hitting other cars, pedestrians or objects in the road.
For all of this you rely on your brakes.
The braking system is easily one of the most important system in your car. Brakes are such a basic function that it’s easy to take them for granted until it’s too late.
Applying the Brakes = Applying Great Force and Energy
When you step on the brake, your car transmits the force from your foot to its brakes through a fluid, commanding a stopping force ten times as powerful as the force that puts the car in motion.
On most cars, the front brakes are of the disc type, and the rear brakes are of the "drum" type, which use two semi-circular shoes to press outward against the inner surfaces of a steel drum. Older cars often had drum brakes on all four wheels, but many newer cars now have 4-wheel disc brakes.
Many Parts Go Into Stopping Your Car
The brake system contains the following basic components:
Disc brakes produce friction between the rotor and the pads mounted in the caliper attached to the suspension members with a clamping action. Inside the calipers, pressure generated by the master cylinder causes the pistons to press against the pads. The pads then rub against the rotor, which causes the car to slow.
Disc brakes are simpler, lighter and offer better resistance to water than drum brakes.
The brake drum is a heavy flat-topped cylinder, located between the wheel rim and the wheel hub. The linings of the brake shoes work on the inside surface of the drum. Once the brakes are applied, the brake shoes come in contact with the inside surface of the brake drums and slow the rotation of the wheels.
While most older cars have drum brakes on the rear wheels, newer models are more likely to use rear disc brakes.
The caliper works like a C-clamp to pinch the pads onto the rotor. One caliper is mounted to the suspension members on each wheel. The caliper is usually mounted onto the spindle, allowing it to deliver the torsional force of the wheel to the chassis via the control arms. Brake hoses connect the caliper to the brake lines leading to the master cylinder. A "bleeder valve" is located on each caliper to allow air bubbles to be purged from the system.
Wheel cylinders are where movable piston(s) convert hydraulic brake fluid pressure into mechanical force. As the driver pushes down on the brake pedal, pistons move within the master cylinder and pressurize the brake fluid in the brake lines and cylinders at each wheel. In turn, the fluid pressure causes the wheel cylinders' pistons to move which then forces the shoes or pads against the brake drums or rotors.
Parking (Emergency) Brakes
The parking brake (sometimes called the emergency brake) is a cable-activated system used to hold the brakes continuously in the applied position. The parking brake activates the brakes on the rear wheels. Instead of hydraulic pressure, a cable (mechanical) linkage is used to engage the brake shoes or discs. When the parking-brake pedal is pressed (or, in many cars, a hand lever is pulled), a steel cable draws the brake shoes or pads firmly against the drums or rotors.
"Anti-lock" (ABS) systems use computer-controlled valves to limit the pressure delivered to each wheel cylinder. If a wheel locks up, no matter how hard you steer you cannot affect the car's direction. With ABS, no matter how hard the pedal is pressed, each wheel is prevented from locking up. This prevents skidding (and allows the driver to steer while panic-braking).
Regular Maintenance Helps You Maximize Your Stopping Power
Regular maintenance on your car's brakes is just as important as it is to your engine. Have them checked at least once a year, more if you drive frequently in city traffic or live in a hilly area. Waiting until the brakes begin to grind can be more expensive, but a few simple steps will help keep your brakes in good working order.
- Never drive with the parking brake on.
- If you hear a high-pitched squeak when you apply the brakes, it’s time to get them checked. The squeak is actually a brake-pad sensor--a soft piece of metal that scrapes against the rotor when the brake pads need replacing.
- It’s always a good idea to check your brake fluid when you’re checking your other car fluids. If you notice that you’re adding brake fluid more than once every few months, there may be a leak somewhere. Bring your vehicle in for a complete brake system check.
Signs of Brake Trouble: When to Visit Your Technician
Things to look for when you apply the brakes:
- If the pedal slowly sinks down to the floor, you may have a bad master cylinder.
- If the pedal feels soft and mushy but gets harder when you pump up and down, your mechanic may need to bleed the brake lines to remove any air pockets.
- If the brakes pulsate when you step on them, the rotors may be warped.
- If the brake pedal sinks to the floor or gets soft when using the brakes on a long, steep downhill grade, that could be brake fade, which is when the brake fluid gets hot enough to boil. This problem tends to disappear once the brake fluid cools down.
Most important of all: Never drive the car for more than a short distance if your brake light comes on. If it does, check the brake fluid and make an appointment to have the brakes checked.