105 shifter problem?
 

i have had my 105 triple for about 4 years, with the last 2 years being somewhat more active riding, say ~ 4500-5000 miles per year, so maybe 12k miles on the bike.

about 14 months ago, i replaced the rear derailer

about 2 months ago, i replaced the hanger, the chain, the cassette, and the cables.

the wheel seems to be centered

but, i just can't seem to get good shifting..., pretty much everything that can go wrong does - autoshifting, skipping...

one thing that has just started, is that when shifting the rear derailer, (i have a 12-27 cassette) it goes fine from 27 to 24, but then frequently jumps from 24 all the way to 17, skipping 21 and 19...

it appears that the shifter is usually moving to the correct index spot for the 17, but i'm not 100% sure.

i have played with the tension, and can't get this to go away.

could the problem be in the shifter?

do they just wear out..., or could something have just gone wrong in there?

Shoot WD 40 into the internal mechanism of the shifters. Use lots.
Check the cable routing at the rear derailleur where the cable attaches. If it isn't routed correctly it makes the actuation ratio wrong.
Have you replaced the shift cable housings? This should be done when replacing the cables, especially the short housing at the rear derailleur.

i tried WD 40, but it didn't help.

the cable routing is good.

i'm not sure if the cable housing got replaced with the cables, or not..., i know i did not replace them when i replaced the cables, but the shop might have done it when they replaced the cables.

i guess i could just get new housings, and see if it helps.

but my suspicion is that there is a problem with the shifters - it consistently skips 2 gears when shifting out of the 24

Try WD 40 again.
Check the RD hanger again.
Loosen the cable from the RD, slide the short housing forward on the cable, lubricate the cable where it runs through the short housing.
Clean the cable guide under the bottom bracket.

i did the WD40 again..., but no change...

anyway.., i really don't think that friction in the system can cause the problem i have - my deraillure is moving too freely, not getting stuck...

again.., i try to shift from 24 to 21, but it skips 21, and 19, and goes right to 17. sometimes, it even goes from 24 all the way to 17 - it seems to me that whatever mechanism in the shifter, that should stop it after one gear isn't stopping it - like the index system is worn or broken or something.

Ya I know you did this but you have been turning screws and who knows were things are at now.
If it were me I'd start from the beginning remove cable from RD set low and hi limit screws set B screw also, shift lever all the way down as far as it will go turn in barrel all the adjusters pull cable tight and tighten RD clamp. Remove slack with barrel adjuster shift up one gear if it does not shift turn barrel adjuster till it does check shift up one more it should move up to next gear if not tighten adjust a little adjust till quiet all remaining gears should shift good is everything is OK with drive train.
If you still have trouble its something else hanger again, levers or cables check replace as needed and start over from top.