Hydraulic brakes

Almost every car, two-wheeler and light truck sold in India stops with hydraulic brakes. Instead of rods or cables, a liquid carries your effort from the pedal (or lever) to the wheels. Brake fluid cannot be squeezed smaller, so pressure applied at one end of a sealed pipe appears at the other end straight away, and equally at every wheel.

• You press the pedal; a lever and, in most cars, a vacuum booster multiply the push.
• The pedal moves a piston inside the master cylinder, raising the pressure of the fluid.
• Steel pipes and short flexible hoses carry that pressure to each wheel.
• At the wheel, a caliper piston (disc brake) or wheel cylinder (drum brake) is pushed out, pressing friction material against the spinning disc or drum.
• Release the pedal and springs and seals pull everything back, and the fluid returns.

The clever part is Pascal's principle: pressure is the same everywhere in the fluid, so force depends on piston area. The master cylinder piston is small and the wheel pistons are large, which is why a light foot can stop a heavy car. Cars use a tandem master cylinder with two separate circuits, usually split diagonally, so a leak in one still leaves two wheels braking. Motorcycles have a small master cylinder on the handlebar for the front brake and another by the right footpeg for the rear.

What you notice is a firm, progressive pedal. A spongy pedal usually means air or old, moisture-laden fluid in the system, which is why the fluid is replaced at the interval in the service schedule.