As a keen mtb fettler and having installed and maintained approx 20 cassettes, 3 different derailleurs, built a bike from scratch etc with the associated indexing required, I think I've got a pretty good handle on this sort of mechanics.
I took the plunge into road biking this year an got a Defy with 105 shifters. These have worked perfectly for 6 months but now can only be described as 'sloppy'.
So working through the options I:
Installed new 105 cassette and chain.
Straightened hanger, then bought a new one anyway.
Cleaned and lubed all the cables, including unwrapping the bar tape and lubing the shifter mech.
Yet still the shifting is imprecise.
Basically I can get it to move accurately down from the big cog to the smallest responding well to each click, but then it takes a double click to start the return and when riding I've lost the reliability of click-shift. Now have to 'feel' it in with the large lever.
It's all very frustrating. I bought 105 because I thought it was comparable to xt quality, have I been mistaken? Is this a case of flogging a dead horse and an upgrade is the best solution. Is it the shifter or the derailleur that is most liable to be a bit naff?
Is the rear mech bent? Your comment about changing the hanger suggests there might be some previous in this area!
What cable are you using? IMO Shimano 1.1mm and 5mm outer is best.
Also check B tension screw.
Try a brand new cable and outer? Even though you have lubed the existing one this may fix the problem
My Tiagra geared commuter is the same, but my similarly equipped winter roadie is a bit more precise and the shifting just feels lighter.
I think it is due to the commuter being hammered on bridle ways and not cleaned often whereas my roadie gets less mud (ie none) and a bit more care.
I just live with it and as you say "feel" the gears in on changing to larger rear cogs.
Maybe more frequent and better cleaning and lubing will sort it.
Try a new inner cable. 105 shifters are well known to break cables about an inch or so from the nipple end, so it may have already started fraying (sp).
If the cables run on the "inside" of the bars (small radius), unwrap the bar tape and reroute them around the outside (larger radius)
I will practically guarantee that this poor shifting is a result of the final short cable outer before the derailleur having too much friction. It needs replacing. I suspect one of the end ferrules has a small kink that impedes the cable. Before you change shifters, cables, bar tape etc, replace this short cable outer and see if it improves shifting. My Ultegra had exactly the same issue after a full cable change, and no amount of checking hanger alignment (professionally with correct tool), adjusting cables or anything else would cure it. A trip to a nice old guy in a distant LBS when I was away left me £1.50 poorer and with the above tip. It has shifted perfectly ever since.
What Tired said. Did a cable replacement today and the friction in the final cable run was ridiculous, all the others were fine. Shimano sell wee rubber boots for gear cables which can help to keep the crap out.
For what little it cost I don't think its ever worth changing just the inner and not the outer esp on 10 or 11 speed bikes
Thanks guys.
Rode this morning and found it was a lot better after all my tlc. Still not perfect but it gives me hope that there is light at the end of the tunnel.
I'll change the rearmost section of cable/outer next as per Tired's suggestion.