Volvo has had 4 wheel disc brakes for over 35 years. Now virtually every manufacturer has adopted 4 wheel disc brakes due to their reliable efficiency.   Yet many customers have little knowledge of how their disc brakes work. We hope to remedy that with the following primer on Disc Brakes.

We can divide the system into two parts, the mechanical system and the hydraulic system.

First let's look at the hydraulic parts. Here is a simplified diagram.

When you press on the brake pedal you start to move a piston inside the Master Cylinder. This function is much like depressing the plunger on a syringe. As you press down you displace brake fluid inside the master cylinder through the brake lines into the brake calipers.

The caliper wraps around the brake disc. The displaced fluid from the master cylinder begins to fill cylinders inside the caliper causing the pistons inside the caliper to be pushed out. These pistons then push the brake pads into the brake rotor or disc. Since the disc is solidly attached to the axle it rotates with the tires. If you stop the disc from turning you will stop the tires from turning.

On the right (above) is an animation of this process. The brake disc is not shown in this drawing for simplification. We will come back to that later when we examine the mechanical portion of the system.