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  • Front Master Cylinder Rebuild Woes

    All,

    My front brake lever was binding and sticking whenever I was braking, so I figured I needed to install a new master cylinder rebuild kit. However, after install, I get no pressure at the lever whatsoever. I have been trying to bleed the system, but seem to get a lot of air... but I am not sure if that is just because of a poor connection between the nipple and the bleeding hose, or if there is a leak somewhere. In any event, not sure why installing a rebuild kit would suddenly cause a leak lower down in the system.

    I actually have replaced the rebuild kit twice... I ordered a rebuild kit, but before it arrived I found one that I had ordered a year or so ago and forgot about. So I installed that one, no pressure at brake lever, figured maybe something was wrong with the rebuild kit, so took it out and installed the second with same result. I have examined the brake lines to see if there is any indication of a leak, but I don't see anything, and, again, didn't really pull any of the brake lines. When I originally installed the rebuild kit, I dismounted the master cylinder from the handlebar, but didn't disconnect it at the banjo... left it connected so I wouldn't have to worry about possible leaks... I thought.

    So, to sum up, here are what I think are key details:
    • I drained the system enough to remove fluid from the master cylinder, but didn't totally drain the system.
    • I removed master cylinder from handlebars, but left connected at the banjo.
    • Removed old piston and seals, replaced with rebuild kit. Spring, seals, piston and boot. Remounted on handlebar.
    • Bled brakes using vacuum pump. Got a lot of air, and then solid fluid, but fizzy air... seemed to be air leaking in between nipple and vacuum hose? or sign of leak somewhere?
    • Disassembled again, this time removing at banjo on handlebar.
    • Installed new rebuild kit.
    • Remounted, torqued banjo to spec, bled brakes, same result.
    Any thoughts on possible solutions would be greatly appreciated. Thanks in advance!

    RTT

  • #2
    They can be a real bitch to bleed. Take your tee fitting loose tap on it and the lines. Letting it sit overnight may help too. It took me flushing nearly a whole bottle through to get mine bled after I did the rebuild kit and now the brakes are so smooth and zero hangups. You'll get it, just will seriously try your patience!
    2000 Roadstar 1600 - BAK, Pumpless, Curt's manifold, Mikuni HSR42 Freedom Combat Pipes Jumbo Strong bags, PPG 'HellFire' Paint.

    Comment


    • #3
      Try bleeding it at the splitter. That is a common spot for a trapped air bubble.

      Comment


      • RTT
        RTT commented
        Editing a comment
        Thanks! I've been tapping at at the splitter to see if I can force air bubbles out... didn't know you could bleed it there, will take a look.

      • davej
        davej commented
        Editing a comment
        yep just crack it open while you are pulling the lever. Make sure the fender is covered REAL GOOD so no brake fluid gets on it and destroys the paint. If any gets on it rinse it off immediately.

    • #4
      Using a powered vacuum bleeder is the best. Not a mighty vac... But one that hooks to an air Compressor. I use this and Prestone DOT 4 synthetic fluid with great results. My latest Road Star had a shitty front brake.. Felt crunchy... Had wrong fluid in it. Bled the system filled MC with brake cleaner and sucked it through the lines on both sides... Did this twice. Let it sit for 30 min opened up. Filled with fresh Prestone DOT 4 synthetic ran 2 MC worth of the fresh fluid through and perfect brakes. Also took the lever apart and cleaned and greased.

      Using a powered bleeder made doing brakes on My Road Stars over the years MUCH easier than with a mighty vac or other manual way. I do like speedy bleeders also...seem to seal better than factory bleeders.
      LET'S RIDE

      Comment


      • RTT
        RTT commented
        Editing a comment
        Power bleeder? I'll have to check that out, getting tired of hand pumping the mighty vac. Now if I can only get the damn hose to stay on the nipple. Thanks!

    • #5
      When you say no pressure whatsoever, do you mean all the way to the handlebar/front wheel still turning or some braking with a mushy brake lever?

      If you have a leak somewhere along the lines I think you would see it if you were pumping from above rather than Using a vacuum...but it would have to be a massive leak to result in no pressure in the brake lever.

