derailleur problem

[ginny]

At least I think it is... I hope you can help me, girls. I have a tripple chain ring in front. I ride a 50cm Bianchi Eros Donna - I hear it has a really short wheel base and I don't know if that contributes to my problem. Here's the problem. Apparently, on some tripple chain rings, if you are on the middle chain ring in front, and the smallest in back, it sort of acts like it's cross chained. I was doing a really big hill ride a couple of months ago and when I was in the middle chain ring and the smallest on in back, my front derailleur decided to shift me in to the smallest chaing ring in the front. It was such a hard hill that I proceeded to FALL OFF MY BIKE! I was all irritated, and got back on, shifted to a slightly harder gear behind and left it in the smallest chain ring in front. Then, as the hill got even steeper, the stupid chain randomly shifted all the way off the front chain rings! I FELL OFF MY BIKE AGAIN!!! I was SO mad! So, I took the bike the my friend who is a bike mechanic and he told me about the effective cross chain thing. I haven't had the bike in the middle chain ring in front and the smallest behind since then. Last night, I went for a hard hill ride thinking this problem was solved with some tinkering by my friend, and it happened again! I wasn't 'cross chained', and I didn't fall off, but I did have to stop on a big hill! So, I left it in the smallest chain ring in front and shifted to a slightly harder gear behind and kept riding. Now my chain would sort of 'clink' occasionally - like if it was hitting something - but it wasn't. Can anyone diagnose this? I have had the chain measured and it isn't too stretched out (was about 25% stretched at the beginning of summer). Maybe I should have it remeasured? Is this a major front derailleur problem? Is this a 'cog' problem? Do you think I will need a new front casette? Or rear casette? Sorry for the long post!

[alpinerabbit]

Sounds like the drivetrain needs a tune-up? or could the deraille(u)r be bent? LBS can check for chain or cog wear at the same time.

[OakLeaf]

With a steel frame, sometimes frame flex can cause a bike to shift on its own. Were you standing to climb?

[DebW]

It's more often flex in the crankset. Check the crankset for trueness, also. And make sure the bottom bracket is correctly adjusted and the arms are on tight.

[aicabsolut]

it could be frame flex under load
it could be your chain is getting too worn

It might also be that you need a new derailleur cable because it is losing tension.

Check to see if you can just tune up the indexing without replacing the cable:
(instructions for a triple
1. Shift chain to middle chainring in the front and innermost (largest) rear sprocket.
2. View gap between inner cage plate and chain. Gap should be as small as possible without rubbing chain.
3. To reduce gap, increase inner wire tension by turning barrel adjuster counter-clockwise. Adjusting barrel may be on frame or on shift lever. Check gap again.
4. If chain is rubbing cage, turn barrel adjuster clockwise, or inward toward shifter body.
5. If barrel adjuster is all the way in or out and no adjustment is possible, reset inner wire tension. Shift to innermost chainring and loosen inner wire pinch bolt. Pull wire gently with fourth-hand tool and tighten pinch bolt. Begin adjustment of inner wire tension as above.

I'd expect that you'd find you need to tighten the cable. If tightening the cable causes problems with rubbing, you might need a new cable and/or chain (i.e., either the cable is just failing on you when set properly or the cable isn't your problem at all). If tightening the cable causes no problems, then check the indexing by making sure that you can still shift into the other rings, particularly the little ring. It is too tight if you cannot shift into the little ring on purpose. It is too loose if you have slow shifts into the large ring.


it could also very well be your cross-chaining.

When you're in a fairly hard gear under heavy load, there will be a lot of tension on the top of the chain, and the chain will be kind of slack on the bottom. this can cause the chain to jump in all kinds of ways, especially on a flexible frame. The most extreme is that in a sprint effort, the chain can jump into your spokes. More commonly, it will drop rings. You can avoid it a little bit by picking a gear where the chain is straighter or by trying to spin more in an easier gear.

If you work on the cables (including replacing them) and follow your friend's advice and it is still a problem, then most likely, you're due for a new chain. When you check the chain, you should also check the cassette for wear.

That clink you heard was probably the chain rubbing on the derailleur from being in the little ring and a small cog.

[sundial]

Can someone post pictures of how to adjust the derailleur on a compact double? I'm a visual aids kind of girl. My LBS adjusted it on the stand but when I took it for a ride today, it's not quite right. It works fine in the large gear but when I shift to the 34 and the chain is in the middle of the cassette, it feels like it's slipping on the cassette, like it's not hitting the teeth right. The bike shop isn't exactly convenient to me. My bike is a '08 Specialized Roubaix.

[mayanorange]

http://www.youtube.com/watch?v=ngm6dr-1na0

They also have how to do the rear and a bunch of other handy videos. I figured it out watching these a few times, trying it, getting stuck, watch again, then it was easy once I got the concept.

[aicabsolut]

Can someone post pictures of how to adjust the derailleur on a compact double? I'm a visual aids kind of girl. My LBS adjusted it on the stand but when I took it for a ride today, it's not quite right. It works fine in the large gear but when I shift to the 34 and the chain is in the middle of the cassette, it feels like it's slipping on the cassette, like it's not hitting the teeth right. The bike shop isn't exactly convenient to me. My bike is a '08 Specialized Roubaix.

Sounds like it's a rear derailleur issue. It's common for it to seem ok on the stand but to start acting up under load. You probably just need a little turn of the barrel adjuster. Are there any delays in shifting one way or the other (does it keep skipping instead of shifting)? If that doesn't work, check that the B screw is set right and that the derailleur hangar isn't bent.

http://www.parktool.com/repair/readhowto.asp?id=64

(has pictures)