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Thread: R90S Bleeding Brakes

  1. #1
    Registered User
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    R90S Bleeding Brakes

    The bike is a 76 for which I have rebuilt the calipers and master cylinder. Also incorporated Stieger brake lines. Allowed the MC to become bubble free and bled each side until the fluid flow was bubble free. No resistance at the handle. Obviously I have missed something. Suggestions for what I should do next will be appreciated.

    rickt

  2. #2
    #4869 DennisDarrow's Avatar
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    Obviously you have an air bubble trapped someplace in the system.....hmmmm...lots of it. One "trick" is to lean the bike side to side as far as you can let it, do this several times, and then let it sit for a good little bit......God bless....Dennis

  3. #3
    Registered User STEVENRANKIN's Avatar
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    ATE Calipers adjustment

    Pardon if I put in two cents. I think there is an eccentric bolt on the ATE brake calipers found on the R90S bikes as well as my 78RS. If this bolt is not properly adjusted, as well as the system completely free of air and the cables adjusted to the master cylinder, the brakes will not work as well as they should.

    It has been a long time since I adjusted or bled a under the gas tank system with ATE brakes so I may be talking nonsense.

    Bless BMW for going to the better Brembo calipers and the handlebar mounted master cylinder system. There is a big difference in braking power and feel.

    I ride my 84 RT with the newer system and when I get on my ATE system 78RS, it is a few minutes of learning the ATE system has a bit less performance. St.

  4. #4
    Liaison 20774's Avatar
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    There could be a bubble of air trapped in the master cylinder. As the master cylinder sits on the frame, the front end is higher than the back end. This allows an area of air to lodge. Loosen the master cylinder and raise the back end enough to allow the air the migrate back so it can be pumped out through the lines as you bleed the brakes.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    Rally Rat 1074's Avatar
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    Also check the piston actuating pin with that little forked piece on the feeler gauge set to make sure that the piston is going back far enough to expose the fluid return port at the rear of the piston bore.
    Boxerbruce

  6. #6
    Get power bleeders

    Sent from my Nexus 6P using Tapatalk

  7. #7
    Quote Originally Posted by 20774 View Post
    There could be a bubble of air trapped in the master cylinder. As the master cylinder sits on the frame, the front end is higher than the back end. This allows an area of air to lodge. Loosen the master cylinder and raise the back end enough to allow the air the migrate back so it can be pumped out through the lines as you bleed the brakes.
    I've had this happen. The other method, not as safe as the above, is to loosen the brake line at the MC, place a wet towel under the connection (hell, cover every painted part in sight), and then crack the connection while squeezing the lever until a tiny amount of fluid comes out. Again, not as safe as the above but I can confirm it works.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

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