      I agree with the others that this is a hard system to bleed. The t and the banjo at the master cylinder Are both places where I think I have had air hang up because bleeding both of those places made it better but I was improving on bad pressure not no pressure.

      With the lever binding and sticking maybe it has something to do with the piston (bent or scored?) causing the new seals not to seal. Just a thought but I don’t know how the piston could get damaged.
      Better to have questions you can’t answer than answers you can’t question

      Comment


      • RTT
        RTT commented
        Editing a comment
        Literally no pressure at all, so handle goes right to the handle bar as if no fluid whatsoever. So it seems to me no pressure in the line even from the master cylinder, so pumping from above has no effect.

        I had originally hoped the sticking and binding was just the lever, so I pulled the lever off, cleaned and replaced, but still binding. When I replaced the piston and seals, no more binding. So not sure what was up with that.

        Previous bike was a '96 Royal Star, so I would think a pretty similar setup, but maybe not. Never had problems bleeding the brakes, it seemed to always be a cinch. Not so here, it appears.

        Thanks for the reply! I will take a closer look at the t joint and banjo again.

    • #6
      I had the same problem you have the first time I replaced the fluid.
      What I found is; after you get most of the air out, then work the brake lever and let the lever snap back out, watch the reservoir and you will see tiny air bubbles coming up. When the air bubbles stop, snap the lever again, watch bubbles, repeat several times until air doesn't show any more. It works for me.

      Comment


      • RTT
        RTT commented
        Editing a comment
        Thanks for the reply... I tried that a few times, noticed the ever-so-tiny bubbles coming out. Didn't really let the lever snap back out. But maybe just needs a lot of patience tapping, flipping the lever, doing anything to force the air out. Maybe I'll just have to bring a beer out and watch those bubbles too, so long as I don't confuse the beer and the brake fluid. Wouldn't be good.

      • Duke
        Duke commented
        Editing a comment
        It does take time, so it's a good idea to relax and have a cold one.

    • #7
      Okay, problem resolved, thanks for all the suggestions.

      Turns out patience was key, I don't recall it ever being this much of a problem with previous bikes, but then again, I am the goof ball who couldn't get the oil drain bolt off my bike without a major problem coming up.

      In addition to patience, I had to throw out the vacuum pump and do it the old fashioned way.

      I am not sure if this made much of a difference, but I found that pumping the brake lever rapidly several times built up a small amount of pressure so that the brake lever wasn't going all the way to the handle bar. Then hold the lever, open and close, and a bunch of rapid pumping all over. I did this for a bit on the right caliper, then had my son come out and help me as I bled the left caliper, and got to the point where he could just squeeze once without pumping rapidly. I also tapped the T-joint, calipers and brake lines a few times with a small block of wood while he was pumping--may or may not have helped, but worth the try. Finally the brake lever got back to a normal squeezing action. Or at least normal for other bikes... normal for this bike had been binding and sticking.

      So now I can go back to proper trail braking without fear of dumping the bike on a clover leaf. Yay!

      Oddly, after I tightened everything and cleaned things up, I noticed an odd sound coming from the master cylinder... every time I squeezed the lever I would get a "wheezing" sound like mini bellows. Squeeze, squeak, release, squeak. Not a good sign. I tried isolating it... I thought maybe some leak at the banjo, maybe at the cover, maybe coming from the piston... after eliminating the banjo by putting my ear up next to it, and eliminating the cover as a source by taking it off (and sound was still there), it seemed to be the piston unit. "Oh shit" ran through my head. I can just see going through all this and one of the seals isn't in there quite right.

      But then it occurred to me maybe the dust boot wasn't sealing properly. So I twisted it around a bit, and probed with a small flathead screwdriver to make sure it was seated properly, and, sure enough, it was just the boot. Whew! I think air must have been wheezing in and out when I pulled the brake lever.

      So all is good now... at least momentarily. I now have a new tire to put on, and oil to change, and new brake pads on order.

      Thanks again, everyone!

      RTT

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