Seized Brake Pistons - Solutions ?

Discussion in '1st & 2nd Generation 1983-1989' started by straycat, Nov 17, 2022.

  1. straycat

    straycat Member

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    Hi Fellas, a question for you guys re freeing up seized brake Calliper pistons.

    My Project CB900F, was left in a barn with no brake fluid in it, front callipers removed and rear one still on.

    both front a rear Master Cylinder are seized solid and will need replacing, the calliper pistons similarly seem to be seized.

    I suspect in all cases once the fluid is drained, what ever fluid is left in there, being hydroscopic, attracts moisture and then you get galvinic corrosion between the pistons and the calliper.

    Ive got them soaking in WD40, but im not hopeful in getting the pistons out even after that.

    Any other ideas on proven remedies out there ? or am I looking at new replacement callipers ?
     
  2. RogueRC24

    RogueRC24 New Member

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    If it was me (and nobody wants to be), I would probably try and used compressed air to get pistons out or some large jawed pliers and pull the pistons out. Then I would take the whole caliper to the sandblaster to try and remove corrosion. Then an air blowout followed by ultrasonic cleaning, alcohol cleaning, sanding if necessary (to smooth out any rough spots), and final cleaning to salvage the original parts. This is just me though and with the understanding that rebuild kits are available. - that was for the seized calipers.

    Master cylinders...haven't pulled one apart yet. sorry Stray. Possibly (with rebuild kit available), just ultra sound those suckers and see if you get movement back.
    I use dish soap for cleaning, nothing harsh to destroy o-rings and such.
     
  3. Thumbs

    Thumbs Member

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    The master cylinders should knock out after a few days soaking

    Calipers, I’d look for some others rather than struggle with little saving
     
  4. Captain 80s

    Captain 80s Member

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    I have a 1100 Shadow master cylinder (that I keep "bled") mounted on a piece of pipe just for this reason. I mount it in the vice and hook up my problem caliper. Pump them right out. Use a shim to keep one piston from popping out and before the other. You can get them right to the end and usually wiggle them with your fingers to release at that point. If not, compressed air will now be able to do it, when it wouldn't budge them "as delivered".

    Then I cap the hose with a bolt, crush washers and cap nut for the next shitty time. I've used it SO MANY TIMES. And it keeps the mess and caustic brake fluid away from the rest of the bike.
     
    Last edited: Nov 17, 2022
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  5. Captain 80s

    Captain 80s Member

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    With my aux master, I've popped a few calipers open I was sure were fucking toast. The pistons look new. Ultimately, it can depend on where the pistons were when they were sent to the bottom of the ocean for 10 years. Pushed mostly in, ups the success rate of finding decent pistons. The caliper bores themselves I can almost always clean up.

    I figure it's worth a few minutes of hooking them up to see what I really need to move forward. Maybe I only need two new pistons, instead of four.
     
  6. jstehman

    jstehman New Member

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    A grease gun has worked for me before.


    Sent from my SM-N950U using Tapatalk
     
  7. Captain 80s

    Captain 80s Member

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    Agreed. But I'd rather spray the calipers out with a little Brake Kleen when I'm done.
     
  8. straycat

    straycat Member

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    Cheers Guys, ill give that a try.

    I managed to get the 4 front pistons to move, hit them with WD40 inside and out, some heat and more WD40.

    I pushed them in just a wee bit with a big ass C-Clamp, ten used my piston pliers/grips to twist and rotate them. Theyre back soaking again now so that my just pop out with air or hookup to a MC as you suggest !!

    thanks again for the tips.
     
  9. raYzerman

    raYzerman Insider

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    I like the m/c idea rather than air... more control..... just leave the old pads in as a spacer to keep a piston from popping out before the others are out enough to work on. You got them moving, that's good news.
     
  10. straycat

    straycat Member

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    Fronts are out.

    Rear M/C may be functional so ill see if I can fill/bleed and use it to pop the rear pistons
     
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