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What Is Brake Fluid?

Jan 11, 2021 ·

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There are many different parts that contribute to the operation of the brakes in a vehicle. Because the braking system is one of the main safety features on a car, all of its parts should be maintained properly.

Many car owners know the basics when it comes to what should be maintained on their vehicles, like changing the oil on a regular basis. Something that is just as important, but might easily be forgotten, is brake fluid.

Brake fluid, also known as hydraulic fluid, is used every time a driver brings their car to a stop. Brakes are unable to function properly without this fluid – so it’s important that it’s kept in good condition.

Keep reading to find out what brake fluid does and why it’s so essential to the operation of the braking system.

What Does Brake Fluid Do?

Simply put, a car’s braking system doesn’t work without brake fluid. The brake fluid takes the force from the depressed brake pedal, translates it into pressure, and sends this pressure to the front and rear brakes to stop a vehicle.

Brake fluid can’t be compressed, which makes it perfect for use within a hydraulic braking system. It’s able to operate under the high pressure and temperatures generated when a car is coming to a stop. The role that brake fluid plays is relatively simple when broken down:

  • The driver steps on the brake pedal.
  • The linkage applies force to the piston at the master cylinder.
  • The master cylinder pressurizes the brake fluid and sends it to the wheel cylinders and calipers.
  • The hydraulic pressure acts on pistons to produce force.
  • The force is exerted on the brake pads, which make contact with the brake drum or rotor.
  • The rotation of the wheels slows or stops.

Without brake fluid, there wouldn’t be the pressure necessary to get your vehicle to a safe and complete stop. Any leaks or fluid that hasn’t been changed in a while can cause issues on the road if not addressed.

How Often Should Brake Fluid Be Changed?

You should make sure to check the condition of your brake fluid often and change it on a regular basis to ensure the braking system as a whole is able to run smoothly.

It’s easy to check the condition of brake fluid by looking – a brake fluid reservoir is under the hood and there are markings showing what the appropriate level of fluid should be. Fluid should be added if it’s at a lower level than normal and monitored in case there’s a leak.

A good rule of thumb is to check the brake fluid every time your vehicle gets an oil change. As far as completely replacing the fluid, this time frame can vary depending on the vehicle and driving conditions. Referring to an owner’s manual is the best bet to find the recommended time frame for your specific vehicle.

A student adjusts brakes in a UTI Automotive lab.

If your car runs out of brake fluid due to a leak in the system or damage to a part, the brakes are not going to work properly. It’s unsafe to drive with a low amount of brake fluid or a leak in the system.

Signs Your Brake Fluid Is Low

It’s helpful to know the signs and symptoms that might indicate your vehicle has a low amount of brake fluid. These can include:

  • The brake light coming on. The anti-lock braking system (ABS) is designed to illuminate if something within the brake system needs to be looked at. This can be a pretty obvious indicator, so be sure to check the fluid levels if you notice this.
  • Issues with your brake pedal. You might notice a few things happening with your brake pedal if your car doesn’t have a proper amount of brake fluid. It might be harder to press down on it, or the pedal might have a “soft” feel when you use it.
  • Brake pad problems. Your brake fluid works alongside parts of the braking system, including the brake pads. This means that if you hear any loud noises coming from the pads or that they’re not working properly, it could be an issue stemming from lack of brake fluid.
  • Burning smells. Any burning smells or smoke coming from your vehicle is never a good sign. This might indicate that your brakes are overheating.
  • Odd noises. A lack of brake fluid or brake fluid that is past its prime can cause there to be strange noises coming from your braking system. These can be scraping or squealing noises.

Be sure to take these symptoms seriously and ensure that you have the right amount of brake fluid in your vehicle. It might be time for a change!

Different Types of Brake Fluid

Knowing what brake fluid does and how it helps with the operation of the system as a whole is a good first step as a car owner. It’s just as important to know the difference between kinds of brake fluids, which are known by different Department of Transportation (DOT) numbers.

The three main types of brake fluid include:

  • DOT3: This is one of the most common types of brake fluid. It has a glycol base and a lower boiling point. It also can absorb water from the air. Most vehicles can use DOT3 brake fluid.
  • DOT4: DOT4 braking fluid is similar to DOT3, but with a higher boiling point. This makes it a more efficient fluid. It’s also very common and can be used in a range of vehicles.
  • DOT5: When looking at DOT3 or DOT4 versus DOT5 brake fluid, the biggest difference is that DOT5 is a silicon-based fluid instead of glycol. It doesn’t absorb water like the others and has the highest boiling point. It’s not commonly used on road vehicles.

What Does Brake Fluid Look Like?

Regardless of its DOT number, brake fluid looks the same across the board. New brake fluid or fluid in good condition is clear and might have a yellow tint to it. It should remain relatively clear through routine checks over the years.

Brake fluid in need of replacement will get darker and darker. It generally will resemble motor oil – anything dark brown or black indicates that the fluid should be replaced.

Learn About Braking Systems at UTI

Changing your brake fluid is something that can be done at home, though it’s important to have some basic understanding of cars and to follow vehicle-specific instructions.

If you’re someone interested or passionate about the automotive field and are looking for a new career, then pursuing an education as an automotive technician could be the next best step to take.

In the Automotive Technology program at Universal Technical Institute (UTI), you’ll learn a range of skills that can help you in your day-to-day life and also your career.1 There’s an entire course on Vehicle Brake Systems that covers all things brake-related, including hydraulic systems and brake fluid.

You can learn more by requesting information online to get in touch with one of our Admissions Representatives, or by calling 1-800-834-7308.

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