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How Does a Braking System Work?

By: Kevin Watson MSc - Updated: 7 Aug 2013 | comments*Discuss
 
Braking System Handbrake Hydraulic Pedal

Effective brakes on a vehicle are crucial. But how does a braking system transfer the pressure of a driver’s foot on a pedal to the four wheels of a heavy vehicle surging along a road?

ABS

Vehicles have one of two braking systems: ABS (Anti-Lock Brake System) and non-ABS. But the basic principles of the systems are the same. Pressure on a vehicle’s brake pedal causes a rise in brake fluid pressure that in turn operates the brakes on the wheels.

ABS brakes also have a computer-based speed system that uses sensors on each wheel. These sensors note when a wheel is not turning as quickly as the others. ABS corrects the problem by adjusting the brake pressure across all four wheels to bring them back into harmony. As a result, a driver is less likely to lose control of a vehicle.

Front and Rear Brakes

On a standard car, the design of the front and rear brakes is different. Front brakes are usually disc brakes; rear brakes are drum brakes.

With disc brakes, brake pads apply pressure to a rotating disc. This pressure slows the disc and hence the wheel. Brake pads are usually a mix of materials such as steel, brass and copper bonded with a resin. Some high performance vehicles use ceramic brake pads. Either way, the pads wear down over time.

Rear brake systems have two curved “shoes” inside each drum. Wheel cylinders force the shoes against the inside edge of the drum and cause the wheel to slow down.

Hydraulic Force

Brake pads and brake shoes require force to work. This comes from hydraulics within a braking system. The control behind the hydraulics is the brake fluid. A driver controls the pressure of this with the brake pedal.

When a driver puts his or her foot on the brake pedal, the action transfers immediately to a brake master cylinder. The master cylinder, and the brake lines that connect the master cylinder to the front and rear brakes, are full of brake fluid.

Any increase in brake fluid pressure transmitted by the master cylinder causes caliper pistons at the end of the brake lines to move. These pistons force the brake pads and shoes against the brake discs and drums respectively.

As with any hydraulic system, the initial force – in this case the pressure of a foot on a brake pedal - multiplies significantly. Some vehicles increase this force still further with vacuum or hydro-boost systems. These give a driver greater control over the brakes for less effort. The condition of your brakes and the design of your car, together with your reactions as a driver can make a huge difference to your stopping distance.

Handbrake

A vehicle’s handbrake also forms part of the braking system. Using the same hydraulic principle as the foot brake, it operates the brake pads and shoes and holds them in position when a vehicle is stationary.

Maintenance

Brake pads and shoes wear out. A garage should inspect the condition of the pads and shoes, and the rest of the braking system, during a service. It’s also necessary to replace the brake fluid at certain intervals. A vehicle handbook has the relevant details.

Brake Fluid Leaks

On rare occasions, brake fluid leaks. This is obviously a serious matter because it can lead to brake failure. A leak will decrease the brake fluid pressure. A valve built into a vehicle’s braking system registers this drop and activates a brake warning light on the vehicle dashboard. If this light ever appears, take the vehicle to a garage without delay.

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