Car brake system – driving licence theory

Dual-circuit brake system

Dual-circuit brake systems entail the footbrake being divided into two independent parts. If one circuit (brake for 2 wheels) fails, the second circuit (remaining 2 wheels) functions as normal. This increases the level of safety and is a feature of all apart from the oldest of cars.

Modern cars have hydraulic brakes. This means that the braking force is transferred from the pedal to the brakes with the help of a special brake fluid.

Wheel removed from a car.

Wheel removed from a car with disc brakes. The brake caliper is the grey part above the disc to the left.

When the brake fluid reaches the wheel, it operates the brake. There are 2 different types of brakes: disc brakes and drum brakes.

Disc brakes

Disc brakes have an open brake disc and a caliper which is pressed against the disc when you brake. These brakes are normal for the front wheels, but have also become increasingly common in use on all wheels as they are often more effective than drum brakes.

Drum brakes

Drum brakes have a closed construction consisting of a round drum. Inside the drum are brake shoes which are pressed against the drum when you brake. These brakes are commonly used for the back wheels.

ABS brakes

Anti-lock brakes (ABS) help you to maintain control of the car (manoeuvrability) in conjunction with forceful braking. The braking distance can be decreased, but in certain cases may be increased.

How ABS brakes work

  1. You press down the brake pedal hard, which causes the wheels to lock (car glides forward, tyres “squeal”).
  2. The ABS system senses instantly that the wheels have locked (as they are not turning).
  3. The ABS system releases some of the pressure on the brakes so that the tyres begin to turn.
  4. The ABS system then adapts the braking force so that it is as strong as possible without becoming excessive and locking the brakes.

As the wheels are not locked, you can steer in conjunction with braking with ABS. This is very important if you need to swerve to avoid something.

Confusion and ignorance among drivers regarding ABS

When you brake hard with a car which features ABS, the pedal may begin to stutter and pulsate (it sounds as if something is wrong). This is entirely normal, however, as this is how the ABS system works!

You should continue to hold down the pedal as hard as you can, without releasing, however strange it feels.

Drivers releasing the brakes is, however, still common – so much so that there are Brake Assist (BA) systems which, in connection with forceful braking, retain the pressure on the brake pedal despite the driver releasing it.

Faulty brakes – test

In order to test the brakes, press the pedal down hard for 20 seconds and check for the following:

  • If the brake pedal sinks very low, this indicates wear.
  • Should the pedal continue to sink slowly, despite the fact that you have reached the “bottom”, this means there is probably a leak in the brake system. This poses a very serious traffic hazard and must be rectified immediately.
  • If the pedal feels springy, this may be due to air in the brake system. Take the car to a shop to have this rectified.

It is also important to test the brakes once in a while. If the car is pulling to one side, it is time to take it to the shop.

It is especially important to test the brakes after washing the car, as the water has a negative impact on them. Forceful, controlled braking will dry up the moisture.

Brake fluid

Brake fluid

Brake fluid is normally yellow and is topped up in one of the smaller reservoirs in the engine compartment.

If you make a kink in a garden hose, this leads to a build-up of pressure as the water has nowhere to go. Hydraulic brake systems work in the same way.

The brake lines are filled to maximum capacity and when you press on the brake pedal, the brake fluid wants to exit via the other end. This is not possible, as the system is closed. The result is that the fluid presses on the brakes so that the car stops.

As the brake fluid is liquid, the brake lines (which the fluid travels through) can be curved to fit the car’s form.

Changing brake fluid

One problem with brake fluid is that it attracts moisture/water, which can lead to a deterioration of its properties. This means that it needs to be changed every two years as a rule.

Brake servo (vacuum servo)

Just like power steering, the brake servo helps you by reducing the force required from you when depressing the brake pedal. The brake servo only works when the engine is running.

Test to see if the brake servo is working

  1. Pump the brake pedal a few times with the engine switched off.
  2. Start the car with the brake pedal depressed.
  3. If the pedal sinks when the engine starts, the servo is working as it should.

Parking brake (handbrake)

The handbrake is there to stop the car from rolling when it is parked. This normally applies the brakes to the back wheels. Things to consider with the handbrake:

  • Do not use if it is cold and humid, as there is a risk that it will freeze in place.
  • It may seize up if you do not use it regularly.
  • In addition to the parking brake, it is good to put the car in first gear, as this further reduces the risk that the car will roll.
  • Check to see whether the parking brake is working:
    • Set the car rolling down a hill and then pull on the brake.
    • Try to drive with the brake on.

Practice theory tests

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Last updated 2017-09-08.