Disc Brake Servicing & Replacement Enquiry:-

Disc Brake Pad Replacement and Routine Service

How Brakes Work

If you need to stop a car from 70mph your brakes absorb enough energy to make 10 cups of coffee or boil 2.3 litres of water

Here's the science:

The Ford Focus is a popular family car and has a curb weight of approximately 1430kg. If it has 5 gallons of petrol or diesel fuel onboard that adds a further 20kg.
Each Passenger Will add about 70kg.

So, A Ford Focus with 2 adults onboard has a mass of 1590kg

Let's say our Ford Focus is travelling at 30mph (13.4m/s)

It has a total kinetic energy of:
0.5 x 1590 x 13.4 x 13.4 = 143,000 Joules = 143kJ

Or to put it another way - When you travel at 30mph and have to stop; your brakes need to absorb/remove enough energy to boil 2 cups of water.

Virtually all of this energy is absorbed and converted into heat between the high friction surfaces of your brake pads and your brake disc rotors.

Hydraulic Brakes

Most modern brakes use a hydraulic system.

As you apply pressure to the brake pedal, that force presses down a piston (The Master Cylinder) increasing the pressure on the brake fluid in the piston chamber.

The hydraulic brake fluid can't compress and is forced through a narrow tube in the piston chamber. It travels along brake pipes until it emerges into a second chamber that also operates a piston (The slave cylinder).

The slave cylinder piston moves outwards and operates a brake disc caliper that pushes a brake pad coated in a high friction material against a brake disc that is attached to a wheel.

As the brake pedal is pressed down - Friction increases between the brake pad and brake disc to slow down the vehicle

Most of the work of stopping the vehicle is handled by the front wheels so pressure is applied equally from the master cylinder to two slave cylinders or caliper pistons

Servo Assisted Braking - Power Brake

Servo systems take the effort you apply to the brake pedal and multiply it by operationg a servo mechanism.

Servo Assisted Brakes can operate when the engine is running by using engine vaccuum or a vaccuum pump

A chamber with a diaphragm has a vaccuum applied equally to both sides.
When you press the brake pedal a valve operates allowing air to enter a chamber on one side of the diaphragm neerest the brake pedal. The difference in pressure is proportional to the force applied to the brake pedal and operates the brake caliper to assist braking

If the engine is not running or the diaphragm fails then only the hydraulic braking system will work and there will be no brake assist making the brakes very difficult to apply.

ABS Brakes - Anti Lock Braking Systems

Braking efficiency is greatest just before each wheel locks and a skid occurs

At this point you still have control of the vehicle while during a skid you can lose control.

Anti-lock brake systems prevent the wheels from locking by rapidly releasing then pumping the brakes whenever the system detects wheel lock.

Usually, only the locked wheel is pumped. Full braking continues on the other wheels.

This allows the driver to maintain full steering control even in wetor icy conditions

ABS ECU - Electronic Control Unit

The Antilock Braking System is controlled by a mini computer or ECU that monitors wheel speed sensors mounted on each wheel.

The ECU detects the moment when the wheel stops rotating and operates an hydraulic actuator to release the brake pressure.

The wheel starts to rotate and braking pressure is applied once more. This process repeats to maintain optimal braking without wheel lock

The ABS fails safe - In other words - If a problem occurs with the system, the brakes will still operate normally only without the benefit of ABS


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