What Is Brake Fluid and Everything You Need To Know About It

When it comes to maintaining a safe and efficient car, one aspect that is often overlooked is the importance of the brake fluid in the braking system. A crucial component in bringing your vehicle to a halt safely, brake fluid plays a pivotal role in transmitting the pressure applied to the brake pedal into the actual function of slowing down your car. As such, ensuring that your brake fluid remains in optimal condition is of utmost importance.

This comprehensive guide aims to provide you with everything you need to know about brake fluid, including understanding its properties, the workings of the brake fluid reservoir, and the necessary maintenance steps to keep your car's braking system in tip-top shape. 

What Is Brake Fluid?

Brake fluid is a hydraulic fluid in your car's brake system that turns the force you apply to the brake pedal into pressure, which activates the brake pads or shoes to stop the vehicle. It's designed to keep a consistent thickness in various temperatures, ensuring the brakes work well in all conditions. It's chemically stable, corrosion-resistant, and compatible with brake system components. 

How Does Brake Fluid Work?

When pressure is applied to the brakes, a vacuum booster just behind the pad enhances that force. This boost activates the master cylinder, pushing brake fluid into the lines. The harder the brakes are pressed, the more pressurized fluid becomes, which increases the stopping force.

Brake fluid flows through the lines until it reaches each wheel's caliper or the wheel cylinder. Then, the pressurized fluid forces a set of pistons to push the brake pads against the spinning rotor. Since brake fluid is incompressible, it can act as a solid force under pressure even though it is a liquid. When the brake pads rub against the rotor, the vehicle's friction causes it to slow and eventually stop.

What Are the Types of Brake Fluid?

Brake fluid is vital for the effective and safe operation of the brakes in your vehicle.

There are several types of brake fluids, each designed for different vehicle types and requirements.

Glycol-Based Brake Fluids (DOT 3, DOT 4, DOT 5)

These fluids absorb water, preventing corrosion in the brake system and decreasing the fluid's boiling point over time. It's crucial to replace these fluids periodically to maintain their performance and prevent issues due to water absorption.

• DOT 3

  • This is a standard brake fluid, suitable for most everyday vehicles.

  • It can absorb a moderate amount of water and has a lower boiling point than DOT 4 and DOT 5.

  • This braking fluid is satisfactory for general use but has a reduced boiling threshold. It is to be noted that in the case of excessive heat generation in your vehicle's braking system, for instance, while driving through hilly terrain or carrying heavy cargo, the brake fluid has the potential to reach its boiling point. In such an event, the braking system may exhibit suboptimal performance.
    
    

• DOT 4

  • An improved version of DOT 3, with a higher boiling point and additional additives for better performance in higher temperatures and more extreme conditions. You'll often find this in sports cars or vehicles that are designed for tougher driving conditions.

Silicone-Based Brake Fluid 

• DOT 5

  • Further improvement on DOT 4, offering an even higher boiling point for vehicles subjected to higher thermal stress, such as sports cars and heavy-duty vehicles.

  • DOT 5 brake fluid is an improvement over DOT 4, offering an even higher boiling point for vehicles that are subjected to higher thermal stress, such as sports cars and heavy-duty vehicles. DOT 5 brake fluid is primarily used in vehicles with ABS brake systems.

Comparison Table

Source: The Build Journal |  Engineerine | RX Mechanic

Signs of Low Brake Fluid

It is crucial to keep an eye on brake fluid as it can be dangerous when it runs low. Here are some symptoms that may mean it’s time for replacement:

• Soft Pedal
  
  If the brake pedal feels softer than usual or sinks towards the floor without much resistance, this may represent low brake fluid. In this case, the pedal often seems squishy and requires more force from the foot. This is a clear indicator that the brake is not operating effectively and should be serviced soon.
  
