How to Change Brake Fluid (Complete guide)

The average car owner doesn't seem to know enough about brake fluids. Most drivers and car owners don’t even know how to check the fluid, neither do they recognize when it’s time to change or replace the brake fluid. Little has been said about the risk such ignorance poses to all road users. At every point in time, the brake fluid - and, by extension, the whole braking system - must work optimally at high pressures and temperatures.

There are elements (e.g., high-stress and high-friction) present to make sure this doesn’t happen but can make sure they don’t have the final word. You can do this primarily by routinely checking and maintaining it and replacing it as the case may be. This article provides a thorough inside scoop of brake fluid and how to change it.

What is brake fluid?

brake fluid change

Brake fluid is what a vehicle uses to translate pedal force into pressure to aid the brake's overall force. Summarily, when your foot presses down on the brake pedal, the fluid transfers the force generated as pressure to the front and rear brake (especially the front as it bears the brunt of the braking task), which then brings the vehicle to a stop. It’s a type of hydraulic fluid found only in hydraulic brake applications in cars. For it to work well, it has to remain liquid throughout the process.

To find out everything about brake fluids including types of brake fluid, the best brake fluid, and the most common questions about brake fluids, read this article.

How does it work?

Foremost, every wheel in any vehicle has its own assigned brake. For your vehicle to come to a halt without hassle or incidents, all four of them must work in seamless unison. As has already been mentioned in this article, the front brakes perform a more important function than the rear ones, and accordingly, brake discs go to the former, while the less efficient brake drums go to the rea.

As soon as you apply your foot to the brake pedal, a piston in the master cylinder experiences a depression. The brake fluid then pushes the depressed piston out of the master cylinder and onto the brake. It’s the brakes that go on to stop the car. Two crucial points should be noted at this juncture, and they are:

  1. It’s not every braking system that needs fluid, the electromagnetic braking system, for example. Brake fluid is peculiar to the hydraulic braking system and every car that uses them.
  2. This hydraulic braking system is useless without fluid. If there is no fluid, then there will be no pressure. And without pressure, your vehicles can’t stop.

Choosing the appropriate brake fluid

Brake fluid change

When it comes to brake fluid change, choosing the ideal fluid remains vital. This fluid has its variations too. Each one is markedly different from the other. The suitability of fluid with the vehicle’s braking system is important when carrying out a replacement. Manufacturers design every car in such a way that it can only work with a particular fluid type. Avoid mixing and matching in any form.

Types of brake fluid

There are four main types of brake fluid and they are DOT 3, 4, 5, and 5.1.While 3, 4, and 5.1 are glycol-based, 5 is silicone-based. The primary difference is that while 5 doesn't absorb moisture, 3 and 4, and 5.1 do, which means that they are hygroscopic.

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Characteristics of a good brake fluid

Brake fluids must have certain characteristics and meet industry standards if the braking system must work properly. In order to make the right pick to change brake fluid, take note of the following attributes:

High boiling point

In the process of working to bring a vehicle to a stop, the brake fluid often experiences an incredibly high level of temperature. Especially so in the wheel cylinders of both the brake drums and brake discs calipers.

For the liquid to avoid vaporization within the lines, it must have a high boiling. Vaporization is a problem that fluid is supposed to remain so for the braking system to function properly as vapor is not compressible.

However, Vapor is readily compressible, which is a problem because it goes against the hydraulic transfer of braking force, which causes the brakes to fail.  Brake fluid has to stay fluid at all temperatures, however high.

Low hygroscopic

As initially stated, there are broadly two types of fluids: glycol-based and silicone-based. While the former absorbs moisture from the atmosphere, the latter doesn’t. Most of the brake fluids in use today are glycol-based, which means that they are hygroscopic, though to different degrees. They begin absorption the moment they are exposed to air or placed in the hydraulic brake system. A good fluid will only absorb small amounts of moisture over a long period.


Brake fluid shouldn’t be to the metals used inside surrounding components like calipers, wheel cylinders, and master cylinders. A good fluid is designed to protect against any corrosion form even as moisture enters and aggregates in the system. Additives (a substance that is made to inhibit corrosion) can be added to the fluid’s base to help achieve this.


Good brake fluid should be able to stay fluid. When push comes to shove, it should exhibit a shallow compressibility level, bothering on the insignificant. This is irrespective of temperature. The fluid's ability to maintain low compressibility is crucial to the consistency in the brake pedal feel.

High viscosity

brake fluid change

Viscosity refers to the thickness of the fluid, which directly impacts its resistance to flow. Good brake fluid must retain a constant viscosity when it’s subjected to a wide range of temperatures. This is critical for the proper operating of the hydraulic brake system operation.

