Brake Fluid: Brake fluid is the liquid that transmits the force through pressure for the brake pedal to the brake lines. Basically the brake fluid does not compress so it transmits this force (pressure) without lost.
One of the worse enemy of brake fluid
is heat. If the brake fluid boils or there is a leak in your
system there will be a lost of this incompressibility and your pedal
travel will increase. Not all brake fluids are the same. Most
brake fluid has ethylene glycol as it main ingredient. Ethylene
glycol has lubricating capability for the rubber parts and has a
high boiling point. Moisture is another enemy of brake fluids.
All bake fluids will absorb moisture form the atmosphere,
this moisture lowers the boiling point of the fluid drastically.
This moisture also can effect the balance of the system casing
corrosion. A perfect example of moisture getting your system
is the early Corvette brakes where it was common to change the calipers
or a regular basis due to contamination and corrosion.
Silicone brake fluid has a higher boiling point (around 700 degrees F.) than the ethylene glycol base fluids, but the major disadvantages is not "hygroscopic". Hygroscopic? "Altered by the absorption of moisture" What this means is since it is not a glycol based, when moisture enters the system it is not absorbed by the fluid. This results in beads of moisture moving through the brake line, collecting in the calipers. Since it is not uncommon to have temperatures in excess of 212 degrees F. (the boiling point of water), this collection of moisture will boil causing steam and vapor lock, this in turn will cause system failure. Silicone (DOT 5) is also highly compressible due to aeration and foaming under normal braking conditions.
If you are changing from a glycol base fluid to silicone or the other way around. The two types do not mix so your system should be completely purged, disassembled and dried out. When the two fluids are mixed you will get a gummy substance and it will really mess up your system.
We recommend using a good DOT 3 fluid. Wilwood makes a hi-temp fluid with a minimum dry-boiling point of 570 degrees F Dry-boiling point is measure in its virgin non-contaminated state. Wet-boiling point is the temperature a brake fluid will boil after it is fully saturated with moisture. DOT 3 fluids have a minimum wet boiling point of 284 degrees F.
Brake fluid should be changed periodically due to contamination. Never mix different DOT brake fluids. Under racing condition you would change these fluids like changing your oil.
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