How to Change Motorcycle Brake Fluid

How to Change Motorcycle Brake Fluid

Recently, the National Highway Traffic Safety Administration has reported that they are investigating brake failures on Harleys from the years 2008-2011.  While they have yet to conclude what the exact causes are for the 43 reported cases, the NHTSA has noted that it is possible that the failure was due to the riders not changing the brake fluid every two years, which is what is recommended by Harley.

Now be honest.  Do you change your brake fluid every two years?  Have you ever changed your brake fluid?  If you do, you’re on top of things.  If not, you’re probably among good portion of the riders out there.  For some reason, changing brake fluid is one of those overlooked maintenance tasks on motorcycles.  It’s one of those, “if it’s not broke, why fix it” sort of things.

So why should you change your motorcycle’s brake fluid every two years?

In short, the answer is because brake fluid degrades over time and can be rendered ineffective.  Almost all brake fluid used in motorcycle brake systems is Glycol based and is hygroscopic.  That means that the brake fluid will absorb moisture when it is exposed to it, even if it’s through the air.  And even though your brake system is a “sealed system,” moisture can make its way through seals and hoses over time.

As the brake fluid absorbs more and more moisture, its boiling point is lowered and it becomes less effective as it warms.  At this point, the stopping power can be greatly diminished and leave you grabbing a squishy lever when you need to stop.  That’s not a good feeling.

Fortunately, changing the brake fluid on most motorcycles is a fairly easy process and can be done with a minimal amount of tools and wrenching skills.

Brake Bleeder

Tools/Equipment Needed

What makes this DIY friendly task is the fact that you don’t need any fancy tools or equipment to change the brake fluid in your motorcycle (though, those specialized tools do exist).  To start, you will need your handy owner’s manual, a Phillip’s screwdriver, a box wrench, a clear piece of hose that will fit over the bleeder bolt (about a foot or two of hose should be sufficient), a spill-proof container (a glass jar with a hole in the lid works well), shop rags and new, unopened brake fluid.  A vacuum bleeder can be used to speed up the bleeding process.

Step One

Use a shop rag to clean around master cylinder to help prevent any debris from entering the brake system.  Next, use another clean rag or towel to cover any bodywork and finished parts on your motorcycle that are near the master cylinder.  Brake fluid is highly corrosive and can damage the finish of your motorcycle in a hurry.

Step Two

Use the screwdriver to remove the master cylinder reservoir cap.  Then carefully remove the diaphragm and diaphragm backing plate.  Place these parts on a clean rag and out of the way.

Step Three

Remove the rubber cap from the bleeder bolt located on the brake caliper.  Then slip the closed end of the wrench around the bolt.  With the wrench in place, attach the piece of hose to the bleeder bolt and route it into your draining container.

Step Four

Pressurize the brake system by pumping brake lever a few times.  Then with the brake lever pulled in, crack the bleeder bold just loose enough to allow pressurized fluid to come out until the lever comes back to just before touching the handlebar.  Tighten the bleeder bolt and release the lever.  Fill the reservoir back to the full line with fresh unopened brake fluid.  Re-pressurize the system by pumping the brake lever until it is stiff again.  Repeat the bleeding and filling process until the fluid runs clear and with no air bubbles present in the fluid.

Step Five

Top off the brake fluid so that it is at the full line in the reservoir and reinstall the diaphragm backing plate, diaphragm and reservoir cap.  Wipe down the master cylinder and around the bleeder valve to ensure no fluid is left on your motorcycle.


Use the recommended brake fluid for your motorcycle.  Each type has a different boiling point range and is only appropriate for certain applications.  Most motorcycles use either DOT 4 or DOT 5.1 brake fluid (DOT 5 is silicone based and should not be used unless it is specified in the owner’s manual).  Most automobiles use DOT 3 fluid, but its lower boiling point is not suitable for motorcycle applications.

While bleeding the system, be sure to not drain the master cylinder completely.  Doing so will allow air bubbles to enter the system.

In brake systems with linked front and rear brakes or in systems with multiple calipers, start with the caliper that is farthest away from the master cylinder.  If you are not sure, refer to your owner’s manual.

Use fresh unopened brake fluid.  Even opened fluid that is stored with a cap on will absorb moisture and degrade over time.

Where to Discard Used Brake Fluid

Brake fluid is highly corrosive and flammable and should be discarded with care.  Most waste collectors allow you to mix the brake fluid in with used motor oil and they can be recycled together.  So most places that accept used oil should also accept used brake fluid.  Some auto parts stores may also accept used brake fluid to be recycled.


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