Improving ATE brake feel on '74 bikes

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

  1. black knight

    black knight Long timer Supporter

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    my 1974 Type IV fork exchange updated to 12.5'' HD rotors , carriers, dishes, brake lines, flex brake lines, new caliper carriers custom made, 4 pot brembos, under tank master......... two finger operation

    cost about the half of what the fuk'n bike is worth

    next time install a GSXR fork conversion ......
    would be MUCH cheaper.
    https://cognitomoto.com

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    type IV not II

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    #41
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  2. Jim K in PA

    Jim K in PA Long timer Supporter

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    Harry - Nice work. What HD were the rotors from? Did you have to machine the window to fit the BMW hat (carrier)? I found Triumph 900TT rotors c2001 fit up to the BMW rotor hat pretty good, just have to drill the mounting holes.
    #42
  3. black knight

    black knight Long timer Supporter

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    thx

    rotors from j&p cycles and we bought the ones with the most meat at the center so when we machined the centers to fit the carriers. we also needed the largest dia. rotors we could find to keep the calipers as far away from centerline

    ALL BECAUSE I wanted to keep my spoke wheels. we needed the spoke clearance and when you look we just clear the spokes. i have 3/16'' clearance to remove the wheel after removing a caliper to fix a flat if needed .

    everything and i mean Everything was touched by a lathe / mill...... was machined to fit ....... very $$ / time at a mill
    #43
  4. garandman

    garandman Wandering Minstrel

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    I am sending myR90/6 master cylinder to Apple Hydraulics.
    #44
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  5. garandman

    garandman Wandering Minstrel

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    Testing braking with modified master cylinder today.
    #45
  6. ysrebob

    ysrebob yessiree, Bob.

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    Garandman, how did it turn out?

    Getting ready to try the same kinds of things with a 1975 Slash 6... as it stands, my little girl’s bicycle with a rear coaster brake can probably stop harder than the airhead. Cost of going to dual discs looks prohibitive.
    #46
  7. Kiwiabbo

    Kiwiabbo Long timer

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    I think getting the pads set up correctly and good pads makes a big difference for a start.
    #47
  8. garandman

    garandman Wandering Minstrel

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    A lot better. Still at shop, getting an electronic ignition installed.
    #48
  9. mattcfish

    mattcfish R90X Supporter

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    Fabulous, what mill are you using?
    #49
  10. Jodon

    Jodon Been here awhile

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    Garandman, so you got it sleeved down to 13mm?
    What if any was the modification re mc piston/seals?
    And does anyone know of a source for the little rod between the mc actuating arm and piston?
    NLA everywhere I've looked.
    #50
  11. chasbmw

    chasbmw Long timer

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    I totally agree, my 13mm MC brakes have been fully tested, both on track days and by carrying out multiple crash stops from around 70MPH on deserted roads and as result of those tests I consider that there is nothing inherently faulty with the ATE brakes, but there was an issue with the ratio between slave and master cylinders. Exactly the same fault can be found on early Norton disc brakes and the cure is the same, fit a 13mm M/C......
    #51
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  12. garandman

    garandman Wandering Minstrel

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    MC was sleeved from stock to 1/2” = 12.7mm.

    There’s a new piston and seals in addition to the sleeve. Also new pads and caliper adjusted.


    How much lever travel do you have?

    Going to adjust the linkage and handle at adjuster as my engagement is late and it comes too close to the bar. Snowed yesterday and 30’s today so no riding/tweaking yet.
    #52
  13. chasbmw

    chasbmw Long timer

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    I have the right amount of lever travel, much more than on the big OEM MC, but not so much that the lever is in danger of hitting the bar, even after crash stop testing. The wooden feel of the OEM brakes makes it more likely that you might lock the front wheel.
    #53
  14. garandman

    garandman Wandering Minstrel

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    Still need a little adjustment (and possibly more bleeding), but took a 35 mile ride yesterday and very happy with the result! The lever effort is "Normal" (ie like my other bikes). The lever travels more than stock but is not near the bars during a hard stop. A few miles into the ride I stopped worrying about having to gorilla grip the brake lever anymore.
    #54
  15. djd1230

    djd1230 n00b

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    I know this is an old thread, but I'm a new guy so what the heck.....
    Thinking of reducing the bore diameter on an R75/6 with the single ATE caliper as described above.

    Can you please tell us what seals were used in the master cylinder modification? It's relatively straight forward to have the under tank master cyl sleeved to 1/2" diameter and to turn down the piston to suit, but what to use as seals? My current cylinder bore is 0.565" diameter. (Probably a slightly oversized 9/16". This is about 14.3 mm.) Will the standard, under tank "14 mm" cup seals work with a 1/2" diameter bore?
    #55
  16. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Welcome to the forum djd.

    You know, in the old days - 50s, 60s and maybe even into the 70s you could get brake seals. I don't know where you'd get them these days. I have heard of using the seals from a Honda for something or other - don't remember what. The BMW seals and rebuild kits are a bit over-the-top expensive, especially when only a seal or two are needed.

    I think most of us have either sourced the smaller master, or just purchased an ATE rebuild kit. I think you're in virgin territory. Not sure you'll get any answers to your question so stay in touch and let us know what you find out and how it all works out. I'd like to know where to buy just the seals...
    #56
  17. OldCrustyStuff

    OldCrustyStuff Adventurer

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    Apple hydraulics has just the seals as they require your piston and hardware to rebuild after they re-sleeve. No clue if they will sell you just the seals or not but I’d start there.
    #57
  18. djd1230

    djd1230 n00b

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    Apple quoted $375 plus shipping to re-sleeve to 1/2", rework the piston and new seals. Add in a new hose, pads and a caliper rebuild and that's a $600 brake job for a single piston caliper. Hard to justify.
    Others can sleeve for less, but then I need seals.
    #58
  19. bmwrench

    bmwrench Long timer Supporter

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    Put a 12 or 13mm handlebar master cylinder on it. You'll never look back-except to make sure you're not about to be rear-ended.
    #59
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  20. djd1230

    djd1230 n00b

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    Certainly an option and probably less costly, but I'd like to keep the under tank master if possible.
    #60