What is brake fluid?

Created by Jonathan Fry, Modified on Thu, 27 Mar at 4:03 PM by Jonathan Fry

Brake fluid is a specialised hydraulic fluid used in the brake systems of vehicles, playing a vital role in ensuring safe and effective braking. This fluid operates under high pressure to transmit force from the brake pedal, allowing the driver to slow down or stop the vehicle efficiently. Here are several detailed aspects of brake fluid that are important to understand:

Function

The primary function of brake fluid is to transfer hydraulic pressure from the brake pedal to the brake components. When the driver presses the brake pedal, the fluid is forced into the brake lines, which then activates the brake callipers or wheel cylinders. This action applies pressure to the brake pads or shoes, creating friction against the brake discs or drums, ultimately slowing or stopping the vehicle. Because of this hydraulic mechanism, the fluid must be incompressible to ensure effective braking response.

Types of Brake Fluids

Brake fluids are categorised by their chemical composition and performance standards set by the US Department of Transportation. The most common types include:

DOT 3: A glycol-ether based fluid with a lower boiling point, suitable for most standard vehicles. It absorbs moisture over time, which can lead to a decrease in performance if not replaced regularly.
DOT 4: A higher performance fluid that has a higher boiling point than DOT 3, making it suitable for vehicles that experience heavier braking loads, such as sports cars or vehicles used for towing.
DOT 5: This is a silicone-based fluid that does not absorb moisture, thus providing excellent protection against corrosion. However, it's not compatible with other types of brake fluid, making it essential to ensure system compatibility before use.
DOT 5.1: Similar in performance to DOT 4 but with a higher boiling point, DOT 5.1 is glycol-based and can be used in both standard and high-performance applications.

Properties

In addition to having a high boiling point, which is crucial to prevent vaporization and brake failure during intense use, brake fluid is designed to remain stable across a wide range of temperatures. Important properties of brake fluid include:

Non-compressibility: Ensures that the force applied at the brake pedal is effectively transmitted to the brake components without any delay or loss of power.
Corrosion resistance: Brake fluid needs to protect metal components within the brake system from corrosion and wear, extending the lifespan of these parts.
Lubrication: It must also provide some level of lubrication to moving parts within the brake system to reduce friction and wear.

Maintenance

Regular maintenance of brake fluid is essential for the safe operation of the vehicle. Over time, brake fluid can absorb moisture from the air, which can lead to several issues:

Reduced boiling point: This can cause the fluid to boil during heavy braking, resulting in a phenomenon known as "brake fade," where the brakes become less effective.
Corrosion: Moisture can lead to the corrosion of metal components within the brake system, such as calipers and brake lines, potentially leading to costly repairs.
Contamination: Brake fluid can also become contaminated by debris or other substances, which can further compromise braking efficiency.

To maintain optimal performance, it is advisable to check the brake fluid level and quality regularly. Most manufacturers recommend replacing the brake fluid every 1 to 2 years, depending on the vehicle's usage and the type of fluid used.

Conclusion

In summary, brake fluid is a crucial component in the safe operation of any vehicle. Understanding its function, types, properties, and maintenance needs is essential for vehicle owners to ensure their braking systems function efficiently and safely. Proper care and timely replacement of brake fluid not only enhance performance but also contribute to the longevity of the braking system as a whole.