Over in the "Road" section, but it occurs to me that the first time I came across one of these puppys was on a Motobecane Mountainbecane mountain bike (remember those?), so maybe it is of interest in this section...
http://www.retrobike.co.uk/forum/viewtopic.php?t=229247
http://www.retrobike.co.uk/forum/viewtopic.php?t=229247
