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Thread: How-to Bleed your Hydraulic Clutch

  1. #1
    Site Founder crashtd's Avatar
    Join Date
    Jun 2008

    How-to Bleed your Hydraulic Clutch

    Hands up who has had or is having hydraulic clutch or rear brake problems.

    OK hands down, I think that is all of you, so here goes a step by step guide to cure your woes
    The problems on the clutch are caused by vertical layout and the small displacement of fluid by the master cylinder. On the rear brake the volume displaced is smaller still.

    It is virtually impossible to properly bleed a motorcycle clutch or front brake using pump the lever and crack the banjo method. Vacuum systems are a much more capable method, but their cost outweighs the advantages for part time mechanics.

    Here we have a method on a budget simply using a plastic medical syringe, of from 10 to 75 ml, you can use reverse fluid injection to effectively bleed any motorcycle brake or clutch in very little time.

    Ensure your reservoir is clean and free from contaminates (pumping dirt into your lines is not good). Extract all the fluid out of the reservoir and clean. Take your clean syringe and fill it with new brake fluid. Attach it with a clear vinyl tube to the bleeder at the caliper or clutch slave. Open the bleeder and inject the fluid while watching the level in the reservoir. Stop when full. Close the bleeder. Suck out the reservoir and repeat as needed. Job done, how easy was that .

    One last thing about bleeding clutches. There is not actually a bleeder on the slave cylinder itself. It is part of the banjo bolt. it is possible to bleed and still have a pocket of air within the slave cylinder. It is however easy to remove it.

    After bleeding as above and filling the reservoir, remove the three screws securing the slave cylinder. Remove the cylinder and hold it in its normal attitude then tip it slightly to the right (as if you were leaning the bike to the right). Allow the internal spring to slowly push the piston out 5 or 6 millimeters and push it back in forcefully. Be careful not to spill any fluid on your paintwork. Repeat this several times. Reinstall the cylinder you may want to reverse inject just for good measure. (do not overfill your reservoir, when hot it expands and can cause a slipping clutch)


    Article kindly used with permission from KZmille (Author)

  2. #2
    Site Founder crashtd's Avatar
    Join Date
    Jun 2008
    From our own OldTLSDoug:

    I just finished the kzmille method and it is absolutely spot on. I am truly impressed, here is my story.

    I bought a syringe for $0.89, I had a quart of brake fluid. I bought the new seal locally, for $22.37. I read this entire post and the bulletin kzmille posted and spend some time trying to find some "silicone o-ring grease" Finally got it at Loews for $2.99 or so.

    Moment of truth, I sucked the reservoir dry with the syringe, then sucked the slave and the line down via the bleeder. I popped off the slave cylinder and saw the muck and goo. I lubed up the new seal, filled the slave with brake fluid, inserted the piston and pushed it until the thing was in far enough to raise the level in the reservoir. Then I pressure filled it from the bleeder bolt for about 3 cycles. Then I pulled the slave off and pumped it hard 5 times, then bolted it back, pressure bled it 3 or 4 times more, then pulled it off and did 5-7 more compressions. Then I bolted it back on, filled the reservoir to the middle. I fired up the bike, and the clutch felt way too light to be working, so I gingerly put it in gear and WOW! It works perfectly. I took a short spin and I would say the lever effort is 20% less and it is much smoother. So, my hat is off to kzmille. I made the tool for the rear brake shown in the service bulletin today, and tomorrow I plan to bleed it out. Much easier than even using the Mity-Vac. Thanks for the simple method for a simple old guy.

    Here are a couple of pictures, click the picture for a big 'un

    dirty slave cylinder. It was perfectly smooth and not marked at all after I cleaned it.

    Here is the piston, note the black crap, it was easily wiped off, but it was the residue from the seal breaking down and cleaned up nicely.

    The end of the piston where the clutch pushrod goes.

    Finally, the spacer and the clutch pushrod.


  3. #3
    Baby Twin
    Join Date
    Jul 2014
    Colorado Front Range

    help with clutch bleeding.....

    OK, so what am I doing wrong?? I'm trying the "injection" method and, after opening the bleeder, the fluid will STILL not inject into the master cylinder. Now I can't even bleed it in the "normal" fashion. Too much air in the system. HELP!!

    Quote Originally Posted by crashtd View Post
    From our own OldTLSDoug:


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