Shimano STI does not shift up/to lower cogs

Question

Typ: Shimano RS505 2x11 hydraulic

Problem: Up shifting is possible to the 5th or 6th cog, after this the STI does not give the click feedback and the derailleur does not move to the next smaller cog. If the cable is under more tension the STI shifts normaly and makes a proper click on every shift. The derailleur is cleaned and has full tension in all positions. I tried a different derailleur and got the same result.

When did the problem occur: After a muddy tour the shifting got worse and inaccurate. Today I cleaned the bike with pressure water. I was always far enough away from the STIs, but maybe some water got into it. After that the derailleur started to stuck.

What did I try so far?: I pulled the rubber hoods down and put some grease into the STI, however it did not get better yet.

Any chance to repair the STI?

Answer 1

Sounds like the shift cable have become contaminated by grit or mud and are hanging up or there is excess friction, which stops the derailleur pulling the shifter onto the next highest gear position.

When you give the cable a little extra tension it overcomes the friction allowing the shifter to shift properly.

You can try removing the shift cable from the housing, cleaning and lubing it. If that does not fix the problem you can replace the housing. Start with the section at the derailleur end as it is closest to the ground an has the highest chance of getting something in it.

Answer 2

This is also a symptom you will get if the shift cable frays where it enters the shifter.

The cable bends as it enters the shifter, and it can fray there as the constant bending and unbending as you shift stresses the cable over time.

With all the Shimano shifters that I've deal with that had under-the-bar-tape shifter cables, the channel where the shift cable enters the shifter body itself is visible from the top of the shifter after you pull back the rubber cover. I don't have experience with the RS505s, but the engineering documentation from Shimano seems to show the same visible shifter cable channels in the drawings.

Pull the shifter cover up and look at the top of the shifter body near the where it meets the handlebar. Hopefully whoever did your bar tape didn't run the tape high enough on the shifter body to hide the shift cable channel.

You should be able to see the shift cable in the channel.

Is it frayed?

If so, replace the shifter cable.

It's also a good idea the check the cables in this location occasionally, as a cable can fray without any symptoms. And once it starts fraying, it's much more likely to snap.

You do not want to have to ride home with your chain stuck on the 11-tooth cog, especially if you have some good hills to get over on the way...