My brother bought a Trek 2120, 1997 or 1998, that had been upgraded to a mix of 105, Ultegra, and Dura-Ace. Last week his chain skipped of the rear cogs and caused a crash. Upon further investigation we might have some capatability issues. Here are the components that are on the bike. I know an obvious problem right away is the 8 spd in the back and the 10 spd chain. Are there any others?

Crank: Dura Ace 7700
Chain: 10s
Cassette: 8 spd Hyperglide
FD: Ultegra 6600
RD: Ultegra 6500
Brifters: 8 spd 105SC STI

how is your brother? did the chain come off either end of the cassette or simply slide over them? I would check the chain/cassette for wear. it is possible that the chain is just a bit too narrow for the cassette

I would second bianchigirll: chain too narrow

Thanks for the concern. Thankfully he was ok. Just game away with some scratches a bruises, nothing broken or fractured. The chain came off the top of the biggest cog. Luckily there was not damage to the spokes because there isn't a guard. I'll have him look at the level of wear and the fitting.

O, if it came off the top cog, then it is probably just an issue of aligning the RD. Make sure that the RD does not go past the largest cog, a screwdriver and a quick test should fix that right up.

Glad he's allright!

+1 Sounds like the limits were not properly set.

yes I agree with the limit or the even a bent hanger. OH get him a real big dorkdisc for christmas *giggle*

Thanks for the responses guys. I had at first asked him about the alignment and he said it was good. I'll have him take a look at that again.

I plan on it. Where he uses it or not is the question

The only item in the list that wouldn't work is the chain. A 9-sp chain is a lot cheaper, and an 8-sp is too wide for your FD, it will rub. I agree with everyone on the adjustment issue. I've run 8-sp components with 9-sp cranksets a lot, both with Campy and Shimano. I simply wouldn't buy a 10-sp chain unless I had to.

Here is the thing:

I am huge believer of getting components of the same gruppo and installing them together just to avoid such a thing. And I am glad that your brother is ok. If I were him, I'd sell the Dura Ace crankset, the 6600 FD, the 105 brifters and replace them all with 6500 components (he might actually come ahead in the equation.) Also, I'd double check on that cassette to make sure that it plays nice with the RD.

Mixing and matching is ok for simple components, like hubs or headsets or seat posts or pedals etc, but the drivetrain has to match as close as possible. In the "good" ol' days of friction shifting, things were simpler, but when you get into indexing, mismatching components is a dangerous dice roll...

The other possible factor is pilot error -- one should never downshift into first gear at a moderate to high speed. I mix and mismatch components quite freely, and I never have problems with overshift. I can, however, make the "wrong" chain skate over a somewhat worn freewheel with a 1- or 2-tooth progression.