While we have discussed most major components of an auto brake system to date, one other important element is brake fluid. This component is, in effect, the ‘lifeblood’ of a braking system since nothing moves without it.
Auto brake systems are driven by hydraulics, or in more formal terms; ‘the use of a non-compressive liquid in order to generate control, thereby transmitting mechanical power as necessary’. We’ll get into details relating to the specifics of ‘hydraulics’ in another primer, but for the time-being, lets just say that when a driver pushes the pedal down, the brakes stop the car.
Nevertheless, there’s still a lot of fluid moving in ‘the veins’ of a brake system as it were, in order to ensure that everything works properly. So, let’s get into the weeds a bit, and see what is and isn’t important when it comes to this chemically slick liquid.
What is brake fluid?
How does brake fluid help your vehicle? Brake fluid is used as a hydraulic element necessary to drive calipers pistons on- demand. These pistons, in turn, drive brake pads against a brake rotor. This second event creates friction that stops a brake rotor from turning.
What types of vehicles use brake fluid? – All hydraulic brake systems, in all vehicles, utilize one of three primary Department of Transportation (DOT) viscosities identified as DOT 3, 4, and 5. There is a sub-set identified as DOT 5.1 but are largely specific to more exotic blends and not typically relevant to performance or race purposes.
Can you mix different types of brake fluid? – As the old saying goes; ‘just because you can do a thing, it doesn’t necessarily mean you should’. Along with types of suggested viscosities, DOT fluids also harbor different levels of corrosion that can cause damage to brake lines and fittings if mixed.
What is ‘bleeding’ the brakes? – By design, hydraulic brake systems operate best when air is purged completely from a system. The process of ‘bleeding’, involves opening a fitting in one or more calipers, then pumping the pedal repeatedly until only fluid remains in all lines. Once the process is complete, all fittings are closed, and brake systems efficiency is typically returned.
Do I need a brake fluid flush? – Depending on the particular car, end-to-end brake ‘flushes’ are not necessary as long as the brake system is topped up with fluid regularly, and maintained properly. However, if components are replaced, or retrofitted it is suggested that a ‘flush’ is called for since there may be some clag left over in the sealed system, which should be better cleared completely.
What types of brake fluid apply to performance cars? – US Department of Transportation (DOT) compliant brake fluids are sold on, the basis of two measured operating values. The first relates to the potential of moisture absorption, and the second involves how well a brake fluid resists overheating at particular temperature ranges. Altogether these metrics are referred to as ‘viscosity’.
As one may expect, then, DOT viscosity usually relates to various vehicular types and how they are going to be utilized, ranging from consumer-only braking systems, to modified street performance cars, and finally track-only racing packages. In all cases, however, excessive moisture, and/or the potential of uncontrolled heat can trigger caliper ‘boil-over’, which in turn, can create operating problems if the wrong DOT value is utilized.
Consequently, understanding and applying the proper fluid becomes a critical element in terms of proper use and service maintenance.
Necessary DOT ranges include:
Dot 3 – Consumer grade. Suitable for daily-driver road cars, but less applicable to performance cars.
Dot 4 – This DOT value is considered to be ‘race-designed’ to offer appropriate levels of viscosity and necessary for hard braking for extended periods.
Dot 5 – This fluid value is represented by a synthetic manufacturing process, and most seen in heavy-duty military equipment. However, some vintage performance cars call for its use as well, since its corrosive characteristics do not damage paintwork resulting from the potential of fluid splash-over or leakage.