Airhead Rear Disc brakes

Discussion in 'Airheads' started by davemon, Apr 6, 2011.

  1. davemon

    davemon High Speed Airhead

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    I realize the brakes on the airhead leave a lot to be desired but anyone figured out how to make the rear disc on a 77 R100S work? Caliper change?
    Master cylinder change? Mine won't lock the rear wheel if I stood on it with both feet. Not really willing to go to drum but looking for a fix.
    #1
  2. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    77 R100S with a rear disc?

    The "S" bikes were manufactured with drum rear brakes.
    #2
  3. wirewrkr

    wirewrkr the thread-killer

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    Until 78.
    #3
  4. supershaft

    supershaft because I can

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    It is a REAL job to get all the air out of that system. I suspect that is your problem. That and/or a shot rubber line.
    #4
  5. Boxer Metal

    Boxer Metal Mad Scientist

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    It could have been made from 9/77-12/77. The only way to get the rear disc to work is a smaller bore master cylinder like a 12mm. Modify the mounting to use an earlier K100 with ABS, R1100 or R1150 rear brake master cylinder.
    #5
  6. Reryder

    Reryder Onward through the fog...

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    New brake hose is a must on these old Airheads. The originals have all swelled up and choked the hole down the centre by now.

    And that rear brake is a bitch to bleed for some reason. Taking caliper off and hanging it so rubber hose is vertical helps, as does a vacuum bleeder.

    Can't remember exactly but I think there were two sizes of master cyl bore, the later ones being smaller and more effective. You can get the old ones sleeved to fit the later piston/seal.
    #6
  7. supershaft

    supershaft because I can

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    Good advise you guys! Yea, the master cylinder bore is too big on those but still . . . the smaller MC's don't work well with junk lines full of air either! I really was going to say something about that but I though about first things first. :norton
    #7
  8. fishkens

    fishkens Long timer

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    I never liked the rear disc on my 78. Seemed like way too much crap not doing 1/2 what the drum could do. Plus it made getting the wheel off more difficult.

    But it sure looked good. :lol3
    #8
  9. Melrone

    Melrone Long timer

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    Had the same priblem with my 81 RT a few years back.I ended up replacing the master cylinder,new steel line,and a steel braided line to replace the rubber line.I then added a little wxtra line off the fluid resivoir so I could rise up above the master cylinder and then pumped the hell out of the pedal till I had a real brake..It was apain in the asss but it worked.Your right it does look good:deal
    #9
  10. Caddy82rats

    Caddy82rats Long timer

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    what have worked on my RS :
    I put old break pads, a crew driver between break pads.
    I pupm on break pedal
    Twist the larg flat screw driver, brake fluid and air goes back in brake fluid tank.
    I do again and again that
    #10
  11. davemon

    davemon High Speed Airhead

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    The bike is a 78 from the engine number
    I have replaced the rubber hose with a top grade one from a place in Ohio. New pads and bled the hell out of the system. Roughed up the rotors a bit with some emory cloth and cleaned out the cooling holes. So it looks like a rebuild of the master cylinder and getting the rotor turned
    #11
  12. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    Whats wrong with your rotor?
    #12
  13. boxerboy81

    boxerboy81 Stay Horizontal

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    Two mates of mine replaced their rear steel brake line and rubber hose with a custom one long stainless steel brake hose.

    Both are very happy with the solution. This comment was as significant for the rear brake as it was for the front.


    #13
  14. davemon

    davemon High Speed Airhead

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    The hose I put on was from Spiegler and the rotors are running straight but pretty polished.
    #14
  15. Boxer Metal

    Boxer Metal Mad Scientist

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    You can waste as much time and money and thought on this as you want. Unless you go to a smaller bore master cylinder nothing will really change. These things were crap when they were new.
    #15
  16. wirewrkr

    wirewrkr the thread-killer

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    That pretty much sums it up!
    #16
  17. Rapid Dog

    Rapid Dog bikes, booze, broads...

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    ..crappy as a dookati's I might add, even with a steel brakeline.
    Wished I had the drum brake off my '78.
    #17