Brake fluid contamination

Brake fluid, in many ways, is like any other fluid in your vehicles. And like them, it should be replaced. Typically, it’s subjected to contamination of various kinds, including the deterioration of hoses and lines. Contamination can also result from increased temperature generated during braking fries the caliper and wheel cylinder's oil. All of these lead to a rather poor braking system. Contamination can also result from moisture and air.


In the hydraulic braking system, air contamination can come about in several ways. First of all, it results from poor bleeding of the fluid, which leaves contaminated air in the system. It’s considered by technicians to be the primary cause. Another way is for air to sneak in via worn-out seals and components.


The hygroscopic glycol-based fluid absorbs moisture before and during operation. This is a result of the design and not a bug. The molecules of the moisture will otherwise cause rot to other internal components in the braking system. Over time, when the fluid absorbs moisture, it begins to experience reduced performance. This is the more reason why fluid should be routinely changed.

How to change brake fluid

When it comes down to it, your vehicle's brake fluid will need to be changed irrespective of whether the contamination results from air, moisture, temperature, or any other extraneous material.

Get the right replacement brake fluid

Different vehicle houses varying braking system. For instance, heavy-duty vehicles like SUVs and trucks typically require a strong braking system. The main reason for this is so that they can withstand very high temperatures. Light-duty vehicles, on the other hand, may only require a fairly moderate braking system. Accordingly, varying braking systems are suitable for different fluid types. Whenever in doubt, consult your owner's manual.

Prep your vehicle

Once you have acquired the suitable fluid, the next step will be to get your vehicle ready for the fluid change. First, lift the vehicle off the ground with the aid of a jack stand and hydraulic floor jack. Your jack stand must be correctly situated at the safe lifting points underneath your vehicle.

While your vehicle is suspended, carefully remove your tires and put them aside. It’s essential to note where every tire was taken from to be duly returned during assembling. Otherwise, it will mess with your vehicle’s alignment.

Bleed the brake lines

There is a bleeder valve on each of the four brakes (it looks like a miniature plug). Open each of them using a wrench or a vice grip. As soon as they open, attach your bleed kit to the mouth of the valve and commence bleeding the brake fluid. It should be noted that the bleeding is to follow a specific other. Start with the one farthest from the vehicle’s master cylinder.

Continue bleeding in descending order of proximity to the master cylinder until all old fluid bleeds out. After every complete bleeding, fill in the replacement fluid until it reaches the fill line. Replace the reservoir cap immediately you finish to prevent air contamination.

Pump the brake pedal

When you complete replacing the fluid, pump the brake pedal to enable the master cylinder to work the new fluid around your whole braking system. Pumping the brake pedal between ten to fifteen times should do.

Test your work

The next and final step should be driving the vehicle. If it’s working perfectly, then you have done a good job. If not, you’ve done something wrong, in which case you may need to redo it or take it to an expert mechanic.

How often should brake fluid be changed?

It goes without saying, brake fluids should be checked as frequently as other fluids in your engine are checked. Most vehicle manufacturers and industry experts agree that fluids, especially glycol-based ones, changed every one to two years. Sometimes, your brake starts to malfunction before the suggested one to two years. There are ways to confirm if the fluid is faulty or not, and they are listed as follows.

Moisture content

When the fluid's moisture content is confirmed to be more than 3.5 %, the fluid should be replaced. The new fluid used should always have been stored in a sealed container to avoid moisture intrusion.

The copper test

When fluid is contaminated with moisture, the first metal that it corrodes is copper. So, once the copper ion gets to 200ppp, know that it’s time to change it.


By just checking the fluid reservoir, you can tell if the fluid level is enough or low. If it’s low, it could result from fluid leaks, which could cause the vehicle to lose hydraulic pressure and eventually braking capacity.

Dirty fluid

Color may also be a great indicator of when fluids should be changed. The dirty fluid typically means it’s time for a suitable replacement. The range of colors for dirty fluid is from dark brown to black.

Cost of brake fluid change

It generally cost to change the fluid in your vehicle roughly the same for all brand or model of cars. The cost is quite affordable as it tends to fall between $80 and $120. The bulk of the cost is paid for the craft. You can, however, save on that if you have the technical know-how.

Key Takeaway

When it comes to deciding which brake fluid to purchase, it’s good sense to stick with the type that’s already in your system or listed in the vehicle’s manual. Also, keep in mind that even though the fluid may meet the DOT specifications, it, more importantly, has to be compatible. Lastly, mixing is not by any means recommended. If you lack the necessary technical know-how to change the fluid, employ the help of professionals.

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