How To Rebuild a Master Cylinder on a Motorcycle or ATV

How To Rebuild a Master Cylinder on a Motorcycle or ATV

In this video we’ll demonstrate how to rebuild a motorcycle or ATV master cylinder. When your brakes fade or feel spongy, it’s usually a good sign your master cylinder needs a rebuild. The seals can wear out and cause air to enter the system, therefore drastically reducing your stopping power. Rocky Mountain ATV/MC carries all the parts and tools you need to get your breaks working at their full potential, including the OE parts for your machine. We’re only going to need a few standard tools to complete this job. It’s also a good idea to have your service manual handy. So we’ll start by removing the brake lever. This one has a mount on the bottom and it also threads into the master cylinder as well. As you pull it, watch for a spring and/or pushpin, as some levers will have them. That’s going to reveal the rubber boot. So to gain easier access to that, we’re going to loosen the master cylinder clamp bolts and slide it down the handlebar. For illustration purposes, we’ve also pulled our throttle tube and housing as well to better show the rebuild process. Now using a small screwdriver, go ahead and remove that rubber boot. Doing that is going to reveal a circlip. To remove that it’s easiest just to pull the master cylinder from the bars, and then use your circlip pliers to get down in there and pull it out. Notice we’ve got our finger on the piston to make it easier to remove. With the circlip out you can pull the piston assembly and spring from the master cylinder. We just zip-tied our master cylinder to the bars to keep it from leaking all over. So as you can see, the seal is obviously bad with a few small nicks in it. If you decided to go with an OEM rebuild kit, keep in mind each kit will vary with its included parts. They will usually always come with a piston, seals and spring. But you’ll just have to refer to your machine’s OEM diagram on our website for a specific list of parts. If you go with an aftermarket rebuild kit you’ll find they rarely include a piston, but they do come with the seals, spring and a few more parts to replace. You’d just simply remove your old seals from the piston and install these new ones included with the kit. We chose to install an OEM rebuild kit, which usually comes with everything. We just need to assemble it exactly like the one we pulled out. So we’ll put a little brake fluid on there to lube it up, and then slide that first seal down into place. Make certain the seal gets installed facing the right direction and into the right place on the piston. You may need to use a small screwdriver to help get it into position, being careful not to tear or damage either seal when installing them. Once you have the first one, move on to the other seal. Now we just have to install the spring and our piston is ready to be installed. We’re going to lube up both seals again before we slide on the washer and circlip, and then install the piston back into the cylinder. Make sure there’s smooth action before installing the circlip down into its groove. It’s always a good idea to use a small screwdriver to make sure it’s seated all the way. The next step is to re-install the rubber boot. Use a small screwdriver to seat that down into place. Now we can remount the master cylinder to the handlebars, and then reinstall our brake lever. Install that top pivot bolt and tighten it down. Then install the locknut on the bottom. It’s necessary to bleed the brakes after performing any kind of maintenance to the system. So first remove the reservoir cap and rubber gasket. And some reservoirs will have a little foam piece that sits on top of the fluid. Go ahead and pull that out and we’re first going to try back bleeding. We do this by spreading the break pads to try and push any air back up to the top of the reservoir. If this doesn’t work for you, you’ll need to bleed the system conventionally and you can refer to our other videos that outline each step to do that. It’s also a good idea to replace the fluid after you’ve done any work on the brakes. Old worn-out brake fluid can contribute to brake issues including overheating and fade. So we’re going to go ahead and change this fluid and finish bleeding these brakes. When you’re done your lever should tighten right up. Once you get to that point you’re done with the rebuild. And these steps would basically be the same if you’re rebuilding the rear master cylinder. So if you have any questions about your brakes feel free to give us a call at 1-800-336-5437 or visit us online Thanks for watching!

