The internet is littered with video tutorials on how to bleed Shimano hydraulic mountain bike brakes. However, we wanted to share the real, professional way to properly bleed and flush a Shimano MTB brake that a highly experienced mechanic would perform. This method ensures that all of the bubbles are bled from the system, and also ensures that the dirty, contaminated mineral oil is flushed out and replaced.

In this video, Mike shares some projects around The Lost Co, chats with the shipping crew, and looks to see what bikes the mechanics are working on. Alex then shares how they perform a Shimano brake bleed and flush by doing a gravity bleed to flush out all of the bubbles and old, dirty fluid.

If you just want to learn how to bleed Shimano brakes, skip to 2:44

The first step is preparing the bike to perform the gravity bleed, which means getting the bike up in a stand with the front end elevated. We also use a securing arm to keep the bars from flopping around and keeps our lives a little easier when working on bikes all day. You’ll need to open up the top of the system at the lever and attach a bleed cup with brake fluid in there. Then attach a hose to the bleed port on the caliper connected to a bottle or bag or anything to catch the dirty fluid that will come out once we open the system.

The next step of preparing to perform a gravity bleed is actually performing a lever bleed.This is because there could be some dirty fluid at the lever that we want to catch before pushing it through the whole system. That also catches any air bubbles that have found their way into the lever body. Start with just a small amount of fluid in the cup while you’re performing the lever bleed so the little bit of dirty fluid that comes out doesn’t get a whole bunch of fluid dirty.

The last step of prep for the gravity bleed is pushing the pistons out a bit. This opens up the volume of space behind the pistons and allows for any trapped bubbles to free up. Opening up this space frees up the flow of the fluid to help coax the bubbles out of their hiding spaces. Now you’re ready to actually do the gravity bleed!

Fill up that bleed cup and remove your caliper from your frame to help the bubbles and dirty fluid negotiate their way out of there. Crack the bleed port open and you should see bleed port and bubbles start flowing out of the caliper. By starting with the bleed port at the lowest point in the system, the heavy fluid that’s contaminated with sediment will come out first, getting replaced with clean fluid at the top of the system. Air might be coming out right now, but our main goal right now is completing the flush of the system and fill it with that clean fluid. Start rotating the caliper until the dirtiest fluid is out, and as the fluid gets more clear and pink, you’ll be doing the flush and the bleed at the same time.

Give the lever some flicks to help nudge sediment and bubbles through the system, and make sure that the fluid in your master cylinder is not draining out completely! This would introduce air bubbles into the system and we would have to start over again with the lever bleed. Give the lever really slow pulses and you can watch the bubbles flow out. If you slowly release the lever as the bubbles are being pushed out, they won’t get retracted back into the system, helping you get them out for good. We also recommend tapping the caliper and lever with a soft tool to vibrate and agitate any bubbles to exit the system. This could be the rubber handle of a screwdriver or very soft taps from a rubber mallet.

Once there’s no contaminated fluid or bubbles coming out for about 30 seconds of flow, you can safely say that you’ve gotten all of the air out of the system. Go ahead and close the bleed port on the caliper and give everything a thorough wipe down before reinstalling your wheel, rotor, and pads.

Now we’re just going to perform a lever bleed to finish the process and ensure that the system is perfectly set up for your specific pads and rotor. Leave the bleed cup installed and give the lever a few flicks until no bubbles are coming out, and now you should be all done! You should actually follow this step every single time you change either rotors or pads to avoid creating a vacuum and cavitating your brake system.

Responsive brakes are absolutely the most confidence inspiring aspect of a dialed bike, and hopefully isn’t such a daunting task now. The steps are simple; gravity bleed from the top down, perform lever bleed before gravity bleed, slightly expose pistons before bleeding, remove caliper from frame to freely rotate it, keep bleed cup fluid topped off while fluids flows through system, install the rear wheel and brake pads before removing bleed cup from lever, and finally perform lever bleed again at the end.

Bleeding a brake is something every at home mechanic should have no issues with when you have the right tools, all of which we have here at thelostco.com!

Got questions? Feel free to shoot us an email or give us a call!

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