Frankenbike problems
 

Hey all,

I recently built a frankenbike from lots of pieces from lots of bikes about to be abandoned, or already abandoned. So far it's working fine except when I ride over a bump, it shifts down one on the rear cog. I was thinking that it might have something to do with the derailleur cable tension, but honestly I have no idea. This is the first bike I've ever built. Any suggestions?

Thank you!

Tell us more about the bike. Type of shifters? Derailleurs? ect. Close up pictures of the shifters, cable arrangements, and drivetrain would be helpful.

http://bikeforums.net/attachment.php...hmentid=247841http://bikeforums.net/attachment.php...hmentid=247842http://bikeforums.net/attachment.php...hmentid=247843
Cables are all new. The rear derailleur, I believe, was the one initially attached to the bike.

Since you replaced the cable,(and checked it for sticking?), I'd guess the derailer is sticking, possibly from a loose or worn fastener on it.
Take it off, inspect, clean, and lube it. You might want to just hose it with WD40 or similar, and see if that helps.

Adjust the tension on the shift levers. If it is insufficient they will move when you hit a bump. Tighten the hold down bolts.

Thank you. I'll try those, ride today, and hopefully the problem will be solved:)

+1. Friction shifters have to have enough "friction" to hold the cable in its position, despite the fact that the derailleur's spring wants to move it.

+2 one of my favorite blank stare, mouth agape "fixes" at the coop for a bike that doesn't hold low gears. No tools needed.

OP: we're all talking about tightening this guy, circled in this pic-

http://i.imgur.com/psVv6l.jpg

Anyone who ever used Campy's old Record downtube shifters soon learned to keep the D-rings tight. These things were notorious for spontaneous loosening and allowing "ghost shifting", always at the worst possible time.

Thank you all so much! I tightened those little guys and had a much better time riding today, even got muddy:)