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Your car uses a hydraulic braking system to slow and stop the vehicle, but what happens from the time your foot presses the brake pedal to the time the car stops? Keep reading to learn about the brake system on your vehicle, how it does what it does, the importance of brake fluid in that process, and the cost of replacing brake fluid in a car. 

The Cost to Change Brake Fluid

The average car will use about a quart of brake fluid to flush the system, so the cost will be between $10 and $20 for the brake fluid. If you decide to take your car to the mechanic instead, the labor can range from about $50 to $100 in addition to the fluid. Generally, a brake fluid flush is around $100 when you have a shop do it for you. 

When it’s time to do your brake flush, get all your brake fluid at AutoZone, as well as tools and any other parts that you need to keep your car on the road. 

What Does Brake Fluid Do? 

The term hydraulic comes from the word hydro, which means water in Greek, and in modern usage, it pertains to anything using a fluid to do work. The hydraulic brake system on your vehicle uses brake fluid to compress brake pads against rotors at the wheels, slowing and stopping the car. The fluid is pressurized in the master cylinder of the vehicle when you step on the brake and sent to the calipers at each wheel through a system of pipes and hoses. 

For almost 100 years, brake systems in cars have relied on the pressure from the driver’s foot to actuate the master cylinder, but in recent years brake by wire technology has been developed, and now more vehicles are seeing a change to electronically actuated master cylinders. 

What are the Different Types of Brake Fluid? 

There are four different types of brake fluid available, and they all use the prefix DOT, standing for Department of Transportation, in their naming conventions. This is because the DOT maintains standards for their quality and safety through regulation of specifications. 

  • DOT 3 brake fluid is a glycol-based fluid that has a dry boiling point of 401 degrees F and a wet boiling point of 284 degrees F. We’ll explain why that matters in the next paragraph. 
  • DOT 4 brake fluid is also glycol-based, with a dry boiling point of 446 degrees F and a wet boiling point of 311 degrees F. 
  • DOT 5.1 brake fluid is glycol-based, with a dry boiling point of 500 degrees F and a wet boiling point of 365 degrees F. 
  • DOT 5 brake fluid is silicone-based, so it is incompatible with any of the other types of brake fluid! It has the same boiling points as DOT 5.1 brake fluid. You cannot use DOT 5 fluid in a car that calls for any other type. 

Why do Brake Fluid Boiling Points Matter? 

The dry boiling points are measured with fluid that has not been exposed to the atmosphere and has not absorbed any moisture. The wet boiling points are measured using a fluid that has been contaminated with 3.7% water. 

All the glycol-based brake fluid types can absorb water, when you open the brake fluid filler cap, through rubber hoses, or worn seals. Heavy braking can cause your brake rotors, pads, and calipers to heat up, even to the point of boiling the moisture in the brake fluid. When the moisture in the brake fluid boils and turns into a gas it can reduce the ability of this system to pressurize the brakes and can lead to brake fade. 

For this reason, it’s the wet boiling points of the fluids that matter, because they represent the real-world temperatures at which the fluids can still be effective. 

Which Type of Brake Fluid Should I Use? 

Always consult the owner’s manual for your vehicle to determine the correct fluids for use in your brake system. It may even indicate on the top of the brake fluid filler cap as to which fluid you need to use for your particular vehicle. Most vehicles will use either DOT 3 or DOT 4 fluid. 

How Often Should I Change the Brake Fluid in My Car? 

A brake fluid change is part of the normal maintenance schedule of every vehicle because as moisture continues to enter the fluid it becomes less effective, and it can eventually wear out. For most passenger cars, a brake fluid change interval of every two years works very well. If you take your car to the track or live in a mountainous region where the brakes take a lot of punishment, you may consider changing the brake fluid once a year or more. 

When it’s time to do your brake flush, get all your brake fluid at AutoZone, as well as tools and any other parts that you need to keep your car on the road. 

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