What is Brake Fluids: Types, Benefits and Signs of Low Brake Fluids

The braking system is one of the essential components of a vehicle, which requires a myriad way of maintenance. Hence, car owners need to be more careful about their well-being and carry on the necessary chores like changing different oils to eliminate the chances of a breakdown. One of the important components of a brake is brake fluids or hydraulic fluid. 

In this context, the importance and usage of brake fluids have been mentioned to offer complete knowledge to car owners.

Brake fluid or hydraulic fluid is a vital part of the hydraulic braking system, which is used by drivers on every occasion they use brakes to stop the car. Without the presence of sufficient brake fluids, the car brakes will not be able to function properly. 

This liquid chemical solution is a must-have for modern cars and must be present at constant viscosity, even during temperature fluctuations. Regular brake fluids are available as glycol – or silicon-based. 

Hence, due to its variety, it is important to ascertain the right brake fluid type for the car, which is available in the owner's manual and use the same.

To answer “what brake fluid does”, this solution plays a crucial role in the functioning of a vehicle's braking system. It is a hydraulic fluid specifically designed to transmit the force applied on the brake pedal to the actual brake components, enabling the vehicle to slow down or stop effectively. 

Here's what brake fluid does and how it functions in the braking system:

Transmitting Force

When you press the brake pedal, it creates hydraulic pressure in the master cylinder of the braking system. This pressure is then transmitted through the brake lines filled with brake fluid.

Multiplying Force

Brake fluid is an incompressible fluid, which means it doesn't easily compress when pressure is applied to it. This property allows the hydraulic force to multiply as it travels through the brake lines. As a result, the relatively small force exerted on the brake pedal can generate much greater force on the brakes themselves.

Actuating the Brakes

The pressurised brake fluid reaches the brake callipers or wheel cylinders in the braking system, depending on the type of brake system (disc brakes or drum brakes). In disc brakes, the fluid applies pressure on pistons within the callipers, causing the brake pads to clamp down on the brake rotor, creating friction and slowing down the vehicle. In drum brakes, the fluid forces the brake shoes outward against the brake drum, generating friction to stop the vehicle.

Heat Dissipation

During braking, a significant amount of heat is generated due to friction between the brake components. Brake fluid is designed to have a high boiling point to withstand these elevated temperatures and prevent the formation of vapour bubbles, which can lead to brake fade or a loss of braking efficiency.

Corrosion Prevention

Brake fluid is formulated to protect the metal components within the braking system from corrosion and rust, ensuring the smooth and reliable operation of the brakes over time.

It is crucial to maintain the proper level and quality of brake fluid in your vehicle. Brake fluid can absorb moisture over time, which can reduce its effectiveness and potentially lead to brake system failure. 

Therefore, regular brake fluid checks and flushes, as recommended by the vehicle manufacturer, are essential for safe and reliable braking performance.

The frequency at which brakes need to be changed can vary depending on several factors, including the type of brake system, driving habits, and environmental conditions. Here are some general guidelines for when to change brakes:

Brake Pads

Brake pads are the most common brake component that requires replacement. They typically have a lifespan of about 30,000 to 70,000 miles (48,000 to 113,000 kilometres), but this can vary based on the type of brake pads (e.g., organic, semi-metallic, ceramic) and driving conditions. Performance-oriented brake pads may have a shorter lifespan, while high-quality ceramic pads might last longer.

Brake Rotors

Brake rotors, also known as brake discs, may last longer than brake pads, usually between 50,000 to 70,000 miles (80,000 to 113,000 kilometres) or more. However, their lifespan can be affected by factors such as aggressive driving, heavy loads, and frequent braking.

Drum Brakes

If your vehicle is equipped with drum brakes on the rear wheels, the brake shoes inside the drums will require replacement at some point. Drum brakes tend to last longer than disc brakes, and their replacement interval can vary widely, from 50,000 to 100,000 miles (80,000 to 160,000 kilometres) or more.

Regular maintenance and inspections by a qualified mechanic are essential to ensure the braking system's safety and reliability. They can assess the condition of the brakes and provide recommendations for replacement based on the wear level and the vehicle's specific requirements. 

Always follow the maintenance schedule provided by your vehicle's manufacturer to keep your brakes in good working condition and ensure your safety on the road.

Low brake fluid can lead to compromised brake performance, which is extremely dangerous for the safety of the vehicle and its occupants. Here are some signs that your brake fluid might be low:

Illuminated Brake Warning Light

Nowadays, vehicles have a dashboard warning light that indicates a problem with the brake system. If your brake fluid is low, this light may come on. It can vary depending on the car model, but it's usually a red or yellow exclamation mark inside a circle.

