In this REMSA blog we cannot overlook brake fluid, as there are many drivers who do not give importance to this element, which is a key element for a correct braking action.
Brake fluid is a hydraulic fluid that enables the transmission of the force exerted on the brake pedal to the brake cylinders on the wheels of the different vehicles.
Therefore, it is the element that, when pressurized by the pump, pushes the calliper cylinders against the pads, thus producing the braking action.
A brake fluid in good condition ensures proper braking, but it is an element that degrades with use and the passage of time and must be replaced when this occurs.
Fundamental characteristics of brake fluid
- It is incompressible (like all fluids).
- Its minimum boiling point must be higher than 230ºC. In this way, it will remain liquid, without boiling, when braking is very demanding.
- It must have low viscosity to move quickly through the circuit.
- It must be a lubricant so that the moving parts of the braking system with which it is in contact do not seize.
- It must be chemically stable, so as not to corrode the elements of the braking system with which it is in contact.
Today, most brake fluids satisfy all the requirements demanded of them. However, its replacement is necessary every two years or 70,000 km since, due to the composition of its elements, it possesses a property that makes this change necessary. We are talking about the hygroscopic property, that is, it has a great capacity to absorb water. Accordingly, in humid environments, it may be necessary to replace the brake fluid before the foregoing deadlines.
Why is the hygroscopic capacity of brake fluid negative?
We might think that if there were water in the braking system it would not modify the qualities of the fluid, since it is also a fluid. But this is not the case since water, even in its liquid state, corrodes the elements of the brake system with which it is in contact.
The main problem with water in the braking system is that when the temperature of the liquid exceeds 100ºC the water evaporates and transforms into steam, a gas, which is compressible, so the pedal would go all the way to the bottom. Why? Because all the pressure exerted in the system will serve to compress that steam vapor and not to act on the brake pads. In addition, the existence of water in the system lowers the boiling point of the liquid.
Types of brake fluids
Brake fluids are currently divided into two groups depending on their features. Thus, two grades of brake fluid are sold.
A. DOT 4: Its boiling point is 255ºC. Used in disc/drum or disc/disc systems without ABS. It is one of the products that we make available to our customers and distributors at REMSA.
B. DOT 5: Its boiling point is 270°C. It must be the one used for high performance vehicles and those equipped with ABS systems.
Both liquid qualities are miscible with each other (they can be mixed in any ratio), but mixing the two is not recommended. Although there is the possibility of mixing them, it is advisable to read the vehicle’s maintenance handbook to know, if we need to refill, what type of fluid our vehicle uses.
So when we replace the brake fluid it is appropriate to clean the circuit with methyl alcohol to ensure that the new fluid retains all its properties. In addition, the braking system must be bled after any manipulation.
Lastly, it should be remembered that vehicles with air suspension use the same fluid as brake fluid. This type of fluid is called LHM and it is very important to note that DOT type brake fluid mixed with LHM should not be used, as this will damage the entire system.
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