pre-'91 Cannondale Derailleur Hanger Replacement?

Discussion in 'Cycling Equipment' started by lazystar, Nov 16, 2006.

  1. lazystar

    lazystar New Member

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    I just bought a (seemingly) pre-'91 Cannondale R700 road bike with 26" wheels that the owner was selling "just for the parts" (mostly 105 group). He was sure the frame was a write off because the derailleur hanger was broken, and he didn't want to deal with any hassle, so it came pretty cheap.

    Of course derailleur hangers can be replaced, right? Problem is that pre '91 and post '91 cannondale hangers are ever so slightly different in terms of bolt spacing and bolt guage. I needed to borrow the mechanic's digital micrometer at the repair shop to show him that the hanger he said was the same as the one I had pulled from the bike were not identical, so convinced was he that they were. Why Cannondale made the slight modification to the specs is beyond me, and though they have a lovely 1 page technical drawing PDF of the two models on their website, I have been told that they only make the post-'91 hanger these days.

    So the question is: has anyone found a retail source for the pre-'91 hangers, or has anyone found a work-around that solved the problem for them (such as drilling and retrofitting a different hanger, or getting a copy of the Cannondale hanger machined custom-like)?

    Any help or suggestions that will help me preserve the otherwise good frame are much appreciated

    PS: drop-outs are not horizontal, so making a single gear of the frame is a hassle that I am avoiding exploring unless it really comes to that!

    Thanks.
     
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  2. alfeng

    alfeng Well-Known Member

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    FIRST, and don't take offense at this remark, but Anal Retentives should not buy vintage used bikes that need work ...

    Now, that we have that out of the way, presuming/hoping you don't fall into that category, let me ask:

    Is the NEWer derailleur hanger larger or smaller?​

    If it is larger, get a flat file, and shave it down to fit ... make a template if you can't do this work by eye.

    "... different bolt spacing and bolt gauge" -- what does that mean? How different? How slight?

    Do you mean the holes don't line up perfectly? One of the two holes can certainly be(come) a slot ... you can countersink/chamfer the slot to allow a bugle-headed bolt to fit flush if that is what you want.

    You can get some STOCK metal and fabricate your own hanger ... 10x1 is, I believe, the threading for the derailleur's mouting bolt.
     
  3. serenaslu

    serenaslu New Member

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    Your best bet may be to modify or fabricate one as Alfeng said.
    From looking at the diagram on the link you provided:
    http://www.cannondale.com/bikes/tech/kitlist/CA.1.1.2.Road%20der.hangers.pdf
    They appear to be essentially the same body; I'd give it a shot.
    It certainly looks like you should be able to clamp it in a drill press and drill out the holes from 3.08 to app. 3.67 mm, doing one of them just slightly off-center towards the other one. (.01mm is hardly even manageable).

    It's probably going to be tough to find one stock as there were only a few applicable years, as early Cannondale frames, such as the old '86 frame (gad, can't believe that I've had it twenty years now, sigh) that I still occasionally ride; have a frame integral non-replaceable hanger.
     
  4. lazystar

    lazystar New Member

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    I thought the bike was, maybe, at earliest, a '95; hardly vintage in my books. Maybe someone who knows Cannondales could date an aluminum R700 road bike with 26" wheels and 105 components; seems a strange mix to me.

    Definately some good ideas you bring up though...if I were a skilled machinist with a suitable shop. So, at the risk of setting off your finely attuned A.R. radar (how did you develop that?), let me supply the specs that you request (they are also in diagram form in the PDF linked to in the first post):

    There are two measurements that changed in 1991: the space between the mount bolts, measured centre - centre, and the diameter of the holes (and bolts) themselves. The details are as follows:
    pre '91: c-c spacing - 15.48mm; hole dia. - 3.67mm
    post '91: c-c spacing - 15.49mm; hole dia. - 3.05mm

    So basically the holes got very slightly farther apart and smaller, but when you do the math the smaller holes on the new hanger fit entirely within the diameter of the larger holes on the older hanger.

    The current thinking is that I buy the new hanger and get a very precise machinist to drill the holes larger and closer together for me.

    Does anyone know about that sort of thing? Can you drill a hole with a centre that is 0.005mm off the centre of an existing hole? Can you easily match the guage and thread-spacing of a 16 year old bolt? I know that conventional metal drill bits skitter into preexisting holes that are two close to (ie, overlapping with) where you want the new hole to be, especially if the bit is a narrow guage one to boot. But how is precision machining done now? With high-pressure water? Lasers? Force of will?

    I realize we are talking pretty fine difference of measures here, and though I suspect that might matter somewhat, correct me if I am wrong on that account. Maybe the forces on the derailleur hanger are not really all that great, and a little sloppiness in the hole size wont matter at all. Maybe a small round file and some lock-tite will do the trick?

    Any other ideas/knowledge?

    Thanks
     
  5. supergrill

    supergrill New Member

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    Umm...isn't that exactly what Serenaslu suggested in the preceding reply? Just use a regular drill press (someone you know is sure to have one). Just be sure to support the space between the plates with a piece of scrap wood or such to support it while you are drilling and use a new sharp bit. As was stated you'll never get that precision on the original piece. Even if you need to reem it out slightly one way to fit after the drilling it shouldn't cause any problem with slop on the hanger.

    Shouldn't be any problem. May have to hunt around a couple of hardware stores is all.
     
  6. lazystar

    lazystar New Member

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    You know, it took me a while in the fog of frustration to realize why the original post was considered potentially anal-retentive, until I read what you said about "0.1mm being hardly manageable". Suddenly it all clicked: we are really only talking about a difference of 0.01mm here which is equivalent to roughly nothing. Surely a steel bolt will re-channel an aluminum/soft steel hanger as it requires, right?

    Your point about supporting the upper side while drilling is also well recieved Serenaslu. The upper side is an oversized clearance hole, the frame is threaded to the bolt guage, and that means the only challenge is matching the threading on the wheel side of the hanger, or drilling it close enough that the bolt can carve a path for itself and maybe sealing the whole thing with locktite for good measure.

    Even if it goes horribly awry, I could just drill and tap the hanger and the frame to a heavier gauge and use other bolts.

    Thanks so much to everyone for putting their heads together to help me figure this out.

    Good to know: that only leaves 87-90 as the potential range for this earlier hanger, perhaps even fewer years. That is enough to end my search for an original hanger right there. It is good to hear that frame should have some more life in it though.

    Thanks again. M-
     
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