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Thread: '84 RS forks question

  1. #1
    Registered User ezwicky's Avatar
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    '84 RS forks question

    When I disassembled the '84 forks with Brembo brakes on my 1980 R100RS barn find, there was nothing in the sliders to fall out. No spacers or bumpers or anything.

    The fork internals look as they should, maybe the sliders are as they should be too, but from the fiche it's really hard to tell because there seem to be a lot of extra pieces that I didn't have, and are not clear in the descriptions about what year they should be for.

    Aside from the seals, boots and felt, the only thing in the sliders is the flat disk at the very bottom that appears to be held in place by a snap ring. The disck has a threaded hole for the fork oil drain plug, and a larger hole for the allen bolt that screws into the fork internal assembly.

    Is something missing, or am I good to go?

    Thanks in advance,

    Eric
    Last edited by ezwicky; 06-03-2021 at 04:29 PM.
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  2. #2
    Registered User STEVENRANKIN's Avatar
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    Oh man

    Oh man, I had my brembo forks apart over the winter and so I may be way off but I believe you are OKAY to go. I am turning it over in my mind trying to dig up the memory of what came apart when I removed the sliders to have them powder coated, I don't remember any bumpers.

    1980 was kind of the cross over in systems for the RS. I stated in my response to the brake cover changes were in effect in 81. I should keep out of it and point you in the direction of snowbum's website, Anton Largidare, Brook Reams or anyone else but me. St.

  3. #3
    Registered User ezwicky's Avatar
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    Thanks Steven. The bike had '84 forks on it, with the original '80 forks with ATE calipers included as spares. I'm sticking with the '84 / Brembo, and going to a handlebar-mounted master cylinder.

    When you had the sliders off, do you remember removing that snap-ring that seems to hold the bottom disc on?

    Brook's site is the first place I looked, but it's still not clear. I asked Tom Cutter yesterday but have not seen a reply yet.
    Last edited by ezwicky; 06-04-2021 at 11:36 AM. Reason: typo
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  4. #4
    Registered User STEVENRANKIN's Avatar
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    Snap ring

    No, I didn't remove the snap ring. I was able to clean things out well enough without doing it. One less thing to have go wrong, a flying snap ring sailing off into the nether lands of my garage. LOL, St.

  5. #5
    Registered User ezwicky's Avatar
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    Mine are almost welded on with rust. After days of repeated PB Blaster / heat / tapping I was able to remove one ring, but the disc itself seems immobile. The other slider, the ring is still resolute in its refusal to budge. I wonder why I even am doing it but the fact that they are so rusted there makes me think it's just good practice to at least renew the rings.
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  6. #6
    Registered User STEVENRANKIN's Avatar
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    Depends

    If they are as rusted and crusty as you say, I would have in the same circumstances might have removed mine.

    I would caution you to make sure you can get replacement parts from somewhere just in case they are too far gone to reuse. Who knows what you will find if you do get them out. Thank goodness there is no rubber o-ring involved to crap out and need replacement, that would be a BMW joke. Good luck, St.

  7. #7
    Registered User ezwicky's Avatar
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    Snowbum's front suspension page has a diagram that shows no bumpers, and labels the disc at the bottom of the slider as "slider base". I suspect that it's removeable in case thge drain plug hole threads get stripped. I'm just going to replace the snap rings / circlips and leave well-enough alone after that.
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  8. #8
    Registered User jad01's Avatar
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    Mine had the spacers in the bottom when I replaced the seals last year. One was somewhat stuck in there, so it wasn't obvious at first. Maybe a prior owner removed them on yours?
    Jim (MOA 83200)
    '78 R80/7 (Anastasia) and '84 R100RS (The Millennium Falcon), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  9. #9
    Registered User ezwicky's Avatar
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    Quote Originally Posted by jad01 View Post
    Mine had the spacers in the bottom when I replaced the seals last year. One was somewhat stuck in there, so it wasn't obvious at first. Maybe a prior owner removed them on yours?

    Thanks Jim. You reference the same diagram I saw on Snowbum's site, and the red arrows you added point to the slider base, o-ring and circlip (I didn't know there was an o-ring in there... I bet mine are toast because of all the heat and PB Blaster...

    I see the spacer you (and Brook Reams) mentioned. So it does indeed look like a previous mechanic omitted to include them at rebuild time.

    Now I am going to have to get that slider base out so I can replace the o-ring. Hopefully I can find the spacer on the fiche and it's still orderable.

