A common Motorcycle maintenance task is to replace the hydraulic fluids in the brake and clutch systems. Hydraulic fluid will over time absorb water which causes the fluid to boil when the brakes are applied or the clutch is used, and thus reduce effectiveness of the system.
While you may consider this task to be complex, with a little knowledge and the right tools this maintenance item really isn’t that hard.
The primary tool you will want to invest into is a brake bleeding vacuum tool. This tool makes the job quick, clean, and easy. Along with this you will need a box end wrench that matches the size of the bleeding nipple on your motorcycle. For mine this was 10mm for the brakes and 8mm for the clutch. Of course you will need the appropriate brake fluid along with a container to hold the old fluid. Finally some rags and paper towels come in handy to catch any drips or dribbles.
Step 1: Refer to Your Service Manual
While the owner’s manual will often list most of the information you will need to do this job, there are a few things that will not be listed there and the service manual will contain the remaining needed details.
My owner’s manual included where the fluid reservoirs are located on my motorcycle and how to fill them to the correct levels. It also includes the grade of brake fluid to use, which is a very important detail. You may also find the service interval for fluid replacement which is usually ever two years.
For my motorcycle, the same grade (DOT 4) and type (brake fluid) is used in brakes and clutch systems. Make sure it’s a newly opened container of fluid. My motorcycle had one reservoir on the right handle bar for the front brakes. The rear brake reservoir was located under a body panel on the right side of the bike (many will have it on the left handle bar). The clutch reservoir was located under a body panel on the left side of the bike. I had to remove several body panels to get access to all the locations but the steps were all listed in the owner’s manual.
The service manual included how many bleeding nipples there are and where they are located. It also included the specific order I needed to connect to each one of them. My motorcycle had four nipples for brakes and one for the clutch. One was on the left front brake caliper, two on the right front brake caliper (one is linked to the rear brake), and one on the rear brake caliper. Further, it stated that the order should be front brake system, then the front for the rear brake system and finally the rear brake. Since there were two on the front system but it didn’t list the order, I searched online and found that the preference for the front is the left and then the right.
The amount of new brake fluid will depend on your motorcycle, for me since I was also doing my clutch; I picked up the larger quart container. You will also want to have a large container to put the old fluid into as the vacuum tool will get filled up several times during this process. Make sure you have plenty of rags/paper towels around also, while generally it’s not too messy, even a drop of brake fluid on a painted body part can cause damage, so laying down some protection before you do work will be well worth it.
Step 2: Bleed One System at a Time
The general concept is that you will be replacing all the fluid in the system by sucking new fluid through it. The new fluid will enter at the reservoir and the old fluid will be sucked out at the brake bleeding nipple. At no time do you want to get air into the system as this will require that you take extra steps to remove it. It is best to just avoid it in the first place.
Caution: From this point on, avoid activating the brakes when the fluid reservoir is open or low on fluid. When open and full it will cause fluid to squirt out of the reservoir. If the fluid is low enough in the reservoir when you release it will cause air to be sucked into the system. Simple avoid touching them and the rest of the task is pain free.
The first step is to remove the cover for the brake fluid reservoir and use the vacuum tool to suck out the old fluid in the reservoir. Just put the end of the hose in the reservoir and pump the tool. I put down some rags and paper towels around it just in case I would dribble a little fluid. If the reservoir has grit in it you will want to clean this out. Leaving a little fluid in the reservoir is ok; you will be refilling it with clean new fluid and sucking it through the lines several times so it will get removed.
Refill the reservoir with clean fluid from your new brake fluid container. Be prepared to keep it topped off as you do the next step so that the level never gets low enough to suck air into the system. Expect to refill each reservoir several times to make sure all the old fluid is removed from the system.
At the brake bleeding nipple, remove the rubber cover over the nipple, slip the box end wrench on, and push the vacuum hose onto the nipple. First pump the vacuum tool a few times to create a vacuum at the nipple (around 10 in Hg), and then turn the wrench to open the nipple. It doesn’t need to be turned far, ¼ of a turn is usually plenty. Remember the old saying “righty tighty lefty loosey”.
You will see the vacuum tool jar start to fill with fluid. This may happen slowly depending on vacuum amount and how far you have opened the nipple by turning the wrench. Keep the vacuum pressure near 10 in Hg. Take it slow until you get the hang of it. As it drains, make sure to keep the reservoir refilled. You can pause the process at anytime by turning the wrench and closing the nipple.
When the vacuum tool jar starts to get full, with the system still under vacuum, close the nipple by turning the wrench and the pull the hose off the nipple. This will suck the remaining fluid in the hose into the jar making it a little less messy when you remove the jar. Now remove the jar, empty it into your disposal container, replace the jar, and repeat the step to start bleeding more fluid through the system. Continue this until new clear fluid is flowing into the vacuum jar. It never hurts to pull more if you are unsure, better to be overly clean than leave some old fluid in the system.
Once new fluid is flowing; with the system still under vacuum close the nipple by turning the wrench and then pull the hose off the nipple. Then replace the rubber protector on the nipple and move on to other nipples on the same system.
Once you have bleed all the nipples on a system, refill the reservoir up to just below the top fill indicator with new fluid, replace its cover, and clean up any drips and you are done. Why not all the way to the top? If your system doesn’t leak, the fluid will slowly absorb moisture and expand, leaving a little room for this expansion is an easy way to spot that fluid should be changed again.
Once you have bled all the systems, it’s a good time to confirm all the nipples are properly tightened and all the reservoir lids are on tight. Finish up with a test by now activating the brakes and making sure they hold well. Also be cautious for the first test ride to make sure your brakes are working properly.
Step 3: Dispose All Fluid
That quart of new fluid was plenty for the three systems I had and I ran extra through to clear out the old. I was left with at least 8 oz that will never get used.
Remember to dispose all fluids properly. While any new fluid left over is ok for a bit, it should not be used after a few days from when it was opened as it will absorb moisture from the air. You should just dispose of the left over fluid with the old fluid.
Most automotive stores will accept the fluid. Search and you may find a disposal service that may take it also. Also check your community events for yearly collection services.
Now stand back for a second and enjoy your accomplishment, then quickly go get your helmet and gear and go for a ride!