Quote:
Originally Posted by unkl300d
Hi Bill, interesting anecdote about silicone brake fluid.
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Yes, many crazy stories about changing to silicone fluid, many spread by auto parts counter guys. Some claim that if the silicone fluid touches glycol, mysterious chemical reactions occur. One (anal) engineer car hobbyist found that humorous so ran his own tests, mixing the fluid in jars and leaving them set for a year. No mingling or chemistry occurred. Yes, any drops of leftover glycol w/ moisture could be a place for corrosion, though without atmospheric oxygen, I don't envision how that chemistry could work. When I have converted to silicone (all but one of my vehicles), it has been when changing other parts, so flushed ethanol thru the tubing and blew it out with air. You could also first bleed thru fresh glycol fluid (much cheaper than silicone), so any residual will not have absorbed moisture to worry about. Once you see the blue dye of the silicone, you have swept most of the glycol out (though fluid dynamics doesn't quite work like that, see "no slip at wall").
It was easier to source silicone when the U.S. military required it (termed "Brake Fluid Silicone" BFS). Low maintenance made sense for equipment which could be in remote areas. But, they changed to glycol a decade or so ago, claiming "easier to source", though I'm guessing cost was more a factor. I used to buy it by the gallon, searching by MIL number, but surplus is mostly gone now. Many current motorcycles use it, if you don't mind buying by the pint (costlier). Re seal compatibility (another fuss), it is more benign than glycol (which is a paint remover), indeed some 1950's British cars required silicone brake fluid since glycol fluids attacked their seals.