38 thoughts on “How To Rebuild a Master Cylinder on a Motorcycle or ATV”

  1. hi i have had my rmz450 (2007) for a few months now i do trail riding and last time i was riding coming up a big hill i went off to the side and hit a tree stump with my bars i wasnt going very fast and after that i had noticed my front breaks were completly squishy and no fluid was in the top fluid box. i couldnt see where the fluid came out but i tryed to refill and rebleed them when i got home there apeared to be no air in the line but the front break still remains squishy and doesnt work at all unless i slam them on quickly it will work for a second any idea? thanks

  2. can i ask you a motorcycle related question ? my bike would have pausing feeling when i apply the brake and when the bike only almost come to a stop.. i replace head bearing, wheel bearing looks fine, change rotors and pad,, still doing the same jerking thing .. what else i can do to fix that?  tire is balance and i bleed the brake als

  3. My 1981cb750c master cylinder cap is clear and can clearly see that it appears to be frozen because there is an angle to the fluid thats frozen inside. I should just buy

    and replace it or try to rebuild it?

  4. For those who don't have Cir-Clip Pliers. 

    When I was a kid (12 y/o) working on my 1965 Dream-Cycle, my dad didn't have Cir-Clip Pliers so I had to make something up. Scrounging in his tool boxes I came on this solution.
    * Take 2 long tempered finishing nails and grind the points flat.
    * Tape the heads together. Years later I found a rubber band works better.
    * Use a flat blade screwdriver to open the nails and insert into the Cir-Clip.
    * One hand hold the nails head, the other use (preferably) needle nose pliers to squeeze the nails together and remove/replace.
    . . . . . ENJOY!
    (IF this helped, I need help. I need surgery money to save my leg from DVT. I have no Insurance. PayPal fvm-usa(at)hotmail(dot)com GIFT .. .. small change helps)

  5. Awesome, my service manual was very vague and this showed me the correct order to reinstall the master cylinder kit. Thanks!

  6. what if the brake feels stiff? I can pull the brake and stopping power is good but just feels like stiff to pull lever

  7. I've got a 2005 yz250f. My front master cylinder is gone. Can I put on any old front master cylinder? Or does it matter

  8. I'd like to replace my Shimano Hydraulic Brake on my bicycle with chrome motorcycle brake levers/master cylinders. I am keeping the Shimano calipers and brake lines. Shimano uses mineral oil for fluid. Could you tell me if the seals on most motorcycles brake master cylinders are EPDM, Nitirle, or some other rubber compound? I know EPDM is not compatible with mineral oil.

  9. hi i have a honda 150 cc motorbike i have the same nissin master cylinder for front wheel. when i applied the break the cylinder will stuck inside never come back. please help me on this.

  10. Recently rebuilt my master cylinder and can't get any pressure to bleed brakes. The bore in the cylinder looked good without any damage when I did the rebuild. The only thing that I could see is if one of the seals rolled over while reinstalling the piston. If this was the cause should I replace the seals again?

  11. I'm wondering what would happen if I changed my ktm 300's master cylinder that uses a 10.5mm piston with a ktm 200's master cylinder that uses a 9.5mm piston? Would the clutch pull/feel be the same as it is on a ktm 200?

  12. 2003 Yamaha virago 250, been trying to bleed the front brakes for 45 minutes – gone through an entire small bottle of fluid and it's still not getting stiff. Is this likely a master cylinder issue?

  13. In an aftermarket kit, both cylinders are 14mm, dot 4 fluid got dirty black in just 15 days, properly bled it but again it went dirty black in just 1 day, what could be the reason ?

  14. I'm hoping this will work when I try to do this on my 2005 Ninja 636. The seal has to be bad as air gets in after each ride and I have to bleed it before the next ride everytime. I bought the All Balls one in your video which is just the rebuilt kit and joy the Piston. Hoping it all works well!

  15. I emptied my master cylinder to clean everything out as my bike hasn't been started in 4 years and may not have had any fluid changes since the factory(1994) removing the banjo bolt and covering that hole with my finger while pumping the lever does build up pressure but when reconnecting the line barely any fluid is coming out. Any advice?

  16. Down South squonks!

    Any tips on getting the piston pushed in so i can get the c-clip in? My 08' yz250 is so hard to get pushed in with washer and clip and get it set right! So annoying been trying for hours.

  17. Thanks guys, what a great video!
    I have one question though, what causes the small bubbles to form when pressing the lever? (at 4min27sec) My bike just started doing and Im not sure how to troubleshoot it… Thanks for your help!

  18. Where can I find a master cylinder for my front break? I’ve looked on Rocky Mountain and couldn’t find one. At least under my machine specific search for my dirtbike.

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