How to Change Your Motorcycle Brake Fluid (and Bleeding the Brake Lines)

brake fluid
Keeping your motorcycle brakes healthy is critical to your survival.  No joke.  So, it is important that when your brakes are starting to feel squishy (a sign you have air in the lines) or your brake fluid hasn’t been changed in a while, to do a little preventative maintenance.  Good rule of thumb is to bleed your brakes once a year.

Also, if you are leaking brake fluid anywhere (…..and I mean anywhere), it is important to address the braking system as a whole.  Leaking fluid means not only that you are losing fluid (duh!), but that air is probably getting into the system.  This is bad for overall stopping performance.

Today, we will go over the basic fluid change assuming the braking system is generally healthy.  However, I am currently in the process of completely rebuilding my Shovelhead’s rear master cylinder and rear brake drum.  We will go over these projects and others necessary to overhaul brakes in separate posts.

Steps to Change your Motorcycle Brake Fluid (and Bleeding the Brake Lines):

1) Determine the brake fluid you need (DOT3, DOT5, etc).  This is sometimes stamped into the master cylinder reservoir cover or plug (that’s the little box on the handlebars by your right hand for your front brake and the little box down by your right foot for the rear brake – locations can vary slightly).  Your shop manual or the internet is also a good way to determine the right fluid to use.  It is very important not to mix brake fluids.  A few of the grades can be mixed, but it is better to be safe than sorry.  If you were using DOT3, continue using DOT3.  If you were using DOT5, you get the point.

2) Prepare the bike and yourself.  Brake fluid will take paint right off a tank or fender and can be quite irritating if you get it on your skin, so I suggest getting gloves and covering sensitive areas of the bike with towels and/or plastic.  SERIOUSLY, nothing would be worse than having to repaint a front fender because you didn’t take the necessary precautions.

3) Fill the reservoir with fluid.  Remove the cap from the top of your master cylinder and make sure to keep the reservoir cap and rubber diaphragm or washer clean and in a clean spot.  Only use a new bottle of brake fluid (brake fluid that has been sitting reacts with the air and shouldn’t be used).  Brake fluid can be obtained at your local auto parts store.  I recently picked up a bottle of DOT 3 at my local Home Depot.

4) Setup: Find the nipple connector on your caliper that isn’t connected to anything.  It should stand out because you will be thinking, “it looks like a hose should connect there.”  Well, a hose does connect there for this very purpose.  Put one end of a clear plastic tube over the nipple and run the other end down into a clear jar with some brake fluid poured into the bottom.  The lower end of the tube should be below the level of the brake fluid (so as not to suck air back into the system).

5) Bleed the Brakes: Pump the brake handle a few times.  Loosen the nipple approximately one turn and gently pump the brake lever.  This will cause fluid to flow through the tube and down into the jar.  Fluid may need to be topped off during this process.  At first you will probably see old fluid and air, but eventually there will be no more air bubbles.  Tighten the nipple, squeeze and hold the brake lever, and open the nipple again.  If no air bubbles or fluid comes out, you are all done.

6) Finish: Once you can complete Step 5 with no bubbles it is time to start cleaning up.  Refill the reservoir and replace the reservoir cap or plug with its diaphragm or washer. Make sure the master cylinder is filled at all times or you will simply be sucking air back into the system.

As always, if you have any questions, please feel free to reach out.  Also, please share on social media.  Thanks and safe riding people!

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