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Thread: R90S Front brake rebuild video?

  1. #1
    Registered User ebeeby's Avatar
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    R90S Front brake rebuild video?

    Anyone have a link to a rebuild video for the R90S from brake system? I have a weeping caliper on a 20 year old rebuild. Good clean brake fluid. Probably just time for seals.
    But I do not understand adjusting the concentric on these calipers after a seal rebuild and new pads.
    1973 R75/5
    1975 R90S

  2. #2
    Registered User STEVENRANKIN's Avatar
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    Same

    This is Brook's site, he has the best videos and descriptions. Same system on the R90S. St.

    https://brook.reams.me/bmw-motorcycl...ster-cylinder/

  3. #3
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    Quote Originally Posted by ebeeby View Post
    But I do not understand adjusting the concentric on these calipers after a seal rebuild and new pads.
    I should do a video on this. I have the best method for brake pads with the rotor.
    Ray Puckett, MOA #225597
    IBA #82538
    '74 R90/6. '75 R90S. '76 R90S. 2019 R1250RT.
    Too many dirt bikes.

  4. #4
    Registered User ebeeby's Avatar
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    Quote Originally Posted by craydds View Post
    I should do a video on this. I have the best method for brake pads with the rotor.
    Please do!
    1973 R75/5
    1975 R90S

  5. #5
    Liaison 20774's Avatar
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    I've read about the process of using a Sharpie to put radial marks on the rotor. Then when spinning the tire and applying the brakes you look at how the pads erase the marks on the rotor. The idea is you wanted to evenly erase the marks. Make adjustments of the eccentric and try again.

    I was never able to make that work well. I heard about a different approach. Basically, I apply a small amount of brake pressure and then turn the eccentric one way until I feel resistance, then back the other direction to find resistance. I can then figure out where the center is when the pads are parallel to the rotor. I can then put the cap back on the eccentric.

    The last thing I do is to use a bungee or something to hold the brake lever pushing the pads on the rotor overnight. This helps to allow the air bubbles to work their way out of the system. Check in the AM for decent lever movement and good response.
    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!

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    Quote Originally Posted by 20774 View Post
    Basically, I apply a small amount of brake pressure and then turn the eccentric one way until I feel resistance, then back the other direction to find resistance. I can then figure out where the center is when the pads are parallel to the rotor.
    This, precisely, is the correct technique. Now, if I can make a really bad video demonstration, I will post it here.
    Ray Puckett, MOA #225597
    IBA #82538
    '74 R90/6. '75 R90S. '76 R90S. 2019 R1250RT.
    Too many dirt bikes.

  7. #7
    Quote Originally Posted by ebeeby View Post
    Anyone have a link to a rebuild video for the R90S from brake system? I have a weeping caliper on a 20 year old rebuild. Good clean brake fluid. Probably just time for seals.
    But I do not understand adjusting the concentric on these calipers after a seal rebuild and new pads.
    The eccentric pin rotates the caliper(s) so the piston side pad is perfectly aligned with the rotor. That ensure that the total area of the pads are squeezed against the rotor.

    Having had my R90s for over forty years, I like to visually verify alignment and the insert a feeler gauge between the pad and rotor to verify the pad has the same clearance, and is thus aligned.

    And, you can remove one of the fork axle pinch bolts to insert into the adjusting pin, (rotating clockwise obviously). When you need to remove the bolt, just apply lever pressure and back the bolt out.

    When aligned/adjusted, the brakes are pretty effective IMHO. Nothing like my '04 RT servo assisted brakes, but decent nonetheless.

  8. #8
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    Quote Originally Posted by RPGR90s View Post
    The eccentric pin rotates the caliper(s) so the piston side pad is perfectly aligned with the rotor.
    Actually, you want the inside pad (wheel side) perfectly aligned/flat/flush with the rotor. The inside pad is fixed/immovable and must fit flat against the rotor. The outside pad (piston side) is somewhat "flexible" in that it will self-align to the fixed inside pad. Kurt's alignment procedure described above is the easiest and best way to to adjust the caliper.
    Last edited by craydds; 12-01-2022 at 09:29 PM.
    Ray Puckett, MOA #225597
    IBA #82538
    '74 R90/6. '75 R90S. '76 R90S. 2019 R1250RT.
    Too many dirt bikes.

  9. #9
    Quote Originally Posted by craydds View Post
    Actually, you want the inside pad (wheel side) perfectly aligned/flat/flush with the rotor. The inside pad is fixed/immovable and must fit flat against the rotor. The outside pad (piston side) is somewhat "flexible" in that it will self-align to the fixed inside pad. Kurt's alignment procedure described above is the easiest and best way to to adjust the caliper.
    you're absolutely right. Wasn't thinking clearly even though I've done this a million times.

    Thanks for the correction.

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