by clee » Sat May 13, 2006 6:55 am
Brake Fluid Application Guide and Tips :
Due to the extreme operating temperatures of a high performance brake system, standard 'off-the-shelf' brake fluids are not recommended. Of critical importance in determining a fluids ability to handle high temperature applications is the Dry Boiling Point and compressibility.
The Dry Boiling Point is the temperature at which a brake fluid will boil in its virgin non-contaminated state. The highest temperature Dry Boiling Point available in a DOT 3 fluid is 572 F
The Wet Boiling Point is the temperature a brake fluid will boil after it has been fully saturated with moisture. The DOT 3 requirement for wet boiling point is a minimum temperature of 284 F.
There are many ways for moisture to enter your brake system. Condensation from regular use, washing the vehicle and humidity are the most common, with little hope of prevention. Glycol based DOT 3 & 4 & 5.1 fluids are hygroscopic; they absorb brake system moisture, and over time the boiling point is gradually reduced.
We do not recommend using DOT 5 fluid in any racing applications. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers . It is not uncommon to have caliper temperatures exceed 200 F, and at 212 F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel. DOT 5 fluid is best suited for show car applications where its anti-corrosion and paint friendly characteristics are important.
Whenever you add fresh fluid to your existing system (never mix fluids of different DOT classifications), it immediately becomes contaminated, lowering the boiling point of the new fluid.
For maximum performance, start with the highest Dry Boiling Point available, flush the system completely, and flush it regularly, especially after severe temperatures have been experienced.
Brake system capacities vary on differing vehicles. Typically 2 Pints (or approximately 1 Liter) should be sufficient to completely flush the old fluid and replace with new. We recommend 4 Pints or 2 Liters of Fluid to be certain that your system is completely flushed of old fluid- and this also allows for some extra fluid to spare.
