niuoka

older trex 7500 with 8 speed rear. New shamanio chain and rear derailleur small pulleys about 500 miles ago. at that time, I also cleaned and repacked all the bearings, cleaned the cassette and chain ring. No sharks teeth. I commute approx. 100+ miles a week now. ( 9 miles one way to work)

so the other day riding into work, the bike was shifting fine in all gears except between 2 and 3 or so it seemed. the problem is when I am shifting between those two it might be many revolutions of the crank before it will shift. or not shift at all. Other gears shift right away, and I am not cross shifting.

so I got to work, wiped down the chain and shot the rear derailleur ( not chain) with wd40....that's all we had...its not what I would normally use.
I did notice that the rear cable is a bit rusty in looks so I stopped and got a new cable on the way home to try to fix this all this weekend.
on the chains I use chain-L and I use tri-flow on moving parts like derailuers, shift pivots, brake pivots etc.

riding home the wipe down and wd40 made no difference.

rode in today, no difference or fix. so during lunch I looked at the shifters and don't see how to replace cables. they are old shimano alivio click stop shifters. ( cant afford to replace shifters right now if that is your suggestion to fix)
Ill be working on the bike tomorrow ( Saturday)

so questions
1) how does one replace the cable in the alivio thumb shifters. in the brief time I have at work, I could not find anything on internet directly related to that style shifter.

2) what is the normal reason for the shifting issue.

Hopefully the new cable and adjustments will fix it. Yes the bike is old, but in really good shape and was bought used with super low miles in march.

wmodavis

Usual reason for delayed shifting in my experience is cable not properly tensioned.
But that being said a lot of things can contribute such as friction between cable and housing, derailer hanger misaligned, properly adjuster derailer, etc.
To have flawless shifting all has to be right.

AnkleWork

1. Probably shift into high and push the inner out through the small hole in the *shifter body*.
2. Maybe frayed cable near the shifter.

cny-bikeman

1. Did you think to Google replace the cable in the alivio thumb shifters? First three results are Youtube videos and Shimano Tech Docs link.

2. Multiple reasons. Logically, if the problem is always just between those two cogs (no matter what chainring?) then it has to be something related to the position of the cable or lever. So that would mean a defect in the cable or some sort of obstruction or damaged part at the shifter that come into play at that time. Shift between the two by pulling and releasing the shift cable with your hand. If it still hesitates then it's the cable. If not then shift lever.

Al1943

Probably excess friction between the cable and its housings.

cny-bikeman

It's likely to be more than just friction if the problem only occurs between two gears, especially wnen not at either end of the range.

niuoka

thanks for the constructive reply. I was at lunch using my bosses computer and had limited time b4 posting. Not every one has a job where they have acess to computers, we are not even allowed to have our cell phones with us. I had limited time, and did google it, but did not see the youtube ones pop up. But now that I am home, I have and they do help.