How to Bleed Brake Fluid With a Pneumatic Vacuum Pump

Depending on the car part, air is crucial or extremely harmful. While an engine needs air to run properly, the reverse is true for a car’s brake system. To work effectively and efficiently, the brake system cannot have air in its modules and lines, otherwise the brake pedal will feel spongy or the brakes will not work at all. This is why you must bleed your brakes to remove air from the system each time the circuit is opened.

In the past, brake bleeding was a bit of a pain because it meant needing a second person to repetitively pump the brake system, but vacuum pumps eliminate the need for another body. Vacuum pumps are available with manual releases or with connectors designed to attach to an air compressor, making the job much easier. I recently bled my brakes with one of these air-powered vacuum pumps, and documented the process to show you how it’s done. Let’s go.

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Why you need to change brake fluid

Brake fluid is hygroscopic, which means it is attracted to water. Normally, a car’s hydraulic brake system is a closed system, but moisture and dirt inevitably enter the fluid. Water has a much lower boiling point than brake fluid, so under heavy braking water in the brake fluid can boil and significantly reduce braking power.

Separately, foreign contaminants in brake fluid can be hell for rubber seals. My old 2012 Sonic never had brake fluid until early 2020 at over 200,000 miles. The fluid was gnarly and had destroyed my Sonic’s master cylinder seals, so it was no longer needed. Instead of just needing a bottle or two of replacement fluid, I had to pay around $100 for a new master cylinder.

A vacuum pump eliminates many problems

I completely understand how boring it can be to use the two-pedal push-up method. I have horrible memories of being a 10-year-old sitting in the driver’s seat of a Ford Tempo or a Chevy Monte Carlo, while my dad or older brother yelled at me to hit the brakes on all my strength while my brother collected dirty liquid in a pot. My 10-year-old little leg strength wasn’t always enough to press the pedal down to the floor and hold it there.

Previously, bleeding the brakes was a two-person job, and it was a pain. Heck, that’s why I never did the brake fluid on my Sonic. But technology has come a long way, and we don’t need to enlist the help of prepubescent kids to change brake fluid. Recently I performed a quick brake fluid flush using a vacuum pump powered by an air compressor.

Brake Bleeding Basics

Estimated time needed: Less than an hour

Competence level: Beginner

vehicle system: Brakes

Safely bleeding brake fluid

Brake fluid is not good for skin or cars. If left on the paint, it can seriously damage the finish. Shop towels, a funnel, safety glasses and gloves are pretty smart ideas.

Everything you’ll need to flush brake fluid with a vacuum pump

As far as car maintenance goes, brake fluid flushes are pretty simple. You will need the following items.

Tool list

Product list

  • A few bottles of brake fluid, whatever your vehicle. It should be listed in the owner’s manual or on the brake fluid reservoir cap. My Fiat 500 Abarth uses the DOT 3 specification.
  • Brake parts cleaner

Here’s how to bleed the brakes with a pneumatic vacuum pump

Prepare your workspace, then follow these steps.

1. Raise vehicle, insert jack stands and remove wheel(s)

Place the vehicle on a flat surface, then use a jack to raise the car. You can lift one corner at a time, just the front or back, or all four corners.

2. Assemble the vacuum purge kit and find the purge ports

Attach the hose to the vacuum pump and the vacuum pump to the hose of the air compressor, then turn on the air compressor. Once that’s ready, locate the bleed port (it should be at the back of the caliper) and remove the dust cap/sleeve.

2. Connect the suction hose to the purge port

Start with the wheel farthest from the master cylinder. In my case, the master cylinder is on the front driver’s side of the car, which means the passenger side rear wheel needs to be bled first.

Connect the air hose to the port. Make sure the capture cartridge is screwed on tightly to ensure a good vacuum seal.

3. Drain and replace fluid from main brake fluid reservoir

Locate your main brake fluid reservoir in the engine compartment. The vacuum can be used here, but some prefer to use other tools, such as a hand-held liquid extractor or a turkey baster. Either way, open it up and get all that dirty, yucky fluid out of the reservoir and replace it with fresh fluid. Keep the cap loose to allow airflow, but keep it above the reservoir to prevent contamination.

As you remove fluid from your brake lines, keep an eye on the reservoir and add fluid as it goes down. You don’t want to let the main brake reservoir dry out, as that allows fresh air to enter the system, which defeats the purpose of this process.

4. Flush the brakes

Using your wrench or socket, loosen the brake caliper bleed screw about a quarter turn. With the vacuum attached to the purge valve, turn on the vacuum and draw out the liquid.

Again, be sure to check the brake fluid reservoir. It will decrease as new fluid is drawn in and passes through the system. Top up brake fluid as needed and do not let the fluid level drop below the minimum.

It’s a little hard to judge when a wheel cylinder is done using this method, but you’ll want to drain (and replenish) until the sucked fluid changes from yucky and dark to light yellow or clear OEM.

5. Close the bleed valves when each wheel is finished

When the fluid looks good, remove the hose, use your wrench to tighten and close the bleeder valve, replace the cap and move on to the next wheel cylinder. It’s not a bad idea to spray some brake cleaner on the valves as well.

6. Check all fluid levels and test the brake

After bleeding each wheel cylinder, check the brake fluid reservoir again and make sure everything is at the correct level. If all is well, get in the car and hit the brakes. The pedal should feel firm, with no sagging or weird movement.

If you did everything right, the brake pedal feel should be the same as before (maybe a little better), and now you can sleep soundly knowing your brake fluid isn’t black.

Video

For those who can’t or don’t want to read, we’ve selected a video that demonstrates the process we discuss above. Check it out.

FAQs

We want to try to answer all your questions before starting work. We’ve selected common points of confusion from our experience, as well as frequently asked questions in popular search results. We’ve answered these questions below.

Q: How often should I replace my brake fluid?

A: Each car and manufacturer may have slightly different lead times, so check the recommendations in your owner’s manual or online. In general, a good rule of thumb is every two to three years.

Q: Should I use a vacuum pump?

A: No, you haven’t, but this vacuum pump certainly makes a quick job of a tedious job. I was able to flush my brake system in about 35 minutes, probably a third of the time if I had used the traditional two-man pump and dump method.

Q: Do I need an air compressor to use this tool?

A: Yes, to some extent. You will need something that can create a consistently strong vacuum. In my case, I used an air compressor which is also suitable for pneumatic tools. Others have used AC exhaust compressors or even an electric bicycle pump.

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About Marion Alexander

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