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  1. #1
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    are most rear derailer mounts the same?

    I'm curious, over the last 20 or 30 years or so, are the derailer mounts on bikes, whether they be road or mountain frames, the same? For example, could I put a newer shimano xt rear derailer on an old, early 80s road frame? The threads appear to be the same, are the derailer stops in the same position, or close enough?

    Thanks for any info.

  2. #2
    sch
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    The standard thread mount for frames is 10mmx1.0mm, this dates from the '70s as an essentially universal mount. IIRC the French used a weird thread with 26TPI, which is so close to 1mm pitch it could be used with 10x1 bolts with little interference. With the demise of the intrinsic Fr component industry,
    at least as far as der/shifters/brakes went, the shift to 10x1 was easy. You should have no problem mounting the der. Worst case of stripped or odd threads, you can drill out the threads and the Small Parts place sells a T nut that can be put in the hole that is internally threaded for 10x1 and allows der mounts in that situation.
    Steve
    Last edited by sch; 06-14-06 at 03:51 AM.

  3. #3
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    Ah, nice. I ask because I'm wondering if I found an older steel touring frame (like a miyata 1000 or something), if I could build it up with newer mountain/road components for a touring bike.

  4. #4
    Gone, but not forgotten Sheldon Brown's Avatar
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    Quote Originally Posted by sch
    The standard thread mount for frames is 10mmx1.0mm, this dates from the '70s as an essentially universal mount. IIRC the French used a weird thread with 26TPI, which is so close to 1mm pitch it could be used with 10x1 bolts with little interference. With the demise of the intrinsic Fr component industry,
    at least as far as der/shifters/brakes went, the shift to 10x1 was easy. You should have no problem mounting the der.
    Basically right, but Italian, not French.

    There used to be different standards for differnt brands of derailers. Huret, Simplex, Campagnolo, Benelux...

    The industry eventually standardized on the Campagnolo style, which was 10 mm x 26 tpi (Italian threads are weird that way...metric diameters with inch-based thread pitch) and has evolved into 10 mm x 1.0 mm pitch. 1.0 mm pitch is 25.4 threads per inch, close enough where the threading doesn't run that far.

    A similar evolution occurred with the down-tube braze-ons for shift levers, again with Campagnolo becoming the de-facto standard.

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  5. #5
    sch
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    I was misled by my ''69 or '70 PX10 which had the 26TPI and when the rather awful plastic Simplex was changed out to a Suntour I ran a 10x1 tap through it as the Japanese used that as a preferred thread.
    Steve

  6. #6
    Gone, but not forgotten Sheldon Brown's Avatar
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    Quote Originally Posted by sch
    I was misled by my ''69 or '70 PX10 which had the 26TPI and when the rather awful plastic Simplex was changed out to a Suntour I ran a 10x1 tap through it as the Japanese used that as a preferred thread.
    Steve
    Actually, the Simplex dropouts were not threaded at all, but it has long been a common upgrade to run a tap through them so some other derailer can be used. This usually also entails filing a notch for the "b tension" screw to bump up against.

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