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Is my caliper salvageable?

Discussion in 'XJ Technical Chat' started by jag3, Oct 30, 2020.

  1. jag3

    jag3 Member

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    I'm in the middle of rebuilding everything and onto rebuilding the calipers. Is my caliper history? I noticed what looks to be a scratch going half way around where the piston goes in, I can barely feel it but can with my fingernail. Is this a problem and do I need a new caliper? I also have them stripped down to repaint. Any suggestions on what I need to do on the scratch? Can I leave it? Does it need to be honed, can it be and won't that increase the bore size? Thanks for all the advise. I can't get the seal guides any better. Do they look ok?
    20201030_175631.jpg 20201030_154957.jpg 20201030_190630.jpg
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    Oh dear , those look pretty bad, but you could get a dowel rod the same size as piston cut about 3" in length ,wrap some 400 grit sand paper around down . Work it back and forth till the scratches are cleaned up , may take awhile , keep changing the paper , you can keep it wet . If you want to speed it up still a hole in Dowl rod put a sheetmetal or wood screw in dowl check in a drill ,run it several times till scratches are worked out .
     
  3. Toomanybikes

    Toomanybikes Well-Known Member

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    Have seen that a few times, but as long as the scratch does not impede the piston sliding in and out of the bore it should not be a problem. Polish it with some 600 wet sandpaper to clean up the surface.
     
  4. JBurch

    JBurch Active Member

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    What does the piston look like? The piston does not "ride" on the bore of the housing; while it (the bore) looks "bad" it is of little consequence. The piston "rides" on the "o" ring, so long as the piston has no nicks, or scratches, you are good to go.
     
  5. Timbox

    Timbox Well-Known Member

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    The puck and the "O" ring surface are what holds back the fluid from coming out. Sure the more room there is between the side of the puck and the caliper. Sanding the caliper surface that the puck rides along will do no good, it will only make the distance between the puck and the wall greater and allow more fluid between the puck and the caliper wall. imho.

    Having the puck it self be mirror smooth and free from scratches for that it mates well with the "O" ring from the rebuild kit will keep it from leaking and function as it should. Can you show us what the puck looks like? If they are in good condition I think you can make those work just fine.
     
  6. jag3

    jag3 Member

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    This is what the pistons look like. The one on the left and pictured by itself are from the caliper pictured and the piston on the right is from my other caliper. Pictured are the bad spots. Thank you everyone for your help.
    20201031_121414.jpg 20201031_121510.jpg
     
  7. JPaganel

    JPaganel Well-Known Member

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    That's not "OMG terrible", but still kinda bad.

    Old Yamaha brake pistons are made of fairly soft steel and chromed. Nicks in the chrome lead to leaks and eventually to rust. There are people out there making them out of stainless steel, I bought some for my old XS, they are probably still fine 10 years later. Check ebay - lots of them sell their stuff there.

    Your caliper is most likely fine. The important part in it is not the bore, but the grooves where the seals sit. Use a small brass brush to clean them out, but don't get carried away with a Dremel.
     
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  8. jag3

    jag3 Member

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    Thanks. I've tried cleaning the seal grooves with a wire brass brush and cant seen to get them any better.
     
  9. Minimutly

    Minimutly Well-Known Member

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    New chrome pistons are cheap. There is nothing wrong with your calliper - that's a machining mark, it's been there 40 yrs...
     
  10. JBurch

    JBurch Active Member

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    What are you using for solvent? I prefer CRC "Brake-clean", works as well as anything else I have used; Auto-Zone.
     
  11. jag3

    jag3 Member

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    I soaked them in Gunk Parts Cleaner (CC3K) and then both 3M High Power Brake Cleaner and CRC Brake-clean. Thanks for the responses on the calipers, I'll be ordering a new pair of pistons.
     
  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Use a dental pick to clean out the grooves.
     

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