You step on the brake pedal and the car stops. Seems simple enough, right? You don’t have to be a professional to understand a brake system. In fact, knowing a few things about how they work can help keep you safe. Here are a few things every driver should know about traditional car brakes.
How Car Brakes Work
Hydraulics: When you step on the brakes, the brake pedal lever amplifies the force of your foot to compress the hydraulic system. The master cylinder acts like a pump using a piston to push against the brake fluid. Pressure builds in the master cylinder, which is transmitted to the brake calipers or wheel cylinders via rigid brake lines and flexible hoses. The system is a closed system, that is, brake fluid doesn’t enter or leave. If you notice low-fluid level, but not below the “low” mark, do not top it off, but inspect your brake pads and shoes for wear. If the fluid goes below the low mark, you may have a brake-fluid leak, which should be checked and repaired immediately.
Friction: The actual stopping work of a brake system is done by friction material bonded to a disc brake pad or drum brake shoe. For disc brakes the brake rotor is squeezed by a caliper (looks like a clamp) holding a brake pad on each side. The squeezing forces the brake pads against the rotor and stops the vehicle. For drum brakes a pair of half-moon shaped brake shoes are pushed against the inside of the brake drum by an actuator called a wheel cylinder. The brake shoes are forced outward against the brake drum to stop the vehicle.
Boosting: Your foot pressure alone is not enough to stop your car safely, which is why it’s boosted, often vacuum boosted. Some older cars used hydraulic boosting, taking pressure from the power steering pump, while newer cars use an electronic booster. All three systems multiply the force you can put into the brakes, making it easier for you to stop your car safely. Keep in mind, even if you’ve heard it will save gas, don’t turn off your car to coast down that long hill. Downshift instead. All three brake boosting methods need to car to be running in order to work correctly.
Anti-Lock Brakes: When you’re learning to drive in the rain and snow, you’re often told to pump the brakes to keep the car from going into a skid — and this used to be true of older cars. Anti-lock braking systems (ABS), standard on most cars since the mid-1980s, have eliminated the need for pumping the brakes. Instead, the ABS module uses wheel-speed sensors look for a wheel locking up, using a high-seed solenoid valve to temporarily reduce pressure on that wheel. In this case the wheel doesn’t lock up and you can maintain control of your vehicle. The ABS system can do this far faster than any driver can pump their foot. The result is a controlled stop which keeps the tires at maximum grip without locking up.
It is worth mentioning that many hybrid and almost all electric vehicles use some sort of regenerative braking. Regenerative braking uses the electric motor as a brake to slow down the vehicle. It turns the motor into a generator so that the braking energy is put back into the battery pack and not wasted. For now though even these electrified vehicles still rely on a traditional hydraulic braking system.
Troubleshooting
Noise: Generally speaking, you should not hear any noise when using the brakes on your car. If you hear any noises at all — squeaking, squealing, grinding, knocking, whining, groaning — have your brakes checked immediately. Keep in mind, emergency braking or hard braking on loose surfaces may engage the ABS system, which has an activation noise that has been described as grinding, buzzing or groaning.
Vibration: When you step on the brake pedal, you should feel constant pressure feedback from the system. If you feel pulsation in your foot or vibration in the vehicle or steering wheel, you may have a rotor or drum problem, sometimes caused by overheating. If you feel a vibration, have your brake system checked. Note, though, that ABS activation is often accompanied by pedal vibration, which is normal.
Hard Pedal: If your brake pedal is harder to push than normal you may have a problem with the brake booster system. You can get a feel for what unassisted brake pedal effort feels like by simply pressing the brake pedal a few times with the vehicle shut off. The stored power assist pressure will be exhaust and you should feel the pedal become harder to push. Now you have a base line of comparison.
Soft Pedal: Air in the brake system is the most likely source of a soft brake pedal. Since brake fluid cannot be compressed but air can, the brake pedal feels soft. This can be fixed by a thorough bleeding of the brake fluid.
Low Pedal: If your brake pedal goes to the floor or close to it, you may have low brake fluid. Check your brake fluid reservoir (usually found on top of the master cylinder, but not always so check your owner’s manual) and add fluid if it is low. You may also have a faulty master cylinder which is allowing brake fluid escape past the internal piston. If the brake pedal starts off normal and slowly descends to the floor, the master cylinder is a likely culprit.
