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The Gentleman's Express: Tech-Tips from the JIOC

Table of Contents

Silicone Brake Fluids

Author: John Bamberg

The following four major factors affect the rate at which water will be absorbed by the brake fluid:

(1) The degree of humidity.
(2) The passage of time.
(3) The care of the fluid.
(4) The system integrity.

Specification 116 of the Federal Motor Vehicle Safety Standard covers control of the brake fluids and hydraulic system mineral oils, as follows:

DOT 3: A world standard, glycol and an active chemical (attacks paint), hygroscopic, causes corrosion.

DOT 4: Totally compatible with DOT 3 with a boiling point some 50 degrees higher.

DOT 5: Only met with silicone fluids. Chemically inert, safe on paint, boils about 750 degrees! Compatible with existing fluids and systems. Legal since 1974.

It is recommended that at the next fluid change, a silicone fluid be considered. Bleed screws should be opened and the old fluid ejected by whatever means are available, air, foot pedal pumping. Refill with the new DOT 5 fluid, rebleed the system and then periodically change the fluid every two years.

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Contents copyright 2008, 2009 - Jody F. Kerr

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