Ok, I have an '84 Schwinn Traveler 12 speed with Suntour ARX friction shifters. As far as I know the components are original. It was a gift so I can't be sure. My chain only slips on the 3rd largest sized cog/gear in the back. Here are some pics:
http://s755.photobucket.com/albums/x...t=PIC-0052.jpg
http://s755.photobucket.com/albums/x...t=PIC-0054.jpg
When I am pedaling it's like the chain wants to jump to a smaller sized cog/gear but never actually makes it and I can never trim up my gears on this cog but I can on all the others. This happens any time I am in this gear and never in any of the other gears. I thought that maybe I had a stiff link but when I checked there was no stiff link. I also checked to see if my chain has stretched and just needed to be replaced but it is also fine. I also checked to see if my front cogs were worn and they are not.
I just had the crank adjusted. It was making a tick tick clunk sound but now it is fine. It just needed some tightening. I don't know if this has anything to do with the chain/gear problem but thought it might be some helpful info.
Any info or advice would be greatly appreciated. I tried to be as detailed as possible. If more info is needed let me know. Thanks so much.