Brake lines are steel tubing with copper and lead coatings to prevent rust and corrosion. As the brake pedal is depressed, it moves pistons within the master cylinder and forcing hydraulic brake fluid throughout the brake system and into the wheel (or brake) cylinders.
The pressure placed upon this fluid causes the cylinder pistons to move, forcing the brake shoes or friction pads and brake drums or rotors to slow the vehicle.
Brake fluid is a type of hydraulic fluid used in brake applications in motorcycles, automobiles, light trucks and some advanced bicycles.
It is used to transfer force under pressure from where it is created through hydraulic lines to the braking mechanism near the wheels.
It works because liquids are not appreciably compressible. Braking applications produce a lot of heat so brake fluid must have a high boiling point to remain effective and must also not freeze under normal temperatures. These requirements eliminate most water-based solutions.
Although almost all road-going vehicles have only two brake pads per caliper, racing calipers utilize up to six pads, with varying frictional properties in a staggered pattern for optimum performance.
Early brake pads (and shoes) contained asbestos. When working on an older car's brakes, care must be taken not to inhale any dust present on the caliper or drum.