Brake fluid

Brake fluid is the fluid that allows the force exerted from the brake pedal to be transmitted to the caliper piston, thus allowing effective braking.

Brake fluid must be kept in good condition and to do so it is necessary to change it periodically.

In this sense, one of the main factors that must be checked is the boiling point, since the more heat generated and the higher the temperature reached by the brake fluid, the easier it will be for it to boil, and if this happens, bubbles appear that reduce the effectiveness of braking.

Another factor that most affects brake fluids is that they have hygroscopic properties , meaning they are prone to absorbing water from ambient humidity. For this reason, it is recommended to change them every 2 years or 60,000 kilometers, depending on their condition.

Types of brake fluids.

Another point to keep in mind is that you should always use the brake fluid appropriate for each vehicle and each type of competition.

Using the wrong, expired or dirty brake fluid can cause serious damage to the system, so it is recommended to drain all the fluid, flush the system and refill it with the correct fluid.

Now, what types of fluids exist and what types of brakes should they be used in?

• DOT 3 : Used in conventional brakes. It has a dry boiling point of 205ºC, a wet boiling point of 140ºC and a viscosity of 1500 cSt (viscosity units) . It is also very hygroscopic, absorbing about 2% of its volume of water per year. Its composition is very strong and should not be used from open containers. It is the most common and cheapest.
• DOT 4 : This is known as LMA (low moisture absorption) or low moisture absorption fluid. It is a liquid used in both conventional brakes and ABS. It has a dry boiling point of 230ºC , a wet boiling point of 155ºC and a viscosity of 1800cSt. It is similar to DOT 3 although it offers better performance and greater durability. Within this type we can also find the Super Blue Racing specification , which offers much higher performance and has a boiling point of 260ºC.
• DOT 5 : DOT 5 is a non-hygroscopic fluid made of silicone (polymethyl siloxanes). It cannot be used in vehicles with synthetic-based brake fluid. It absorbs a large amount of air (three times more than DOT 3 and DOT 4 types), especially at high altitudes. This makes bleeding difficult, as the trapped air expands as the temperature increases. It must not be mixed with any other type of brake fluid. Its boiling point is 260ºC.
• DOT 5.1 : It is a synthetic liquid with a dry boiling point of 270ºC, a wet boiling point of 180ºC and a viscosity of 900cSt. Contrary to what one might think, it is not an evolution of DOT 5, but of DOT 4. Its main disadvantage, like DOT 3 and DOT 4, is that it is hygroscopic, that is, it has a great capacity to absorb moisture.