Re: Silicone brake fluid

[Don Hoefer <hoefer@eng.pko.dec.com>]

Gary G. Erickson wrote:
>
> ... DOT5 has an extreme tendency to
> absorb either air or water, so that standard flushing and bleed
> techniques must be employed much more often than normal.
> 

It is my understanding that DOT5 brake fluid does not absorb water.
If (when) any water gets into the brake system, it puddles, whereas
conventional brake fluid will absorb and distribute it.  The water
will raise the freezing point and lower the boiling point of con-
ventional brake fluid, and, conversely the brake fluid will raise
the boiling point and lower the freezing point of the water.  This
will not happen with DOT5.  The water will freeze or boil wherever
it is in your system and the DOT5 fluid will be unaffected.  Your
brakes will not be unaffected to say the least.

Therefore the system must be flushed much more often.

> IMO, it would seem that for the amount of work involved, for a normal
> street car, to stick with a good quality, high performance DOT4 fluid
> such as Castrol GT-LMA or the ATE Super Blue.
> 

I understand that DOT5 is popular in well maintained classic
or collectable cars that don't get driven much and live a life
of shelter.  In that case you don't want a brake fluid that will
absorb water and distribute it (osmosis) throughout the system
during long periods of storage.

Don Hoefer
'82 Coupe