Soft or Spongy Brake Pedal

If you notice that your brake pedal feels soft and spongy or goes closer to the floor than usual before engaging the brakes, it could indicate a low brake fluid level. The brake fluid is essential for creating hydraulic pressure, and when it's low, it may lead to a decreased braking response.

The Brake Pedal Takes More Effort to Engage

If you have to press the brake pedal with more force than usual to make the brakes work, it could be a sign of low brake fluid. The lack of sufficient fluid can result in reduced hydraulic pressure, making the brakes less effective.

Visible Fluid Leaks

Check around the wheels and under the car for any signs of fluid leaks. Brake fluid is typically clear or slightly yellowish, and if you see any puddles or drips, it could indicate a leak in the brake system, leading to low fluid levels.

Brake Fluid Reservoir Level

Most cars have a transparent brake fluid reservoir under the hood, near the firewall. You can check the fluid level visually. If the level is below the "MIN" or "LOW" mark, it's a clear sign that your brake fluid is low.

Squealing or Grinding Noise when Braking

While this can be a sign of worn brake pads, it can also indicate low brake fluid. If the fluid is low, the brake callipers may not fully engage the brake pads with the rotors, causing them to vibrate and produce unusual noises.

Brake System Warning Message

In some vehicles, along with the brake warning light, you may also receive a warning message on the dashboard indicating low brake fluid.

Driving with low brake fluid can put you and others on the road at risk, as it may result in poor braking performance or complete brake failure. If you're unsure about how to check or add brake fluid, it's best to consult your vehicle's owner's manual or take your car to a qualified mechanic for inspection and proper maintenance.

The most common types of brake fluids include:

DOT 3

DOT 3 brake fluid is one of the earliest types and is glycol-based. It is a standard brake fluid suitable for most vehicles and has a boiling point of around 205°C (401°F). However, it tends to absorb moisture over time, leading to a decrease in boiling point and potential brake system corrosion. It is suitable for most conventional braking systems.

DOT 4

Similar to DOT 3, DOT 4 brake fluid is also glycol-based but has a higher boiling point, typically around 230°C (446°F). It offers better performance under heavy braking and is more resistant to moisture absorption. This DOT 4-wheel oil is also compatible with most convent ional braking systems.

DOT 5

DOT 5 brake fluid is silicone-based, which makes it less hygroscopic (meaning it doesn't absorb moisture as much). It has a higher boiling point, usually above 260°C (500°F). This type of brake fluid is often used in high-performance and military vehicles. 

However, it's not compatible with most conventional braking systems due to its silicone nature, and it can cause damage if mixed with glycol-based brake fluids.

DOT 5.1

DOT 5.1 brake fluid is glycol-based like DOT 3 and DOT 4 but offers higher performance characteristics. It has a boiling point similar to DOT 4, around 230°C (446°F), and better resistance to moisture absorption. DOT 5.1 is also compatible with most conventional braking systems.

It's essential to use the brake fluid recommended by the vehicle manufacturer, as using the wrong type can lead to brake system malfunctions and compromise safety. Always consult your vehicle's owner's manual or a qualified mechanic to determine the appropriate brake fluid for your specific vehicle. 

Also, ensure that the brake fluid is replaced at the recommended intervals to maintain optimal braking performance.

The colour of the brake fluid acts as a clear indicator of whether the oil is in good condition or not. Hence, drivers can consider brake fluids to be up to the mark if it has an almost clear colour with a small part of yellow tint in them. 

However, when this colour changes into dark brown or black colour, this specifies the replacement of its fluid. Hence, brake fluids tend to change colour and become darker because of obtaining debris and dirt in the system due to continuous driving. 

The effectiveness of motor vehicle brake fluids and their right requirement has been offered by the Federal Motor Vehicle Safety Standards (FMVSS) No. 116. The efficacy of brake fluids and to determine its DOT classification, this chemical solution may undergo the following tests: 

• Kinematic viscosities

• pH value

• Equilibrium reflux boiling point (dry boiling point) 

• Corrosion 

• Fluid colour 

• Water tolerance (low temperature and at 60 degrees C) 

• Wet equilibrium reflux boiling point (tested with 3.7 percent water)

• Stroking properties

• Resistance to oxidation

• Fluidity and appearance at low temperature

• Compatibility (low temperature and at 60 degrees C)

• Resistance to oxidation

• Reserved

• Brake fluid stability (high-temperature and chemical stability)

It is important to consider the type of your vehicle system before purchasing brake fluids. Vehicles that have an anti-braking system (ABS) will work within a specified classification's viscosity range. 

In addition, experts recommend not mixing brake fluids, even if all fluids meet the basic DOT specifications and compatibility. Follow all the guidelines while changing your brake fluids, which will ensure a reliable braking system.