I have a late 90s early 00s Cannondale R800 with full 105 components. I tore the bike down and rebuilt it in 06 with new cables, paint, brake pads and rebuilt and repacked the bottom bracket. I also installed a quill stem adapter so I could put a clamp on stem on it to get the angle and length I wanted.
After everything was all set and running perfect my idiot brother dropped it, a whopping 2 rides into the new set up. When it fell over it landed on the derailleur side and bent the hanger, which after attempts to get it straight by a local shop it ended up snapping mid way up a hill, not fun. I replaced the now cracked hanger with a new one, and readjusted the cable and shifting.
A few rides in I noticed that the chain would jump down 2-3 cogs when I would freewheel (back pedal) and when I pedaled forward it would return to the normal cog. Now this only occurs when in the highest 2 cogs but it is still quite annoying. I have adjusted the cable at both ends to no avail and after 2 years of dealing with this I want to get it fixed.
I'd like to do it myself so any tips as to the cause and how to fix it would be greatly appreciated. I have a feeling the rear derailleur is slightly tweeked but not sure how to align it or check it for that matter.
Without a proper hanger alignment tool, it could be hard to do well, though I do it frequently. (Oops, that sounds like boasting.) Anyway, you have to align the hanger so the pulleys are in the same plane as the sprockets.
My procedure for alignment without the proper tool:
Leave the derailleur in the hanger. If you take it out, you will deform the threaded hole.
Eyeball the alignment.
Stick an allen key into the mounting bolt. Bend the hanger with the allen key.
Remember that there are two planes to adjust: the one with the axis visible from behind the bike and the one with the axis visible from above the bike. I think the one that's out of adjustment for you is the latter one. In other words, the front of the pulleys is to the left and the rear of the pulleys is to the right. Or vice versa.
Gee, I wish I could make a video.
This is the proper tool. It's a bit too expensive for a home mechanic who won't have to use it more than once a year.
Ok, thank you for the serious replies. I would assume that if the hanger were out of alignment that once I replaced the broken one with the new one I should have had it aligned at that time. I'll take a look at it and see what I can do.