All 1959 Buicks with power brakes used a one-year only Delco-Moraine single reservoir system with the master cylinder mounted below the toe board. NOS or rebuilt cylinders or parts are virtually nonexistent making rebuilding the existing cylinder the only option. The power brake master cylinder and booster was rebuilt by Power Brake X-Change (http://www.powerbrakex-change.com/), all new pre-bent stainless steel brake lines as well as rubber brake lines came from Classic Tube (http://www.classictube.com/) and fit perfectly. New wheel cylinders, brake linings, and springs came CARS (http://www.oldbuickparts.com/).
Below is explanation of the 1959 Buick Power Brakes, standard on the Electra 225, from the 1959 Buick Facts Book (Click on Picture to Enlarge).
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~ Tom Sidoti
1959 Buick Electra 225 Convertible