Re: [MV] Enlarged brake drum (potential) problem

Richard Notton (
Wed, 27 Jan 1999 08:56:00 -0000

-----Original Message-----
From: jonathon <>
To: <>
Date: 27 January 1999 03:53
Subject: Re: [MV] Enlarged brake drum (potential) problem

>. . . . . . . . . . . . . . . . . . .

>I do purge the system with fresh stuff now and then however. As I
>understand it one of the benifits of conventional brake fluid is that
>abosrbs water which gets it out of the way, corrosion and freezing wise
>is. Silcone fluid does not have the same water absorbing
>or so I'm told.
I think we've been round this in the past, however.
The corrosion isn't the real problem with hydroscopic brake fluid, the
absorbed water over _many_ years can be sufficient to collect near the
wheel cylinder/disc pistons and with continued braking on a long, twisty
down hill stretch say, it is possible to boil the entrapped water before
the fluid creating a compressible gaseous bubble of steam plus dissolved
gasses and therefore no brakes, after the ensuing crash and some cooling
the brakes will be found to work perfectly.

Apparently this is the scenario which caused the untimely demise of
Princess Grace of Monaco - your Grace Kelly, formerly. There has been
one documented occurrence here and doubtless several non-recorded
instances; any non-compressible liquid will operate in a hydraulic
system, even water, until a non-desirable characteristic of the fluid
medium causes failure.

Most of the post-war UK fighting vehicles do not use "brake fluid" as we
know it but an ISO 15 hydraulic oil (OM 13) equivalent to a thin
aircraft hydraulic fluid of a bright red colour much like auto
transmission fluid, it is to be found not only in the brake circuits but
in all the hydraulic applications including clutch, steering, hydraulic
cranes etc., the component parts of these systems appear to use standard
commercial items.

(Southampton UK)

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