Master cylinder

Discussion in 'Wheels' started by jachey, Aug 26, 2012.

  1. jachey

    jachey Member

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    When front brakes are applied on first pull the handle come mostly all the way back to the grip. After a pump or two I get a good pull as it should. I bleed the brakes multiple time with no improvement. There are no leaks or fluid loss. I am thinking the master cylinder is shot, is this correct? 01 Ultra classic
     
  2. Hoople

    Hoople Account Removed

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    Once the lever has built up, can you keep high applied pressure without any bleed down.
    You didn't say how you got to this point. Everything was fine, then one day the lever needed more travel? You opened the system to replace pads or something and now you have more lever travel?
     
  3. Webbtron

    Webbtron Banned

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    On My 2000 RKC I had to remove the caliphers and turn them to get te air to the bleed screw. This was the first time I had done the fluid on this bike and I believe I could have done a better job of draining the old stuff, thus not getting so much air in. Before that I tried all the cool tricks in the self help, which worked to a degree but never got the lever to where I wanted it. Lastly this was more of a spongy feel than a complete collapse of the handle. So your case might be the master cylinder.
     
  4. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    I've had this problem in the past and tried most of the tricks at one time or another. They didnt work on mine. What did work, was to remove the calipers one at a time, remove the pads, use a small block of wood or paint stir stick to clamp one side of the caliper pistons in place with a C-clamp. Then carefully pump brakes until the un-clamped pistons protrude until you see clean piston. NOT too far the piston will come out of the bore and make a brake fluid mess. Now remove the lid on the masrter cylinder and slowly by hand push each piston back in. continue to do this for each pair of pistons. Keep in mind that you have to put the master cylinder cover back on to pump out the next pair of pistons. I guarantee that at some point in the process you will get a BIG bubble of air to escape through the master cylinder. I would also bet that it will come from one of the top pistons where air gets trapped and cant escape without force.
    While your in there you may as well get an old toothbrush and brush the sides of the pistons clean with some clean brake fluid. Clean the pins and use some brake grease on them during re-assembly.
    Let us know how you make out.
     
  5. jachey

    jachey Member

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    I didn't do anything to the system at all. It just slowly over a few rides started to give more travel. The bike did sit 3 years and I was told by the previous owner that they had the bike serviced at their dealer due to a stuck front caliper. When I bought it this year it was working fine. After I pump the brake lever it does hold with no leak down.
     
  6. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    Probably wouldnt hurt to change the brake fluid and clean the brakes up. If you have a mighty vac brake tool, you can change the fluid out pretty quickly. Look at my post above, this will bring your lever feel back to normal.
     
  7. jachey

    jachey Member

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    Thank you all for your help. Hopefully I can get some time this week to get to work on it.
     
  8. lordharold

    lordharold Active Member

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    if you take an old brake line and pinch it off and or same size bolt and install it into the master cylinder then try and see if your lever builds and holds pressure you can tell if it is the master cylinder or the brake calipers that are giving you the problem.
     
  9. Jack Klarich

    Jack Klarich Expert Member

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    The master cylinder is by passing, you can rebuild it or replace it, H D sometimes takes the plunger apart and stretches the spring, band aid on a broken leg, Don't take chances with brakes, My experience with brakes it is not worth it
     
  10. RibEye

    RibEye Junior Member Contributor

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    I had the same problem with my '03 RKC. It had also sat for a couple years.

    I rebuilt the MC, using the HD rebuild kit. That helped a small amount, but not tremendously.

    I fixed it definitively. Here is what I learned:

    If when you start the day, you have to pump it a few times to get the pads to the discs, but when you do get the pads there, they do not feel mushy or soft, rather, nice and hard at the contact point, you may have my problem.

    If when you get to the contact point, and the brakes feel soft or mushy, you may have air in the system. Air tends to compress, fluid does not.

    Now for my fix. I find that HD pads are chirpy and dusty. The dust gets in to the brake mechanism, and if allowed to sit, it could accumulate and bake a little bit, making a sort of crust on the pistons. The brakes do not have return springs. They depend on just a bit of eccentricity in the discs to push the pads off when not engaged. Normally, they will not push off very far, and will even kind of contact during normall operation, giving that chip-chip-chip sound that goes away when lightly applying the brakes.

    Now, if for some reason, the pads get moved back too far from the discs, it takes more fluid to move them back up against the discs, like what happens when you pump. Once up against the discs, braking is positive and strong. How this happens is, if you have crust on the pistons, and the rubber seals around the pistons may hang up on this crust. The seals will stretch a bit, and allow the pads to move up to the contact point, but over a short time time the seals will drag the pads back in, and too far, and push fluid back up into the MC that normally would stay in the lines and calipers (staying in the lines and calipers and is how they auto-adjust for wear).

    OK. With all of that being said, do as Bodeen said, and carefully extend the pads out so you can access the pistons. clean off those pistons with shoe laces and brake cleaner, till they are clean and polished again. Reinstall your calipers and test. You just may be good to go once again.

    Just an idea, and it fixed me all up. Maybe you too.

    Good luck,
    Rich P