The design does not involve an upper pivot spring, so that's why you're not finding one. It's sup
The ones I have come with a captive Allen-head bolt and a washer on the frame side. The washer has a tab that is bent toward the bike. There are two designs of this washer: one for French frames, and one for all other frames. The one for "all other" fits Campy and Shimano steel dropouts perfectly. With this matched up right the parallelogram sits at an angle about 30 degrees ahead of vertical. The cage angle is then a result of the gear selected and of chain length. I can always pull it backwards to allow the wheel to release from the frame.
Your Motobecane could have the French derailleur tab design or the Campy one - Moto seemed less devoted to French sizings than some other French makers. But the tire deflation issue: I think that's just that the chainstays are considerably shorter than on some of your other frames, and perhaps your tires are too big for the frame? I'm using Duopars right now on a 1984 Trek 610 with 43 cm chainstays and a 1980 Woodrup with 44 cm. Both are a little shorter than your Trek 720, and I would just be guessing on your Schwinn's dimensions, but few frames have longer chainstays than a Trek 720. On my two bikes I have no issue with wheel extraction while the tire is inflated.
It could also be that Moto made long chainstays, but mounted the chainstay bridge too far from the bottom bracket, artificially constraining the wheel extraction clearance.
On Mon, Jun 7, 2010 at 12:02 PM, Calvert Guthrie
<calvertguthrie@gmail.com>wrote:
> What's with the main parallelogram frame attachment bolt?
> There's no coil spring & it doesn't swing back
> to allow the spindle in and out of the dropouts.
>
> I got around it on my long Trek 720 and my Schwinn Voyageur ('84 touring)
>
> I shifts perfectly on my somewhat shorter-stayed, triple, Motobecane Grand
> Touring
> but the tire needs to be airless to get the wheel on and off.
> I'm working toward a finesse but at this point it is still a fight.
>
> Fancier spindle nuts with bails, &c. make it particularly awkward.
>
> Is there a retro-fit option that'll get me beyond this burr?
>
> Or should I just get used to it?
>
> --
> Calvert "Where's My Hammer!" Guthrie
> Rector Director
> KC Center for the Ink & Paper Arts
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>
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>
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>
> calvertguthrie@gmail.com
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--
Ken Freeman
Ann Arbor, MI USA