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BRAKE FLUID
Q. What is the role of brake fluid?
A. Automobiles use fluid (hydraulic) brakes.
When the driver steps on the brake pedal, a piston in the master cylinder is pushed, generating hydraulic pressure, which transmits amplified force to each disc brake caliper. The brake pads are then pressed against the brake discs that are linked to the wheels, and the friction generated there applies the brakes.
Within this braking system, the liquid that generates hydraulic pressure and transmits force smoothly is called brake fluid.
Q. What are the characteristics of brake fluid?
A. Brake fluid has low viscosity, small volume change due to pressure, and does not freeze at low temperatures of -50°C or boil at high temperatures of 200°C. It has the characteristics of being able to withstand various environmental changes.
If the fluid cannot maintain its performance, it cannot be used as brake fluid.
Q. What types of brake fluid are there?
A. There are three types based on the ingredients. Glycol-based brake fluids are the most common because of their excellent brake fluid properties, but there are also silicone-based and mineral oil-based types.
There are also types based on specifications according to DOT and JIS standards.
Q. What is glycol brake fluid?
A. TThe main ingredient is polyethylene glycol monoether, to which antioxidants and rust inhibitors have been added.
Glycol-based brake fluids absorb water and do not allow free water to exist. If free water is present, it will boil at 100°C and cause vapor lock. In winter, the water will freeze and damage parts. If it absorbs moisture, the boiling point will not reach 100°C, but it will drop slightly.
High-grade DOT4 and DOT5.1 brake fluids use borate esters of polyethylene glycol monoether, which allows them to maintain a relatively high boiling point even when they absorb moisture.
Racing vehicles, which use heavy brakes, require brake fluids with a high boiling point, low viscosity, and good responsiveness.
Q. What is silicone brake fluid?
A. It is a brake fluid whose main component is dimethylpolysiloxane, and is only used in brake systems designated as silicone-based, such as some racing cars.
It has the advantage of not absorbing moisture and not damaging paint, but it also has the disadvantage of being easily affected by rubber such as brake system seals.
Also, if water gets mixed in, it will not dissolve and will remain as droplets, which can cause the droplets to boil or freeze.
If mixed with glycol-based fluids, they will separate, so they cannot be mixed.
Q. What is mineral oil-based brake fluid?
A. It is a brake fluid whose main ingredient is mineral oil derived from petroleum. It is also called mineral-based or mineral oil-based.
Mineral oil is used in Citroën vehicles equipped with hydropneumatic systems, as the oil is shared by the suspension, steering, and brakes. If mixed with glycol-based fluids, they will separate, so they cannot be used together.
