Brake Caliper Piston Question

Discussion in 'Dyna Models' started by cmvsm, Nov 28, 2010.

  1. cmvsm

    cmvsm Member

    I recently went to change out my brake pads, and thought that I'd clean up the brake dust inside the caliper while I had the brake pads out. I gave a squeeze to the front brake to watch the pistons operate, and three seemed to go well, while there was one that seemed to move slower than the other three, it at all.

    I sprayed more cleaner and tried to clean around the piston which had some grime around it, but it seemed the more I messed with it, the less it moved. I did the cleaning a couple of times, while pressing the pistons back into the caliper each time, to see if I was breaking up any of the gunk. I had the brake fluid resevoir cap off, and of course, fluid was coming out.

    I went ahead and put it all back together, topped off the brake fluid, and squeezed the brake until I had pressure again. Put it in neutral and the new pads seem to be grabbing as expected. It was the end of the day, so didn't take it out on the road, but rocking back and forth in the garage.

    I guess my question is in regard to that piston. Is it possible that after I put it all back together again, topped off with fluid, that the pistons don't have to travel all that far with the new pads and don't worry about them? Or should I perhaps look at a rebuild kit and tear it apart if the piston is indeed stuck. Seemed like it was operating just ok when I opened it up, as all pistons were relatively out in equal length. It was only after I began cleaning, losing fluid, and pushing them in that they started going cockeyed. I've got 28K on the bike, and not sure when the last service on the brakes were done, but the pads definitely needed replacing. They were worn a bit uneven on one side.

    Obviously, just don't want to have any issues. Thoughts? Thanks.
  2. TripleJ

    TripleJ Senior Member

    Chances are your brakes will be fine. It does not surprise me that one piston was slower to move than the others for the same same reason that water will take the path of least resistance. If the other pistons moved more freely the fourth piston would not move until something caused the other pistons to meet with resistance.

    Also the more you cleaned the piston that was not moving the drier it became as you pushed it back into the caliper possibly making it even harder for it to move.

    I would ride it and keep an eye on the brakes for any problems to arise but would not tear it apart at this point.
  3. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    I don't believe in messing around with the brakes. If you are even the least bit concerned about them, rebuild them. Brake failure is not an option, especially the front!!

  4. jaxdwg

    jaxdwg Active Member

    I agree with TripleJ. If the brakes are working and not leaking, the fact that one is a bit slower than the others is not a problem as long as it's not actually sticking, which, it sounds like, it's not after you pumped it back up and all the pistons made contact with the pads.
  5. cmvsm

    cmvsm Member

    Thanks for the replies everyone. I just looked at them again while engaged on the bike. On the first side, I can see the pistons with a light, they are out equally when compared to each other, and look well engaged. If both sides looked like this, I'd be good to go.

    On the other (second) side, the first piston is a little more recessed when compared to the first side, but still looks 'ok' I suppose. The second piston on the second side, I can see the chrome of the piston, but it is even more recessed than the one next to it, almost to the point where it is flat. I believe that this is the one that I was worried about to begin with.

    The chrome on the caliper itself is pretty pitted and doesn't look that great. Now would be the time to replace I suppose, but hard to part with the 350 bills right now.

    Anyone know what a rebuild kit would cost with pistons from Harley? Thanks again.

    NEWHD74FAN Experienced Member Retired Moderators

    A rebuild kit is not that expensive, $65 or so...problem is you said that you could see pitting in the caliper...was this anywhere around the piston area in question. While in some old time cast iron type you could do a "touch up" of the bores or knurlize them, the modern aluminum alloy designs do not allow for this.

    I would try rebuilding the caliper in question, and if the damage is more than "skin deep" that simple crocus cloth will not clean up...a new caliper body is in order. Brakes as TQ said is not something to mess with...and the key is prevention, changing fluid every year or two is not a bad idea if you use DOT3 or 4 which attracts moisture and if left in your braking system CAUSES that corrosion you are dealing with.
  7. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    Im another that would not use a bike if the brakes were suspect they might be ok during normal riding but when you get in an emergency situation you need 100% braking efficiency and not 75% at best
    ill amend smittys favourite saying your life you decide

    i would rebuild or replace the calliper

  8. Jonas

    Jonas Junior Member

    If you did not try this when cleaning the pistons. Before you rebuild anything try it. To really clean the pistons they need to pumped out "almost" all the way.

    With the caliper off hold two of the pistons(that move easy) in with an old pad. You can probably hold them with your hand, Then pump the two out including the slow one. Clean it as it comes out. You need to get that piston pumped "almost" out and clean all around it. You might have to hold the three that move easy to get the stuck one cleaned. Repeat until they all move the same.
  9. cmvsm

    cmvsm Member

    Thanks Jonas. I actually did that and the one would still not move. The one next to it was moving a little, but not much. I'm going to take fins advice and go ahead and replace the caliper since it is so pitted. I can get a re-chromed, re-built one for about $200, which I can swallow. Worrying about the brakes kind of takes the fun out of riding...:D
  10. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    Excellent idea! Good move.