[Mgs] brake fluid

PaulHunt73 paulhunt73 at virginmedia.com
Mon Oct 29 02:38:44 MDT 2012

That's exactly it.  Suppliers statements of "Silicone Brake Fluid repels
moisture so, unlike standard polyglycol brake fluid, it never needs
changing. Rust and corrosion are inhibited because moisture is kept out of
the system ..." are a complete nonsense.  The same amount of water gets into
MGB systems filled with silicone fluid as it does with glycol.  It still
migrates to the ends of the system i.e. the callipers and slaves, and hence
still reduces the boiling point particularly in the callipers, as well as
causing localised rusting.  It may well not mix with water, but it absorbs
air, which results in a spongy pedal.  Water in DOT3 and 4 is as
uncompressible as brake fluid.  It's original USP was a higher boiling point
than DOT4, as well as not damaging paint.  Now DOT5.1 has a higher boiling
point than DOT5 (and Castrol LMA (Low Moisture Absorption) always did) it's
only benefit is with the paint.  Some time ago I read that as soon as
someone came up with a way of completely flushing all traces of silicone
from hydraulic systems the American military would be ditching silicone in
favour of DOT5.1.

Humidity isn't the only factor.  Temperature is as well, and the rapidity 
and frequency of
changes from cold and dry to warm and wet, where warm moist air condenses
out on everything, something we in the UK at least get very frequently, and
in any season.

Whilst the Workshop Manual specifies changing all hydraulic *seals* at 36 
k/months (albeit North America only) it doesn't mention fluid.  Fluid is 
obviously (?) replaced at the same time, and it probably does no harm to 
flush some out of each calliper and slave annually.


----- Original Message ----- 
> Water vapour still comes into the system, so finally can create rust into
> the cylinder bores.

More information about the Mgs mailing list