The braking system contains many moving parts, and because brakes work by creating friction to slow or stop the vehicle, many of these parts wear a little each time the brakes are applied.
For example, brake pads contain 'friction material' – a material with a rough surface which is forced onto the brake disc to slow it down, or stop it completely, during braking. This rate that this friction material wears is dependent on many factors, including whether you do more 'stop-start' town driving or motorway miles, where the brakes have to slow or stop the vehicle from higher speeds. Driving style is another factor.
Your brakes will usually wear gradually so you might not notice a sudden difference, however there are a few ways in which you can tell that your brakes should be checked:
Brake fluid is the lifeblood of the braking system. When you press the brake pedal this force is transferred through the brake system to the caliper or wheel cylinder by the brake fluid.
Brake fluid is designed to withstand normal brake system operating temperatures, however under the extremely high temperatures caused by heavy or prolonged braking, brake fluid can deteriorate and lose its effectiveness – and if the temperature rises above its boiling point it can even lead to total brake failure.
As it moves around the brake system during its lifespan, brake fluid also absorbs moisture and gradually becomes contaminated, significantly reducing its effectiveness. We can check the levels of contamination, however most vehicle manufacturers recommend that brake fluid should be replaced every two years.
Many parts in the brake system are held in place under tension using springs and clips to minimise the amount that they can move around or vibrate when the vehicle is moving.
Over time it's normal for these accessories to lose tension. In fact over one or two years the tension can reduce by as much as 50%, rendering them much less effective. This can lead to an increase in brake squeal or, if they break, can even cause the brake pads or shoes to become loose or dislodge.