BRAKE FLUIDS

•Brake fluid plays a crucial role as it transfers the force created when a driver presses the brake pedal directly onto the wheel hub.
•Heat generated under braking, especially under heavier breaking or prolonged breaking, may affect the brake fluid which can only work if it is liquid and not so hot that it has become vapour.
•Therefore the boiling point your brake fluid achieves is critical to efficient braking as temperatures above the boiling point form vapour bubbles in the system, potentially resulting in brake failure.
•In addition, the brake fluid serves as a lubricant of all movable parts and prevents corrosion. It has to be compatible with rubber seals and hoses thus allowing braking systems to achieve long service and optimal performance

what are the basic characteristics of brake fluid?
•1. Oil point: Due to high temperature during the braking applications brake Fluid should have high boiling point, to avoid vapour formation. Boiling point should be generally around 25O-3OOC.
•2. Viscosity: Due to variations in weather conditions from very cold to hot it becomes imperative that the viscosity of the brake fluid should vary little with temperature to keep optimum flow conditions. So viscosity should be such that, flow occur in pipes easily without any temperature variations.
•3. Lubrications properties : Brake fluid should have good lubrication properties so that proper lubrications of braking components (e.g. master cylinder) is done

PROPERTIES OF BRAKE FLUID
1) Thin viscosity, even at lower temperatures (they are tested at -40oC)
2) Must be compatible with the seals in the braking system
3) Reasonably non-compressible
4) High boiling point
5) Good at not absorbing water
6) A good lubricant of moving parts
7) Long-lasting
To achieve these properties, modern brake fluids are made of glycol ethers and borate esters, mixed with various corrosion inhibitors. They are completely unlike any oil used in engines.

Brake fluid types
Two types of braking fluids are used in braking applications
•Polyglycol: is close to amber in its color and the most commonly used braking fluid used in the industry.It is a solvent and will immediately begin to dissolve the paint when just reaching it. From its main disadvantages that it has a high ability to absorb water directly. Water can be absorbed through the hoses and the seals and enters the master cylinder reservoir cap, moisture in the hydraulic circuit reduces the boiling point of the braking fluid and causes it to evaporate. In addition the moisture causes metal parts to erode and rust causing the leakage or frozen wheel cylinder pistons.
•Silicone: is purple in color, it’s not hygroscopic (don`t attract water) and therefore don`t have rust or corrosion problems.

•DOT3
This is the normal specification for many of the cars on the road today, with boiling points in the region of 200oC (dry) and 140oC (wet). This type of fluid should be changed in accordance with the manufacturer’s guidelines
•DOT4
This is also a common specification for road cars, but with higher boiling points than theDOT3 fluids (230-270oC dry, 160-170oC wet) where brakes are likely to generate more heat,
For example, performance road cars. As with the DOT3 fluids, these ones are glycol based.
•DOT5
These are not relevant to road use. They are silicon based, unlike the other brake fluids listed and are hydrophobic, so they do not absorb water and are therefore extremely long life fluids. These fluids are not suitable for the vast majority of the vehicles in use today, but are for certain military vehicle purposes, as well as a few other non-mainstream applications.
The boiling points for DOT5 fluids are approximately 260oC dry and 180oc wet. The 'wet ‘boiling point is slightly different to normal brake fluids as water cannot enter the fluid, it can only be a 'wet' fluid if there is water in the braking system.
•DOT5.1
This is another glycol (unlike the DOT5 fluids) based fluid that is used in normal road and performance cars. Due to the formulation of the fluid, it is longer lasting than the DOT3 andDOT4 fluid, although the boiling points may not be much higher than the DOT4 fluids at around 270-280oC dry and 185oC wet. Do not confuse these fluids with the much rarer DOT5ones.
•Super DOT4
These are the top performance brake fluids available. They are like a DOT4 in terms of the chemical components used and life span of the fluid, but they are formulated to give extremely high boiling points (generally in excess of 300oC dry and 190oC wet). These are
The fluids that are used in the top levels of motorsport, but are still suitable for road use, so they are ideal for vehicles used on road and track