Improving ATE brake feel on '74 bikes

Discussion in 'Airheads' started by inigoj, Oct 21, 2017.

  1. inigoj

    inigoj Adventurer

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    Hey all,

    I am in the process of reassembling my '74 R90S. Previously I have tried upgrading the brakes on my '76 by fitting a bar mounted M/C from a later bike to good effect. I would like to do the same for the '74 as it will be ridden regularly (and quickly).

    Has anyone tried to build a better solution that keeps the /5 style controls? I was thinking you could possibly mount a separate bar mounted M/C with a rod or shorter cable to connect it to the lever. Still not ideal but better than what they regularly have i guess.

    7_closeups.jpg

    Hope this made some sense.

    Thanks,
    Inigo
    #1
  2. bmwrench

    bmwrench Long timer Supporter

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    I think Johnny Cash (an inmate here, not the singer) found a solution to this.
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  3. blaine.hale

    blaine.hale Long timer

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    To be honest, it's an expensive venture involving adapting later forks and later hand controls. I'm more prone to saying if you want a better stopping and performing bike, buy one. If you want to ride an old BMW, set your expectations and adjust your riding style accordingly.
    That said, there are minor improvements. Stainless lines, modern pads, caliper rebuild and different sized pistons for the MC.
    #3
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  4. JakobDK

    JakobDK Been here awhile

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    21740046_10211598642454128_1506928066738672627_n.jpg 21731058_10211598643014142_7825323636838527630_n.jpg Skærmbillede 2017-09-15 kl. 15.07.41.png
    Saw this on a Facebook page for Airheads.
    #4
  5. nobbylon

    nobbylon Long timer

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    I was going to do the same conversion on mine but losing the old levers was not an option for me. I like the clean original look to the bike.
    Stainless hoses, a good bleed and most important, correct setting up of the calipers.
    After uncrewing the pivot pin cover I set the pads parallel and then while holding the brake on I replace the spring and cover. This stops the chance of turning the pivot pin when tightening the cover.
    My twin disc 90s has always felt adequately braked. The single disc 75/6 I have could really do with an extra disc even after the set up and stainless.
    #5
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  6. OdyBandit

    OdyBandit Long timer

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    Just wondering if drilled discs would make a difference on the 74’s?
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  7. Jim K in PA

    Jim K in PA Long timer Supporter

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    An effective and least invasive alternative is to convert your UTMC to a 14mm unit from a solo disk bike. You will need a splitter or have another hole drilled and tapped in the MC.

    Start with the proper fettling of the calipers and a good set of pads. I still have the 17mm master on my '79 dual ATE setup and it works fine. However, my perspective is an anomaly in this neighborhood.
    #7
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  8. Brun

    Brun Been here awhile

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  9. chasbmw

    chasbmw Long timer

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    The smaller the MC the better, 14mm would be adequate on a twin disc bike13mm better. With Norton’s there are companies such as RGM who will resleeve the MC to 13mm, don’t know if anyone does that for BMWs.


    Sent from my iPhone using Tapatalk
    #9
  10. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    FWIW, I have a set of (lower) front forks for dual disk brakes with the 14mm axle suitable for a R90 that I don't need. I bought them on my journey for dual disk front brakes without complete knowledge of the subtle differences in years and models. However, I'm not certain these (lower) forks are suitable for the 90S.
    #10
  11. Renner

    Renner combustophile Supporter

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    +1
    I've done this for a R100/7 twin disc set-up.
    My '74 R90S's master cylinder had pitting so I had that sleeved to 14mm, Mark Frappier performing the work. (I understand Whitepost sends work to him as well.)
    Great results on both counts.
    #11
  12. Interstatement

    Interstatement Been here awhile

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    I'm doing the JonnyCash-style mod (as per the link Brun shared) on my R75/5, but with a new, as yet unproven but seemingly sound, twist. Trimmed original perch as in said link, but instead of the new 13mm Magura, I plan on using a 15mm MC and lever from a Moto Guzzi Convert, circa 1976. The round fluid reservoir looks a bit more 1970's-apropos and the lever itself is a dead ringer for the original BMW part, smooth curve, slight finger detents, and all! Pardon the terrible image, it was all I could find at the moment. The one caveat I will put out there is that the OE "S" bars may not have enough of a straight grip area to fit all of this. Brun solved this by fabbing some short extensions, I'm skirting the problem by using sidecar bars with a similar rise to the S bar (albeit with a bit less pullback) and much more straight grip area. My original plan was to lop off the ends once the new parts are installed as far in as they could go, but I've run the bars at full width for the past year on a drum brake /5 and I've grown to like the width. YMMV with an S fairing.

    191406580401_1.jpg
    #12
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  13. Voltaire

    Voltaire Titanium and Ceramic Hipster

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    I had my R90s sleeved down, ss lines, ss pistons, and a nice set of semi floating Speigler discs. works for me.
    Saying that the speed limit here is 60 MPH and we only have about about 100 of motorway.

    I have the same set up on the racebike but with a 13mm Brembo M/C and its better but you need to use the rear a lot compared to the racebike with the brembos.
    #13
  14. Wirespokes

    Wirespokes Beemerholics Anonymous

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    The 14mm undertank master works just fine because it's got an extra lever operating the piston other than the hand lever. It's like having an extra long hand lever. If you don't want to modify the controls or replace them, that's the way to go. I've done that to my dual disc airheads and the improvement is quite noticeable.
    #14
  15. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    One thing to consider before going on, what can be a long an uncertain journey, is to adjust the brake cable - and replace it if it's not recent. Adjustment of that cable allows getting a better purchase or grip on the brake lever. I wore out a set of brake pads in ~7k miles that way and the braking was improved. Is it same benefit of a handle bar MC or dual disks? No, but it's an improvement IMO (a firm grip is still needed).

    Also, and not to redirect the tread, but proper adjustment of the ATE brake caliper eccentric pivot is important.
    #15
  16. danedg

    danedg Horizontally Opposed

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    The best improvement by far on the OEM ATE's that I've found was replacing the old hoses with fresh Speiglers.
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  17. Kiwiabbo

    Kiwiabbo Long timer

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    Got both versions and the handle bar mod is by far and away the best mod to the brakes. So either upgrade existing with better discs, lines and pads or go whole hog and change to bar mounted MC. It’s only braking...I mean who really needs it. If you going to be using it all the time I know what I would be doing. DCBFDA0F-CFEA-4CC3-B392-7AB93BFFEA6A.jpeg
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  18. bentombed

    bentombed Been here awhile

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    came here to say this - all the guys running UTMC i know get them resleeved to 13mm and then get the MC pin ground down to fit. I have tried it and the result feels like modern brakes.
    #18
  19. Wirespokes

    Wirespokes Beemerholics Anonymous

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    The 14mm is stock for the Under Tank Master. Give us more detail on the piston and seals. What rebuild kit did you use?
    #19
  20. bentombed

    bentombed Been here awhile

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    HI - no kit - what these guys did was to re-sleeve the twin disc down master cylinder to 13 mm. The next step was to put the master-cylinder pin onto a lathe and grind that down to fit the new sleeve. At that size you can apparently use regular o-rings to seal it all up. The reduced cylinder size gives massive improvement in brake responsiveness and feel. I rode around briefly on a bike with this done, two finger brakes with the ATE undertank set up. amazing.

    I learned all this after i did my handlebar conversion, was told it was an old race trick. I will get more details on the process and post them up.
    #20
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