    EDIT: RealOEM shows no o-ring, but this part #20, which I ordered along with the circlips:

    https://www.realoem.com/bmw/enUS/sho...diagId=31_0316

    BTW what color is your RS? I really like that shade of blue. I'll be taking my bodywork and tank to the painter next week and I need to decide on a color. I'll let my wife assist in the selection, it will be fun for her. But I want to show her some representative samples, so I'll let her have a look at your pics.

    Here's my slider bottoms and fork internals at the moment:

    IMG_1584.jpg
    IMG_1585.jpg
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  10. #10
    Registered User jad01's Avatar
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    Quote Originally Posted by ezwicky View Post
    Thanks Jim. You reference the same diagram I saw on Snowbum's site, and the red arrows you added point to the slider base, o-ring and circlip (I didn't know there was an o-ring in there... I bet mine are toast because of all the heat and PB Blaster...

    I see the spacer you (and Brook Reams) mentioned. So it does indeed look like a previous mechanic omitted to include them at rebuild time.

    Now I am going to have to get that slider base out so I can replace the o-ring. Hopefully I can find the spacer on the fiche and it's still orderable.

    EDIT: RealOEM shows no o-ring, but this part #20, which I ordered along with the circlips:

    https://www.realoem.com/bmw/enUS/sho...diagId=31_0316

    BTW what color is your RS? I really like that shade of blue. I'll be taking my bodywork and tank to the painter next week and I need to decide on a color. I'll let my wife assist in the selection, it will be fun for her. But I want to show her some representative samples, so I'll let her have a look at your pics.

    Here's my slider bottoms and fork internals at the moment:
    Hi Eric,
    I hope that o-ring replacement goes well. Please document it here when you do it- I didn't find much on it in my search, so I'm sure it will help someone else down the road (maybe me!) when they are looking to disassemble and replace theirs.

    That paint is the original code for that bike: Alaska blue metallic (542) with silver pinstripe (134). My local painter uses BASF paint, which owns Glasurit. They did nice work- I'm really happy with it.
    Jim (MOA 83200)
    '78 R80/7 (Anastasia) and '84 R100RS (The Millennium Falcon), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  11. #11
    Registered User ezwicky's Avatar
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    Quote Originally Posted by jad01 View Post
    Hi Eric,
    I hope that o-ring replacement goes well. Please document it here when you do it- I didn't find much on it in my search, so I'm sure it will help someone else down the road (maybe me!) when they are looking to disassemble and replace theirs.
    I am really frustrated with trying to get the circlip off the other fork slider. The first one was hard enough but this on seems almost welded in.

    And on the one that I did get the circlip off of, the slider base will not budge. I don't want to ruin the sliders, but I also want to make sure what should come off *can* come off

    Thanks for the paint specs!
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  12. #12
    Registered User STEVENRANKIN's Avatar
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    Maybe

    Not to be a jerk but in the now third major overhaul of my 84RT and the previous two I never bothered to remove the snap ring or the bottom of the fork sliders, there was never any leaks. If you go to Brook Ream's website where he is restoring a similar bike, he also makes a point he did not remove these parts.

    Maybe the difficulty of getting things apart is a warning some things might be best left alone. I have had my fork sliders cleaned, bead blasted, powder coated twice now and as I said never had those parts apart or had a leak because they were not taken apart.

    In my search of the BMW microfiches, I really don't see any O-ring listed or even the snap ring for this. The fork slider is sold as one piece.

    Sorry, this is my two cents, I myself don't like making more work or opening a bundle of snakes unless I absolutely have to. Good luck with things. St.

  13. #13
    Registered User ezwicky's Avatar
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    I agree Steven. I just worry now that *if* there is an O-ring, maybe I corrupted it my heat and PB Blaster cycles. The when I put it back together I could have a leak.
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

  14. #14
    Quote Originally Posted by ezwicky View Post
    I agree Steven. I just worry now that *if* there is an O-ring, maybe I corrupted it my heat and PB Blaster cycles. The when I put it back together I could have a leak.
    Put some oil in the slider, set it upright on some paper towel or a shop towel and see if it leaks. That won't be pressurized but will be a good first test.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  15. #15
    Registered User ezwicky's Avatar
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    Quote Originally Posted by PGlaves View Post
    Put some oil in the slider, set it upright on some paper towel or a shop towel and see if it leaks. That won't be pressurized but will be a good first test.
    It will leak out the bottom hole where the large allen bolt screws into the fork internals. But I *could* just put it all together for testing purposes. I will do that this afternoon. Thanks.
    BMWMOA #182796

    '76 R90/6
    '80 R100RS restoration project

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