Shane Ingate said:
>>I will go so far as to advise most strongly against using DOT 5
(silicone) fluid.
>>DOT 5 has a very nasty habit of accumulating water
Shane, there seems to be some confusion, please correct me if it's mine.
DOT 5 (silicone) brake fluid is NOT hydrophilic. It will not absorb
water as does DOT 3 and 4. Advantages are that it will not promote
internal corrosion of the brake system. Old DOT 3 and 4 will absorb
atmospheric moisture, thereby corroding internal bores and rusting out
lines from the inside.
The web page (http://www.vtr.org/maintain/brake-fluids.html) mentions
that DOT 5 can lead to corrosion because it is hydrophobic, stating that
moisture in the system will tend to puddle. How would this moisture get
in the system, once it's filled with a hydrophobic fluid? OTOH, DOT 3
and 4 will themselves absorb moisture from the atmosphere, spreading it
throughout the system to MC and caliper bores, and steel lines. In
addition, as they absorb moisture the boiling point drops dramatically,
that's why racers replace their glycol based fluid after every race.
I have used DOT 5 fluid for 10 years in various cars, including those
that I autocross. I've never had a problem with it. My changeover
procedure has always been to simply drain, fill and bleed, as instructed
by the manufacturer. I have, on one occasion, seen globs of glycol
based fluid float to the MC resovoir after a year or so, but it didn't
seem to cause any problems and the manufacturer didn't believe it to be
any type of hazard. I certainly have never seen any solid matter form.
It is more expensive, and a little harder to bleed properly, but then I
don't have to redo the job every year, and other sources indicate that
it should prevent pitting and corrosion in my brake system.
Tom Gentry
Life is too short to drive boring cars!
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