Subject: Re: Rear Derailleur Mounting Posted by: joey on November 16, 2005 at 16:37:36: In Reply to: Rear Derailleur Mounting posted by Scott Baxter on November 14, 2005 at 21:32:29:

Message: >I'm working on a '66 Raleigh Carlton frameset and want to mount a Suntour VX GT rear der. The dropout has an integral hanger, but the rear der stop bolt is way too short apparently allowing the der to rotate counterclockwise too far, resulting in a lot of chain slack. What are the specs if any for rear der rotational orientation, or how can one determine such a setting? I'm going to try to use a much longer stop bolt and see if I can get it to fix the derailleur against the stop on the hanger, but don't know how long is long enough. I think it is not that clear what you are asking. When you say the "rear der stop bolt" what is it you are referring to? The "B tension" screw is the rather small diameter bolt that screws in on the backside of the derailleur and rests against the derailleur hanger. Is this what you are referring to? If so, its function is to determine the position of the derailleur's guide pulley, and to ensure it doesn't contact the largest cog. If you are getting chain slack, and the derailleur is in otherwise good condition (no sluggish springs, for instance), chances are your drivetrain set up (cogs plus chainrings) is somehow exceeding the rear derailleur's limit. Or, you are using too long of a chain. Before proceeding further, I must admit I am not overly experienced in working on bikes as old as this. That being said... To check for too long of a chain, set the drive train up so that the chain is wrapped around the smallest freewheel cog and around the smallest chainring. If there is slack in this gear (and you have determined the derailleur is otherwise functional, good springs and all...), then your chain is likely too long and you should remove links. It should be just long enough the clear the rear derailleur's pulleys without slack. If you do remove links, you should then check to see that the chain can accommodate the other extreme (and be careful when shifting there...)--the largest freewheel cog and largest chainring. If it cannot accommodate that, that doubly ensures you have exceeded the rear derailleur's limit, and you need to find a new derailleur having a longer cage. In my experience, chain slack is either due to exceeding a derailleur's capacity, or a dead/broken rear derailleur.