In 1918, a young inventor named Malcolm Lougheed (who later changed the spelling of his name to Lockheed) applied hydraulics to braking.  He used cylinders and tubes to transmit fluid pressure against brake shoes, pushing the shoes against the drums.  In 1921, the first passenger car to be equipped with four-wheel hydraulic brakes appeared — the Model A Duesenberg.  Carmakers as a group were not quick to adopt hydraulics.  Ten years after the Model A Duesie, in 1921, only Chrysler, Dodge, Desoto, Plymouth, Auburn, Franklin, Reo, and Graham had hydraulic brakes.  All the others still had cable-operated mechanical brakes.  In fact, it was not until 1939 that Ford finally gave in, becoming the last major manufacturer to switch to hydraulic brakes.

Side Bar:  Studebaker introduced a hydraulic four wheel braking system as an option in 1925, but failed to execute it very well and dropped the option for 1926.  Hydraulic brakes were not re-introduced at Studebaker until 1935.