Zinn-X

This is really weird. I'm using a Shimano 105 crankset and FD. It has no problems switching from the big to the small ring, but it has issues going from the small to the big ring.

I will dial in a perfect tension with the upper limit screw and it will work fine for about fifty miles or so, and then I'll start getting either overthrow or grinding/no shifting. It happened on a group ride yesterday and everyone was kind enough to stop while I pulled out my screwdriver (I bring it everywhere now) and made a quick adjustment. But it's getting kind of old.

The bike doesn't have that much distance on it. Maybe 3000 miles. The drivetrain is in good condition with a new chain, and newish cables. So... wtf could be causing this?

JiveTurkey

If it is just the screw loosening itself, try some blue Loctite.

tellyho

Sounds like you might still be breaking in the cables and housing to me, AKA cable stretch. This could definitely cause your symptoms (derailleur travel not sufficient), even if dialed in beforehand. If this is the case, it should settle down after a couple rides. As I recall, mine lasted maybe 200 miles the last time I replaced cables.

Zinn-X

Well, it's definitely been several hundred miles since I replaced the cables, so the possibility of cable stretch seems kind of remote. But it really does seem quite similar to what I experience when breaking cables in.

I think I'll go with the blue Loctite idea. That stuff seems to work miracles

Little Darwin

Just brainstorming, so don't be insulted if I ask obvious questions.

What was the last thing you changed before this started happening?

Did you replace cable housing? If so, did you use SIS shifter cable housing?

It sounds likke sometimes you need to adjust it in, and other times adjust it out... Especially with this fact it makes me think that something is moving, either in the cable or the derailleur itself. Can you fairly easily twist the derailleur around the seat tube? Is there any wobble in the derailleur?

Another possibility is to examine where the housing enters the cable stops... Is everything fitted properly? When you shift all the way, is there too much slack in the system? Enoiugh to cause the housing to move out of the stops?

If your cable goes under the BB, is it in the slot that it is designed to go through, or sitting beside the slot?

Unless the screw is real loose (almost loose enough to adjust by hand), I don't really think locktite is the solution, although it won't hurt.

In summary, check the entire cable path from the shifter to the derailleur with the front in the high and low positions and see if everything is as it should be, without excessive slack in the cable.

Retro Grouch 

Check where your cable housing butts against a cable stop on your frame. I'm betting you'll see a few individual little wires. That's a sign that your cable housing is gradually shortening itself. When that happens, you can adjust the derailleur perfectly only to find a short time later that it needs the exact same adjustment again - just like you reported.

Replace your cable housing. Make sure the housing is cut square and the housing ends are firmly seated and you'll be good-to-go.