Re: [MV] Silicone Brake Fluid - About Dean's comment.

Alan Bowes (
Wed, 20 Oct 1999 09:45:13 -0600

Richard Notton wrote:

> >Silicone brake fluid is 2% more compressible than glycol-based brake fluid.
> >You might feel the difference, I cannot.
> >
> It is a very small difference.

>From what I've read, it's 2X to 3X more compressible than glycol fluids (200%-300%).

> Not only that but the absorbed water will collect eventually, under severe
> stress this can boil making vapour (steam) and lead to total brake failure,
> however, when investigated the system will appear to be wholly operational
> again. Over here fluid change is a 3yr service item.

Yes, a blob of water in a hot wheel cylinder or caliper could flash into steam.
Plus, water collection in silicone fluids has been known to cause spot corrosion in
low spots in brake lines. It's essential to avoid the introduction of any water
whatsoever when converting to silicone fluid. One thing that is of some concern is
that some people have used isopropyl alcohol to flush their system. This could be a
very bad idea. Most isopropyl alcohol has about 30 percent water and other
ingredients in it.

> People with older British MV's should be aware that some are mineral OM13 fluid
> (oil) only, FV701's are confusing having been converted from OM13 to "Brake
> fluid" in some cases, FV 600 series and FV101 series are definitely mineral
> OM13. Using normal fluid in these will have all the seals swell and possibly
> disintegrate, theoretically these components were marked with a green splash of
> paint, but then the army has re-painted the whole vehicle several times when we
> get it.

I remember using the wrong brake fluid in a Land Rover about 20 years ago, and it
"softened" the seals to the point where they began to leak just a few days after
adding it. I had to rebuild the whole system with all new rubber parts.

> I wonder what bright spark designated the latest regular fluid to be DOT 5.1
> whilst the silicone is DOT 5, all the cans of 5.1 here have had to be over
> labelled with a warning that it is NOT silicone based.

Definitely a confusing designation.

Alan Bowes

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