How Hydraulic Brakes Work...

It was during the mid 1930's that hydraulic brakes were introduced by most car manufacturers. Prior to that with a few exceptions, mechanical brakes were the norm, which meant all of the brake shoes located in the drums behind the wheels were activated by way of mechanical rods connected to the brake pedal. Those rods needed constant adjustment in order to make sure the vehicle stopped straight. If the rods were not all adjusted equally the vehicle would tend to pull in one direction or the other causing the car to swerve,  as unequal pressure was applied the brake shoes.

Hydraulic brakes solved a lot of the problems associated with mechanical brakes along with providing more stopping power with less effort. After 80 years we take hydraulic brakes for granted but they were a revolutionary upgrade at the time of their introduction.

Now that you know a little of their history it's time you understood the principles of how hydraulic brakes work.  So... here is a training film from 1936 that explains just that. Watching this movie is much more fun than reading some old greasy shop manual. Enjoy...