Front just won't shift consistently
I'm in a bit of a situation that seems to be above my current mechanical aptitude, so I come to the altar of bikeforums to seek guidance. My gf has a ~2 year old Jamis Quest (1500 mi or so on it), all components still stock with front shifting that just won't stop sucking. According to her it's never been great but degraded just before she stopped riding in the winter. I consider myself passably acquainted with derailleur setup... I've built up bikes from scratch and maintain 4 in my stable and they all work great.
- 105 for STIs and Double band clamp FD
- TruVativ Elita Compact 50/36
- Difficulty shifting from little -> big. About half - 2/3 of the time it'll grind for 2-5 revolutions and finally pick up (with my hand holding in the lever the whole time). The other times the derailleur will move but the chain will just never pick up onto the big.
- Tendency to drop chain on shifts in either direction.
- Occasionally the lever will get "stuck" in the big position--it takes a tremendous amount of force (several times normal) on the small paddle to get it to let out cable again.
I started out with adjusting the limit stop screws, and it seemed to shift fine in the stand. Back out on the road, however, and it goes to crap again. The cable was all frayed (apparently they were never capped by the shop) so I replaced that and re-adjusted limit screws and cable tension until it was fine on the stand. On the road test, it shifted great about a dozen times, and then back its old tricks. Taking a closer look, it seemed that the derailleur was mounted a couple mm too high, so I lowered, checked alignment and tried again. It seems that no matter what I try, I can't get the derailleur in a position where it'll consistently shift. The cables (but not housing) are new... it looks to my eye to be mounted straight and is within the spec'd 1-3mm of the top teeth... the levers look to be in good condition (and have definitely never been wrecked)... so any ideas what the heck is going wrong?
Since I've fiddled with the derailleur to no avail, my suspicion is now on the lever. I think I might slap on a friction downtube shifter and see if that works fine. I've got some Shimano Exage (early 90s, I think) downtubes I could test out--would that test work, or has the pull ratio changed in the intervening years?
Any other advice to try out?