The fluid in the system absorbs water through the breathers, through the caliper piston seals and by magic. A minute amount of water suspended in the fluid decreases the boiling point as much as 1/3. Since water boils at 212 degrees Fahrenheit (100 degrees Celsius) the adsorbed water dramatically lowers the boiling point of the brake fluid. DOT 3 DOT 4, and DOT 5.1 brake fluids are ether based and, as such they are hygroscopic in nature - i.e. As a point of interest, even though they may have the same DOT rating, racing fluids are less compressible than street fluids, especially after they have been overheated.įor high performance street car use, the wet boiling point is at least as important as the dry. This is the rating by which most high performance drivers and all racers select their brake fluid – from the standard racing 550 degrees Fahrenheit to the 600+ degrees Fahrenheit offered by the extreme use fluids. They are also classified by US Department of Transportation (DOT) rating, DOT 3, DOT 4, DOT 5, and DOT 5.1.Īs we would expect the dry boiling point is just that - the temperature at which a given brake fluid boil when it is fresh out of the can. Brake fluids are classified by both “dry boiling point” and “wet boiling point”. This leads to a discussion of boiling points. Some of the reputable racing fluids include:įinally, Castrol SRF is a racing brake fluid that is in a class by itself with patented chemistry and is, in my opinion, the best racing brake fluid on the market today. The fifth is easy and relatively cheap.įor most of us easing up on the brake usage is not an option and increasing cooling air to the system is filed under too difficult so we upgrade the fluid. The third is really expensive in its various forms. Change to a brake fluid with a higher boiling point. Install Titanium pad backing plate if they are available for your caliper.ĥ. (Note that aluminum pistons are used as opposed to stainless steel to match the expansion rate of the piston to that of the caliper body to ensure the piston seal condition and preload is optimal through out the temperature range.)Ĥ. Alternately install 2-piece pistons made from aluminum with a noise piece of Titanium or Ceramic. Install Titanium or Ceramic caliper pistons. Provide (copious) cooling air to the brakesģ. There are four possible solutions to the boiling fluid problem:Ģ. In extreme cases overheated brake fluid necessitates “pumping the brake pedal” in order to get a pedal at all. Gas is compressible so boiling brake fluid leads to a “soft” brake pedal with long travel. Boiling produces gas bubbles within any boiling fluid. Overheated brake fluid can (and will) boil in the caliper. When fresh, all brake fluids are virtually incompressible and the system works as well as its mechanical and hydraulic design allows. The foot pressure is multiplied by the mechanical pedal ratio and the hydraulic ratio of the master cylinders, booster (if used) and caliper piston(s). The function of brake fluid is to provide an incompressible medium to transmit the driver’s foot pressure on the brake pedal through the master cylinder(s) to the calipers in order to clamp the friction material against the discs. Virtually no one (including me) ever changes the brake fluid in their street car - or even bleeds the brakes. Most high performance drivers check their tire pressures and change their engine oil at frequent intervals. of scR motorsportsīrake fluid is possibly the single most neglected component of the automobile.
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