Brake fluid is a critical component of the hydraulic braking system. It transmits the force exerted on the brake lever to the pistons of the calipers and also has the function of preventing the formation of water drops in the circuit to prevent corrosion of the components.
Because of its importance to user safety, the United States Department of Transportation (DOT) required brake fluid manufacturers to meet certain safety requirements when to make them. From these requirements arose the DOT indices (DOT 3, DOT 4, DOT 5 and DOT 5.1), all of them aimed at specifying the composition of liquids according to their dry boiling point, their wet boiling point, their viscosity and the base of the liquid. liquid, normally derived from polyglycol but also with silicone bases and even mineral oils:
- DOT 3: glycol-based, used in conventional brakes. It has a dry boiling point of 205ºC, humid 140ºC and a viscosity of 1500cSt. It can be mixed with DOT 4 and DOT 5.1 liquids, although it is not recommended.
- DOT 4: glycol-based, used in ABS and conventional brakes. It has a dry boiling point of 230ºC, humid of 155ºC and a viscosity of 1800cSt. It can be mixed with DOT 3 and DOT 5.1 liquids, although it is not recommended.
- DOT 5: silicone-based, used in high-performance brakes without ABS. It has a dry boiling point of 260ºC, wet of 185ºC and a viscosity of 900cSt. It cannot be mixed with DOT 3, DOT 4 and DOT 5.1 liquids.
- DOT 5.1: glycol-based, used in high-performance brakes with or without ABS. It has a dry boiling point of 260ºC, wet of 180ºC and a viscosity of 900cSt. It can be mixed with DOT 3 and DOT 4 liquids, although it is not recommended.
How to choose one or the other type?
We must start from the basis that a braking system generates a lot of heat, so the boiling point of brake fluid (the higher the better) is a factor to take into account.
Another important fact is that glycol-based liquids (DOT 4, DOT 5 and DOT 5.1) are hygroscopic (they absorb moisture) and, therefore, tend to deteriorate over time and should be changed every 2 or 3 years. , while silicone-based liquids (DOT 5) are hydrophobic (they repel moisture), so they withstand the passage of time better and do not deteriorate the rubber gaskets.
To know the state of the brake fluid, we can use amoisture testerspecific for brakes.
In any case, the brake manufacturer specifies the type of brake fluid to be used in your product, so the best brake fluid will always be the one recommended by the manufacturer of the motorcycle or the braking system.
Frank burguera
#mecanicaharley