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Brake System

Basic Description

Most brake systems use a layout very similar to that seen here, comprising the pedal, a booster, master cylinder, hydraulic lines and …

Basic Description

Most brake systems use a layout very similar to that seen here, comprising the pedal, a booster, master cylinder, hydraulic lines and hoses, and calipers or wheel cylinders that apply pressure to a pad coated in friction material so that it pushes against a rotating disc or drum. Clicking on any of the links will take you to an animation explaining how it works, and highlighting the common failures for each part.

Technical Description

The purpose of the system is to convert the energy of the moving vehicle into heat in order slow the vehicle down. Although some hybrid vehicles are beginning to convert kinetic energy into stored electricity, all vehicles still use a brake system similar to that shown here.The pressure from the drivers foot (with assistance provided by the vacuum booster) is initially converted into fluid pressure in the brake lines by the brake master cylinder. Brake fluid is a hydraulic fluid that is stable in volume under a wide range of temperatures – it does not expand as it heats up.The pressurized brake fluid forces the pistons in the brake caliper outwards, so that they press against brake pads. The pads squeeze the surface of the rotating brake disc, causing it to slow, and generating heat. The heat is dispersed through cooling fins inside the rotor to prevent the rotor and pads from overheating.

Disc Brake

Basic Description

The disc brake system consists mainly of a brake caliper, brake pads, and a brake rotor.

Basic Description

The disc brake system consists mainly of a brake caliper, brake pads, and a brake rotor.

Technical Description

Almost all vehicles use disc brake systems, particularly on the front wheels. Disc brakes work by squeezing together a pair of brake pads on the rotating brake disc or rotor. The device that squeezes the pads together is called the brake caliper. Disc brakes can develop problems such as warped rotors – which cause the steering wheel to shake when the brakes are applied, or may become rusted and fail to apply or release evenly, causing uneven or accelerated brake pad wear.

Drum Brake

Basic Description

The drum brake system consists mainly of a hydraulic wheel cylinder, brake shoes, return springs, and a brake drum.

Basic Description

The drum brake system consists mainly of a hydraulic wheel cylinder, brake shoes, return springs, and a brake drum.

Technical Description

Drum brakes are generally used to stop the rear wheels on trucks and lower performance cars. The drum is connected to either the rear axle or a wheel hub, and the wheel is attached to the drum. The wheel cylinder is the device in the top of the picture between the tops of the red brake shoes. Clicking Apply Brakes shows how the pistons in the wheel cylinder move outwards when the brake fluid is pressurised. This forces the brake shoes – the red/orange half circles on each side – to move outwards, forcing them to push against the inside of the brake drum and slowing then stopping the wheel from turning.The orange friction material on the brake shoes wears out as the brakes are applied. Removing the brake shoes involves dismantling the springs and clips that hold the red brake shoes in place. When installing new shoes it may be necessary to also replace the springs or hardware to keep the shoes in place properly.

Parking Brakes

Basic Description

The parking brake includes all components in the drum brake system. In addition to this, it also includes a cable, and a lever to apply the …

Basic Description

The parking brake includes all components in the drum brake system. In addition to this, it also includes a cable, and a lever to apply the parking brake.

Technical Description

When the drum brakes are applied by the drivers foot on the brake pedal, hydraulic fluid forces the wheel cylinder to expand and apply the brakes. The parking brake is almost always operated by a cable, not by brake fluid pressure. Clicking ‘Apply Parking Brake’ shows how the cable pulls a lever which forces the brake shoes to spread apart, pushing them against the inside of the brake drum to stop the vehicle from moving. The parking brake also operates the auto-adjuster inside the brake drum, which is the bar that goes between the two brake shoes – located in this diagram just below the grey and black wheel cylinder. The star shaped wheel or gear is attached to a threaded bolt. Each time the park brake is applied and released, an arm tries to turn that star gear to ensure that the brake shoes remain close to the drum, but not touching when the brakes are released.Rust inside the brake drum can cause the brakes not to adjust automatically, which can cause the park brake to become inoperative or the brake pedal to have too much travel if the shoes have to move a long way before reaching the drum.The Other common problems experienced with the parking brake system is when the cable that operates the park brake does not move freely inside its casing. This can cause either the cable to not allow the brake to be applied, or it may allow the brake to be applied but not move back freely to allow the brake to release – causing rapid wear of the brake shoes.

Leaking Axle Seal

Basic Description

On rear wheel drive vehicles, the axle is held inside a tube lubricated with differential gear oil. There is an oil seal to prevent the gear oil from …

Basic Description

On rear wheel drive vehicles, the axle is held inside a tube lubricated with differential gear oil. There is an oil seal to prevent the gear oil from entering the brake drum.

Technical Description

When this seal leaks, gear oil drips inside the brake drum, and contaminates the brake shoes. To repair this, the axle usually needs to be removed, a new seal installed, brake shoes replaced and all other components need to be cleaned and degreased or replaced. A leaking axle seal can also cause the differential fluid to be low, potentially causing damage to the gears inside the differential.