Chain Not Sitting Right in "4" Only
 

I'm stumped.

For about a year, my vintage 1996 GT Outpost (the love of my life) has not been able to ride smoothly when I am on the fourth cassette ring. Occasionally, "5" and "6" are problematic, too, although not as bad.

The problem feels like the chain is not connecting with the ring quite right. It's not slipping and I don't really feel it rubbing against the adjacent ring. It just feels like the chain is missing the teeth by a minuscule amount, or like there's a piece of dirt stuck somewhere. Interestingly, I don't really hear it or feel it when the bike is on a workstand, but it comes back big time once it's back on the road. Here's what I have done so far:

1. Adjusted the derailleur barrel ad nauseum with hopes that it's just a tension problem
2. Replaced the chain
3. Replaced the cassette
4. Replaced the entire rear derailleur
5. Changed the pedals, thinking maybe I was wrong about where the problem was coming from
5. Tightened the cassette because I noticed it was a little loose today

I have also had the bike looked at by three different mechanics who can't seem to pinpoint the problem. All have told me not to worry, and to just keep riding it into the ground. (That's the problem when you insist on keeping an old bike on the road. Everybody treats it like your old grandfather who is dying of congestive heart failure. "Just keep 'im comfortable and make sure he enjoys the rest of his life.")

This bike has traveled thousands of miles with me and just got off two overnight rides to points out-of-state. I don't plan on hanging it up anytime soon. However, I am starting to not enjoy riding it as much because of this persistent problem.

One crazy idea I have is to replace the front triple chainring with a single so that the chainline has a better chance of running perfectly straight. Right now, the bike is a 3 X 7 and I almost never use anything but the middle ring.

Can anybody think of anything else**********

I do not see that you have checked your rear derailleur hanger alignment. This is my first step in diagnosing any rear shifting issue. I also do not see that you have attended to your cables; perhaps there is a kinked wire or housing somewhere, or a frayed wire.

The best of the three bike mechanics checked and tried to adjust the rear derailleur alignment and ended up replacing the entire derailleur. I forgot to mention that, before going that route, I replaced both pulley wheels on the old derailleur.

My cables were both changed when I replaced the rear derailleur. And anyway, wouldn't bad cables affect ALL the gears and not just one or two?

Operator error (cross chaining)?

cassettes should never be loose - they need proper torque and that proper preload is going to change the spacing on a small scale
on this Miche cassette, 45N-m is a honking big torque - check mfg spec for your cassette
http://img.photobucket.com/albums/v7...aaP7030002.jpg

Sounds like you have covered most of the bases ie. chain, cassette and derailleur. Was the new chain sized correctly? From your description of the problem it is difficult to diagnose, is it actually making a noise when riding in that cog or is it just a rumbling through the pedals that you are feeling/hearing? With regard to going to a single up front your current middle chainring should be your ideal chainlne so a single should make no difference. Things to consider...how worn are the chainrings, if the noise/rumble? feels like its coming from the rear is it time to overhaul the hub +freehub? then there is the front end..bb + chainline to consider since it only happens under load flex at the bb end and loading on the hub/freehub may provide an answer..good luck

I assume it was. But anyway, I was having the problem with the old chain, too.

It's more of a rumbling through the pedals, which is why I suspected bad bearings in the pedals early on.


Yeah, I kind of figured that. But I can dream, can't I?

The chainrings on the front end (I assume that's what you mean) are not really showing visible signs of wear. I changed the crankset a few years ago, too. And although the rear wheel is within two years old, I do notice that it's a little crunchy when spinning, as if the hub bearings have been eating sand. However, again, the problem only occurs in one or two gears, so I can't really imagine the hub causing this problem. The bottom bracket is a few years old now, but is not ticking or showing signs of wear.

Thanks for all these suggestions. It sounds like I am not the only one who is stumped by this.