A New Engineering Approach for Converting Vehicle Brake System to Silicone Brake Fluid

Brake Fluid, Silicone (BFS, MIL-B-46176), which was developed by the U.S. Army Belvoir Research, Development and Engineering Center (BRDEC) in conjunction with industry, was approved in 1980 for retrofit of all U.S. Army vehicles. The approved method for conversion was a flush-and-fill procedure. This method, however, will leave residual polyglycol fluid in brake systems due to the following interdependent reasons: (a) The geometry of the wheel cylinders (bleeders at the top), (b) the immiscibility of the two fluids, and (c) the lower density of the silicone.

A project in this Laboratory resulted in the development of a method which is effective in the complete removal of all polyglycol fluid. The method involves the use of an intermediate fluid (2-ethylhexanol, 2-EH) whose properties are such that a reversal of the phases is induced. This method is thus based on the existence of an isopycnic tie line in the phase diagram of the binary phase system. This phase diagram shows a high phase boundary.