  

• Oily Puddle beneath the Vehicle
  
  If there is a puddle of liquid beneath the car that is slightly oily to the touch, the brake system may be leaking. There are many places where a leak can occur, including rubber hoses, calipers, and master cylinders. If this happens, you should have a professional inspect your braking system immediately to ensure safety.
  
  

• Anti-Lock Braking System Warning Light
  
  An illuminated anti-lock braking system (ABS) warning light on a dashboard means that the brake fluid is running low and may be indicative of a leak. The ABS needs a sufficient amount of brake fluid level to work correctly, so if the warning light is on, the safest bet is to get a professional inspection.
  
  

• Old Brake Pads
  
  If the brake pad has not been serviced in a long time or is making a whining noise, it is a good idea to have them serviced and maybe even replace the brake fluid. As brake pads wear down, they become thinner and must be pushed harder for them to reach the rotor. The thinner the brake pads, the more fluid it takes to fill the calipers to properly squeeze them.
  
  

When should I replace my brake fluid?

Brake fluids should be changed following the owner’s manual recommendation or that of a qualified technician which is typically every 30,000 miles or every 2 years.

The brake system is designed to be a closed system. However, brake fluid is hygroscopic, which readily absorbs moisture from the air. It is impossible to keep small amounts of water from mixing with the brake fluid, usually due to microscopic holes in rubber hoses, imperfect sealing, or leaving the brake fluid cap open for longer periods than necessary.

Exposure to the air can increase the water content inside the brake fluid. Even a tiny amount of water contamination can cause the brakes to lose effectiveness since water decreases the brake fluid's boiling point. Excess water can also cause metal parts to corrode.

Brake fluid also needs to be changed because there may also be corrosion in the brake lines. Brake fluid has corrosion inhibitors and antioxidants that keep essential parts of the brake system working smoothly, but eventually, these inhibitors break down, leading to metal corrosion and a buildup of contaminants that disrupt the brake fluid flow.

What Kind of Brake Fluid Does Your Vehicle Need?

Use the brake fluid specified in your car's owner's manual for best performance and safety. Common types are DOT 3, DOT 4, and silicone-based. DOT 4 has a higher boiling point, providing reliable brake performance under high temperatures. Though DOT 4 can often replace DOT 3, don't mix them.

Silicone-based fluids are for specific vehicle types and shouldn't be used in modern brake systems. Always stick to the manual's recommendations to avoid potential brake system damage.

Top Brake Fluids in the Market

*Note not in a particular order

Source: The Build Journal |  Engineerine | RX Mechanic

Where can I buy Brake Fluids?

If you are looking to buy brake fluids, there are various places to purchase them. Auto parts stores such as AutoZone, O'Reilly Auto Parts, and Advance Auto Parts usually carry a selection of brake fluids.

These stores generally have knowledgeable staff who can help you select the right type of brake fluid based on your vehicle's specifications. Additionally, you can check your local Walmart or Target, as they often have automotive sections where brake fluids may be available.

Online retailers such as Amazon and eBay also offer brake fluids, and you can usually find a wide variety of brands and types to choose from. 

It's important to note that brake fluids are not interchangeable, and you must use the type recommended for your vehicle. 

1. Amazon.com

2. Walmart.com

3. AutoZone.com

4. AdvanceAutoParts.com

5. OReillyAuto.com

6. NAPAonline.com

7. SummitRacing.com

8. Jegs.com

9. SpeedwayMotors.com

Stress no more and call your trusted local mechanic to handle Brake Fluid Issues

Brake fluid is necessary to maintain the vehicle and driver safety. Routine inspections are essential to ensure that there are no mishaps that can lead to injury or even death.

At NuBrakes, we offer a free repair quote and the freedom to select your repair date. Our technicians will check your brake fluid and other essential system components and make recommendations based on what they see.

Contact us to learn more about our service options.

References

• https://www.bluestar.com/get_informed/article/the-importance-function-of-brake-fluid
• https://www.romeovilletoyota.com/stop-right-there-understanding-the-importance-of-brake-fluid/