This question was repeated in: May 2008, December 2009 and May 2010
Principle: It works on the principle of Pascal's law, which states that "The confined liquid transmits pressure intensity equally in all directions."
Working: When the driver depresses pedal, the effort is transmitted through rod to piston of master cylinder. The piston moves in the cylinder and compress return spring forcing out the fluid from the cylinder into brake line through a by-pass. Piston of a brake cylinders are acted upon by the fluid and press against shoes, bringing their linings tightly against the working surfaces of the drums as soon as the pedal is released, the return spring pushes piston back. At the same time, the compression springs of the brake shoe move pistons to their initial position and the fluid begins to the flow in the reverse direction.
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