Rear derailleur skipping

[Fritz]

I bought a 2 yo caad 9.5 from a friend, maybe 400 miles on it. Ran excellent, like a dream, the first few rides. The other day the rear derailleur couldn't seem to find a middle gear and be happy, it skips around when not on the highest or lowest sprocket.
No stiff link observed.
I gave the barrel adjust a little tweak. That has brought the chain too close to the front derailleur cage.
Nothing appears to be bent. It hasn't taken a thwack.
Do I continue myself (I always though I was reasonably mechanically inclined, heh, heh, heh) or bring to the LBS?

[Joe_W]

Hm. I'd follow the adjustment procedure described here http://bikeride.com/part/derailleur/ . I do not understand the part in your post when you adjust the cable tension of the rear derailleur and you run into problems with the front derailleur... I also experienced slight skipping / mis-shifting the first months, a quick turn on the barrel adjuster usually fixed that. It took the cables some time to settle to their final length...<br />
Check cable housing for kinks or suspicious looking bends, they can be the source of some weird behaviour.
If that does not fix your problem, you might want to check for chain wear, though it should not occur after only 400 miles (unless riding in ugly conditions and pushing very hard) or for proper alignment of the RD, maybe something is bent.

[Fritz]

thanks Joe. I eventually read beyond the video and realized the barrels needed a tweak. I managed to get back to a happy medium and all is pretty good now.
There is a very slight rub of the FD cage and the barrel of the FD is at one of it's limits.<br />
If I "center" the barrel and take up tension on the cable itself at the cable bolt, would this in theory give me the "room" I need to adjust away the rub?

[Joe_W]

Do you have two or three chain rings in the front? Whcih gear combination is "off"? From your post I guess that in the high-high combination the FD is slightly too far inward. First try to adjust the high limit screw on the FD. If that does not help, you might benefit from a higher cable tension, though the cable tension is (usually) not used to adjust the limits, but only the position of the middle chain ring (and of the trimming steps). If you have a Shimano group, you should take a look at http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50lparsys-0030-downloadFile.html/06)%20Trim%20Function.pdf (save this file, I do not know how long it will remain online, it is no longer linked from the original page...)
I first did not know where the trim steps should go and completely mis-adjusted the FD...

[Fritz]

2x10.<br />
Yes, high-high is rubbing a bit.<br />
So what does the trim barrel do for a 2 ring FD?
That's why I was wondering if I should pull up a bit on the cable bolt of the frame after moving the trim barrel of the FD to a mid point.

[Joe_W]

Well, if you cannot fix it with the high limit screw, then adjust the cable tension and play a bit with the limit screws and the cable tension. Even for a 2x10 trimmimng can be neccessary if you want to use certain combinations, the FD cage needs to be shifted a bit from the position, where high-high does work to a position where high - middle gears is running well. The limits of a derailleur are adjusted by the limit screws, the cable tension sort of adjusts the positions in the middle (ok, it adjusts one position, the way travelled by the derailleur is chosen by the amount of cable being pulled by the shifter). Some new groups seem to have gotten rid of trimming...
Warning: misadjusting the upper limit may cause the chain to drop from the chain ring, resulting in a crash, bring the FD outer cage plate as close to the chain as possible in high-high combination!

[Fritz]

K, Joe. thanks. I'll give it a go.

[marcdominic]

I always have difficulty in re-indexing the rear dérailleur: usually because of my forgetfulness after re-fitting the rear wheel to switch to the middle chainring on the front chainset. So, I end up setting it up on the lowest chainset ring - and of course this doesn't work: I need to set on the middle chainset ring, doh!
I've just replaced the rear wheel (after a split rim on some old Mavics) and of course had to re-index the rear. Would you believe the same thing happened again...?