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Brake Bleed vs. Brake Flush: Which Is the Right Choice?

By Stephen Fogel, June 1, 2018

Your brakes are the most important safety feature on your car. It’s a hydraulic system that transmits the pressure of your foot on the brake pedal to the brake assemblies on each of the car’s wheels, forcing them to stop.

Brake fluid is what fills the lines that connect the pedal with the brake pads or shoes in your wheels. This fluid also lubricates the moving parts in the hydraulic system and protects against corrosion.

» JUMP AHEAD: Learn the differences between a brake bleed and flush, and find out which is right for you

In order for your brakes to work their best, it’s important to have the right level of brake fluid. You can find the fluid reservoir under the hood. Instructions for checking it and topping it up when necessary can be found in your owner’s manual. Use only the brake fluid type specified in the manual.

Does your brake fluid require any servicing?

Service of the brake system is part of factory-scheduled maintenance — check your owner’s manual to see what the manufacturer recommends. Most brake services are performed every 40,000 to 60,000 miles, or every two years, and the brake fluid typically is bled or flushed at this time.  

There are two primary reasons why brake fluid can go bad:

1. Moisture absorption

When is exposed to the air, it absorbs moisture. This is bad for your brakes in a couple ways:

While brake fluid has a boiling point of approximately 400 degrees Fahrenheit, any water in your fluid will boil at 212 degrees, creating gaseous bubbles that give your brake pedal a “mushy” feel and reduce your brakes’ effectiveness.

Moisture in the brake lines can cause corrosion in the metallic components of the system, which can result in damage and reduced braking ability.

2. Contamination

Brake fluid can absorb dirt from the atmosphere. It can also pick up metal and rubber particles from the wear of other braking system components. If you do a lot of hard stopping from high speeds, the heat produced can also degrade your brake fluid, breaking it down. This can darken its color, making it look burnt. 

Get it diagnosed by a professional
 

Bleeding your brakes vs. flushing your brakes

There are two types of brake fluid service procedures: bleeding and flushing. Many auto service shops, both dealers and independents, recommend a flush as the best way to service your brake fluid. Let’s take a look at both and see which makes more sense for you.

Bleeding your braking system

The bleeding process involves manually pumping enough new fluid through your brake lines to eliminate any air that may be in them. This can be done either by one person, using an external hand pump, or by two people, using the car’s brake pedal. The vehicle’s four brakes are bled individually, using a bleeder screw found on each caliper or wheel cylinder. People with good knowledge of hydraulic braking systems can learn how to bleed brakes themselves, or a mechanic can handle it instead.

Flushing your braking system

The brake flushing process goes a step beyond. Flushing replaces all of your old brake fluid with clean, new fluid. This procedure is often done with a powered flushing machine, which attaches to the brake fluid reservoir where the cap would normally screw on. New brake fluid is forced through the entire hydraulic system until the fluid that exits the system is clean. Flushing gives you all new brake fluid throughout your braking system.

» LEARN MORE: Get an estimate for your brake service

Which one should you choose?

Whether you bleed or flush your brakes, it’s crucial to never let air into the system or let the fluid level become completely drained. If you do the brake master cylinder will have to bled as well.

Here are a few guidelines on whether bleeding or flushing your brakes is the right way to go:

What does the manufacturer recommend? Check your owner’s manual or service booklet for the manufacturer’s suggestions on when and how to service your brakes. If there’s no recommendation for flushing your brakes, it’s usually not necessary, especially if you have followed the recommended service intervals and the fluid looks translucent or clear, not dark and murky.

Keep in mind that today’s sophisticated anti-lock braking (ABS) systems are designed to be totally sealed. The manufacturers are completely aware of the bad effects of moisture in their braking systems, and go to great lengths to keep it out. If you have checked and maintained your brake fluid level regularly, and had proper servicing done, you shouldn’t need to worry about flushing your braking system.

Are there signs of a braking problem? Have you noticed that your brake pedal feels squishy, and not firm? Does your vehicle require a longer distance to stop lately? Is your brake fluid dark, or does it have particles and debris floating in it?

If you notice any of these symptoms, get your car to your mechanic immediately. Have your braking problem diagnosed and repaired right away, before things get worse and you are totally unable to stop. If your fluid has deteriorated and needs replacing, then a flush is an appropriate step toward restoring the effectiveness of your brakes.

Bottom line: Don’t flush your brakes unless there’s a good reason. 

Many auto repair shops have come to regard an expensive brake flush as a profit center. They will suggest a brake flush to their customers as a part of every vehicle service. If your car’s manufacturer doesn’t require it, and you aren’t experiencing any braking problems, you can stay away from this largely unnecessary procedure.


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