ridethecliche

Background:
I worked my ass off to get together the money for a build I just finished. It's an 84 trek 760 and it has a mixed drivetrain. The front der is the original suntour superbe, the rd is a veloce, the shifters and cranks are campy centaur (compact crank), and the chain and cassette are shimano 105. I know it's a real crazy mix of components, but I put it all together about 2 weeks ago and it all worked really well. The LBS was amazed that the shimano spacing could be made to work and I was just thrilled that it all worked well enough to ride.

I raced the bike this past weekend and it didn't mis shift and let me down at all. It was a blast to ride and I was glad to be able to leave my cannondale at home since the weather was going to be nasty and I didn't want to end up crashing the bike (it was my first race).

I went out for a 25 mile ride on the bike yesterday and everything was working fine.

The Problem:
The problems started today, I set the bike up on the trainer and was spinning pretty easily. I was in the middle of the cassette and I decided to shift down to the smaller chainring. All of a sudden, there's no tension in the chain anymore. The chain is just gliding on top of the small chainring and it refuses to go onto the small chainring. If I shift up and down a few times from the big ring to the small ring, it'll eventually fall into place, but it was NEVER like this before. It just 'glides' or 'skates' over the small chainring and refuses to drop onto the small chainring...

While trying to do this, the chain not only dropped onto the bb off the small chainring, it also fell off the big ring and scratched the crap outta the finish of my cranks... I understand that I can drop my chain if I'm really badly crosschained and I shift in the front, but I have no idea how to fix this problem.

I'm really distraught about this and I honestly can't figure out what's going on.

Please help me out?

Thanks in advance.

Sirrobinofcoxly

Sounds like a question for the Mechanics forum

ridethecliche

Posted it there as well. I figure people here do builds all the time and might have some idea as to what is going on.

Thanks!

ridethecliche

It looks like the chain gets stuck between chainrings if I shift when on the middle cogs of the cassette, I guess this might make sense because of the angle of the chain, but the chain is a 10 speed 105 chain and the cranks are 10 speed also, as campy has been 10 speed forever...

Is a 10 speed campy chain much wider than a shimano one?

For now I guess I'm just going to have to mind my shifting habits and shift in the back before shifting in the front to avoid this happening.

Would it be possible to use a triple FD and lock out the limit screws so I don't throw the chain onto the frame? If I need a new fd, that might be the cheapest way to go about finding a working solution. An older shimano or campy clamp on FD?

Any ideas?

ridethecliche

Here's a picture of what it looks like.

grahny

How old is the chain & chainrings? First thing I'd do is put a new chain on and go from there.

RazorWind

Are the chainrings keyed somehow so they can only go on the crank one way? Maybe try rotating one of them with respect to the other so the teeth don't line up quite the same way.

Is there a way to increase the derailleur tension a little?

azdroptop

Bottom bracket and cranks are tight? Real wheel is centered between the seatstays? Cassette cogs are tight?

ridethecliche

Yupp to all the above.

GernBlanston

Same thing happened to me a lot of years ago. Like you, I was running a shimano chain and campy cranks. Turns out there's a spacing problem between the chainrings. The campy cranks are ever-so-slightly too far apart, and so the chain hangs up without engaging.

I gave up and upgraded to shimano cranks. You could do that, or figure out the spacing diff and machine some metal out of the cranks you have, or try switching to a campy chain and see if it works with your cassette.

GB

ridethecliche

The veloce ultra narrow chain is thinner than a shimano chain, so I'm not sure that's it.

Psimet2001 

The crank should work fine. The chain should work fine. FWIW Originally Campy ran a wider chain with 10spd, but it doesn't matter.

Honestly I think it's your FD setup or adjustment or compatibility. It just isn't kicking the chain over far enough quickly enough. Try playing with adjustment and cable tension to see if you can get it to shoot off of there.

Also not a bad idea to check for proper chain tension using the tension adjustment screw on the RD. Is your chain the right length?

I haven't run into this so it's hard for me to say without actually looking at it and running it. I've run into a ton of stuff too - although I have never run into anyone using a Suntour FD on a Campy 10 drivetrain either which is making me suspect the FD action with that indexed ergo lever.

Is the lever QS?

Also decreased cable tension would account for why it worked before, but now doesn't. Your housings have most likely settled since you built it....

All things to try

ridethecliche

Man. Thanks a lot for the insight. I guess I overlooked the amount I should have tightened the FD cable by. I tightened it a little bit and then stopped, and it still didn't work. Maybe I jumped to a conclusion on that.

I have since taken off the cranks and set them back to performance for an exchance and I've ordered a campy 2008 combined compact/regular double FD from pbk. That should help fix things. In the meantime, I think I'm going to go to the LBS and have them chase the thread on the RD and make sure that the RD is aligned. Next up, I think I might buy a shiftmate if needed, because I'd rather use shimano wheels than campy ones.

Thanks for your suggestions. I'll definitely give them a try when I get the parts back in and try them out again when I put stuff back on. I guess I was a little quick to jump the gun when I started looking for problems other than just the tension...