Did You Know?: Brake Fluid

Your vehicle’s brake fluid is a vital component in your braking system, creating a mechanical connection between your foot and the wheels. The physics of fluid dynamics, along with anti-lock brake technology, provide you with almost effortless control while braking. However, did you know this fluid needs service periodically? In this article, we’ll explore the reason why you should have Brandon Honda’s Brake Fluid Exchange Service performed every three years as recommended by American Honda.


What makes brake fluid a mechanical connection is its property as a fluid when dry, meaning no moisture contamination. When dry, brake fluid is incompressible, allowing it to act as a mechanical connection between the master cylinder and the wheel components, the calipers and wheel cylinders. This is the ideal state for brake fluid. As stated in an article on StopTech.com, “By definition, DOT 3 fluids must have a minimum dry boiling point (measured with 0 percent water by volume) of 401°F and a minimum wet boiling point (measured with 3.7 percent water by volume) of 284°F.”


Another property of brake fluid is that it is hygroscopic. This means it has the ability to absorb moisture. As you can see in the above statistic, brake fluid with only 3.7% moisture by volume drops in boiling temperature almost 120 degrees. This is significant because in my 30 years of experience I have had on occasion to measure brake temperatures. On a typical road test with normal braking, I have measured temperatures of 200 degrees right after stopping. On brakes with a malfunction such as a caliper piston that is not retracting, I have seen temperatures of 500 degrees and higher. This is a potentially dangerous condition that can be detrimental to the stopping power of your vehicle.


In spite of the fact that the brake master cylinder on your vehicle contains rubber seals to keep out contaminants, moisture can still leech through over time. Brake fluid with moisture content decreases the natural incompressibility of the fluid, softening the pedal feel for the driver, who now has to exert more effort in stopping their vehicle. In addition to keeping your braking system working optimally, flushing your system of old, moisture-laden fluid also reduces the possibility of corrosion developing internally, potentially saving you thousands of dollars in repairs.


American Honda, as noted in the training course each of our certified technicians is required to pass to work on your Honda, recommends servicing the brake fluid through an exchange process EVERY 3 YEARS, regardless of mileage. Visit our scheduler to obtain an appointment today, or if you have any other questions for one of our technicians, visit us at Ask A Tech on our website.

December 3, 2020
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