What Is A Brake System Flush?

Many people assume when they have issues with their brakes it’s as simple as changing the pads and rotors. Do you know there is much more to maintaining your vehicle’s brakes? That’s right folks, your brakes consist of more than just brake pads, and one major component is the brake fluid. Brakes need fluid to function and that fluid needs to be changed once a year to keep your brake system operating correctly. A brake system flush will ensure that your vehicle’s braking system works at it’s peak level.

What is a brake system flush? This is a common question that gets asked by my customers when I tell them they need this service.

In this article I hope to answer some questions and show you why this service should not be ignored, here is what we will cover …..

Before we jump into what a brake system flush actually is, let’s take a second to learn a little about brake fluid itself and a little about some common brake issues.

Brake fluid is a glycol-ether based hydraulic fluid, there are mineral oil based fluids as well as silicone based (DOT 5)

However the fluid that is the most widely used is a DOT 4 or DOT 3 brake fluid.

There are a few things to know about brake fluid.

  • It is hydroscopic
  • It does not expand in high temperatures
  • It must have consistent viscosity at all temperatures
  • It must combat corrosion and protect rubber components in the brake system

Now I don’t want to get crazy into the chemistry of brake fluid in this article, however the examples above are very important to understand, they are a few of the main reasons brake fluid needs to be flushed.

Let’s take a look at how these affect the brake fluid in your vehicle.

Brake fluid is hydroscopic, this is the same as saying it absorbs water. Over time the moisture in the brake system builds up, the brake fluid retains this moisture naturally, hense (hydroscopic.)

I probably don’t need to tell you that moisture in your brake system will cause issues, over time the moisture starts to oxidize the fluid and turn it dark and nasty. On top of that if enough moisture builds up the fluid will lose it’s ability to not expand under heavy heat.

This can cause brake drag and overall loss of brake pedal “feel.” In essence, your braking system is less efficient and effective at this point.

As you can see we really put a lot on the shoulders of our brake fluid. The good news is quality brake fluid that is flushed every year will keep your brakes working properly.

Brake fluid works on the principal of hydraulics, in essence liquid does not compress. The brake fluid transfers the energy your foot applies to the brake pedal and transfers it to the brake calipers and rotors. This in turn converts the energy of your rolling vehicle to heat.

This is the simple short version but it does show that the real work is being done by the brake fluid.

So what is a brake flush? A brake system flush is the process of removing old brake fluid while adding new fluid behind it until the entire system has fresh fluid.

Each wheel has a bleeder screw that when opened lets the fluid flow out of the component, it can be the caliper or wheel cylinder.

Think of it as drilling a hole in the bottom of a bucket filled with water and adding fresh water in as the old runs out, the bucket always stays full so no air is introduced, however eventually the water in the bucket is all fresh.

This is the main goal when flushing a brake system.

There are three main ways to flush your brake system that I would like to run over real quick below.

#1 Pressure Flushing

Pressure flushing requires a tool that holds fresh brake fluid and air pressure on separate sides of a rubber diaphragm. Using a adapter that seals to the brake master cylinder the air pressure pushes the fresh fluid into the master cylinder as you open the bleeders at each wheel.

This is by far the fastest and most effective way to flush a brake system.

#2 Old School

Oh boy the old school way still works great, you need a friend in the driver’s seat. This simply is having a friend pump the brake pedal at least three times and them hold pressure on the pedal as you open the bleeder screws.

The name of the game here is keeping enough fresh fluid in the reservoir and making sure your buddy does not let the pedal up until you close the bleeder. It will take a few times at each wheel but the fluid will eventually flow clean.

#3 Vacuum Bleeder

Vacuum bleeding is the same principal except you are sucking the fluid out of each bleeder using a tool that is designed for the task.

Using a venturi effect there is a silicone line attached to the bleeder nipple that pulls the fluid out. Again you need to keep the master cylinder full enough so you do not suck air into the system.

I hope you have learned a little about what a brake system flush is in this short article. At the end of the day whether you take the project on yourself or pay a pro to get it done, you have made a good investment in your vehicle, and more important you and your families safety.

I recommend getting your brake fluid flushed every year with a good quality fluid that matches your vehicle’s specifications. You will enjoy a better stopping and driving experience.

Thanks for reading !