3 Brake Fluid Types: Detailed Facts

This article discusses about brake fluid types. The braking fluid is used as hydraulic fluid inside the braking system of vehicles.

Hydraulic force is applied with the help of hydraulic fluid. The fluid uses Pascal’s law for transferring the force from one end to other. We shall see more about types of braking fluid, mechanism of braking system and other related topics.

• DOT 3
• DOT 4
• DOT 5
• DOT 5.1

What is braking fluid?

The type of hydraulic fluid that is used in braking systems and clutches of automobiles.

Generally the braking force applied to the braking pedal is very less than the actual force needed to stop the vehicle in motion. The braking fluid converts this force into pressure and amplifies it enough that the resulting amplified force can stop the vehicle.

Image credits: anonymous, Disc brake, CC BY-SA 3.0

Define brake fluid types

Brake fluids are of four types. The designation of these brake fluids start with DOT that means Department of Transportation. The four types are-

DOT 3

DOT 3 is a glycol based braking fluid. The term is a standard term used in US. DOT 3 is equivalent to SAE J1703.

DOT 4

DOT 4 is also a glycol based braking fluid generally used as a temperature upgrade for DOT 3. Most cars after 2006 used DOT 4 brake fluid as their standard braking fluid.

DOT 5

A braking fluid that is silicone based and also it is completely different from the series of DOT (2,3,4,5.1) It does not mix with water and other brake fluids. It is recommended that this braking fluid should not be mixed with other braking fluids.The biggest advanatage of silicone over other materials is that silicone based fluid has more stable viscosity index with working conditions having a wide variety of temperature values.

DOT 5.1

Although, DOT 5 was a better version among other DOT versions. Lack of its acceptance led rise to DOT 5.1 which is again a glycol based braking fluid. It gives functioning similarities with silicone based braking fluid and can be termed as non silicone version of DOT 5. That is a version having similar properties of DOT 5 while using Glycol ether based raw materials.

Brake fluid properties

The braking fluid undergoes extreme conditions as the vehicle runs sometimes on smoother road and sometimes on rough and bumpy road. The weather may be hot sometimes, rainy sometimes and sometimes cold.

According to these conditions the braking fluid cannot be changed every now and then. So it has to have properties such that it can bear extreme situations. The ideal properties for a braking fluid are-

• High breaking point- As the vehicle experiences immense heating during its operation, it is recommended to have a braking fluid which can operate at high temperatures.
• Good low temperature properties– Sometimes the temperatures are below normal levels during cold, at this time the braking fluid may solidify if it does not have good low temperature properties.
• Good viscous properties- The braking fluid should have an optimum amount of viscosity. It should not be loose and also not thick that it does not move easily.
• Anti corrosive properties– The braking fluid should have anti corrosive properties otherwise it will corrode the material used in braking lines damaging the entire braking system.
• Physical stability– A good braking fluid has good physical stability that means it should not get distorted or change its phase once it is subjected to huge amount of force and pressure.
• Chemical stability- A good braking fluid does not mix with other liquids, it should have good chemical stability. It should maintain its chemical structure and should not be easily contaminated by outside impurities.
• Compressibility- The entire functionality of braking fluid depends on its compressibility. If the compressibility is not good then it won’t be able to provide required pressure and so the braking system will fail which in turn means that the vehicle won’t be stopped.

Bike brake fluid types

Bikes usually use two types of braking fluids. These fluids are discussed in detail below-

• DOT fluid- Above section discusses about DOT fluids in detail. They are mostly made of Glycol Ether based materials and generally each higher version has a better working temperature range. Except for DOT 5 which is a silicone based braking fluid and that has better properties than DOT 2, DOT 3 and DOT 4.
• Mineral oils– This is the normal mineral oil that we purchase from grocery stores. This is generally meant for lighter vehicles such as two wheeler.

DOT brake fluid types

As discussed in the sections above, DOT brake fluids are classified into many types. Typical basis of classification is the working properties and the raw materials used while making the braking fluid.

The types of DOT braking fluid are-

• DOT 2– Has a low working range of temperature.
• DOT 3– Has a greater working temperature range than DOT 2.
• DOT 4- Has even greater working temperature range than DOT 2 and DOT 3.
• DOT 5- This is made up of silicone based materials and has better properties.
• DOT 5.1– Although made of Glycol Ether based materials, it has similar properties as that of DOT 5.

Car brake fluid types

In cars usually glycol ether based brake fluids and silicone based brake fluids are used. These fluids are discussed in above sections. Most commonly used braking fluids in cars are DOT brake fluids. More specifically, following DOT brake fluids are used-

• DOT 3- As discussed above it is a Glycol Ether based braking fluid that is used in lighter vehicles. This braking fluid can be used in hatchback cars that are light in weight. It has a smaller range of working temperature.
• DOT 4- As discussed above, it is also a Glycol Ether based braking fluid that is used for comparatively heavier vehicles such as SUVs. This braking fluid has a greater working temperature range.

Auto brake fluid types

In autos, usually DOT 3 type of braking fluid is used. As an auto is considered in lighter weight vehicle type, it does not need higher versions of braking fluid like DOT 4 and 5. DOT 3 is sufficient for autos.