Hi,

This is a follow-up from my thread from yesterday:
http://forums.roadbikereview.com/showthread.php?t=125423

After replacing my 11-23 with an 11-27 (minus the 16 sprocket), rear shifting does not work as well as it did.

What happens is that when downshifting (moving towards bigger sprockets), the first 4 shiftings are OK, but then, nothing happens even though I shift twice, and by the next shifting, the chain jumps to the correct sprocket.

Upshifting works great.

I checked that my chain is not too short, and I get from Sheldon Browns site that I should trim the indexing adjustment and the B-tension adjustment (running an Ultegra-SL).

So, not being a first class wrench, my questions are:
1. Why is this happening?
2. How can I adjust this (clockwise or anticlockwise)?

Cheers!

/Max.

OK, so your cassette is now 11, 12, 13, 14, 15, 17, 19, 21, 24, 27 right?

Make sure you're using the 11 lockring and that it's torqued to 40Nm. The cogs should not wiggle or move at all on the freehub.

Next thing to do is double check your spacing by using a spare spacer as a feeler gage. It should fit exactly between every pair of cogs.

Done! (correct lockring, no wiggle and correct spacing). Still the same problem at this point.

Sometimes, the chain jumps back to the correct sprocket after 2 shiftings, sometimes after 3. And never close to either the smallest sprocket or the biggest. Always in the middle. Sounds very bad when I shift...

Anyone with advice about indexing and b-tension adjustment, or whatever the problem could be? I'm planning a nice ride tomorrow, and would hate to have to take the bike to my LBS...

Done! (correct lockring, no wiggle and correct spacing). Still the same problem at this point.

Sometimes, the chain jumps back to the correct sprocket after 2 shiftings, sometimes after 3. And never close to either the smallest sprocket or the biggest. Always in the middle. Sounds very bad when I shift...

One more thing... You did put the 1mm spacer behind the cassette?

After that, I do not know what to tell you without looking at it. Put it back the way it was for your ride tomorrow! :)

Yes, I did put the spacer behind the cassette.

No, I won't put the old one back. I'd rather put up with the shame of bringing it back to my LBS :p

Anybody with new ideas?

Just speaking hypothetically here, since I don't have your cassette or one similar in front of me. The cogs have different tooth profiles and notches cut into them at specific intervals that act as "shift ramps" to help the chain make the move to the next larger cog or more easily release to the next smaller cog. By removing one of these cogs you have now disrupted the ramp profile. The angular relationship from one cog to the next is set specifically so that the teeth align with the spacing of the chain links. Again, by removing one of the cogs, this disrupts the pattern. I suspect this is the cause of your shifting issues.

Did you put one or more of the cogs on backwards?

The way I have taken care of this problem before is shift to the 15 (the one you are in after the four downshifts) and then turn the adjusting barrel (I believe counterclockwise), while turning crank, until it shifts to the 17. Then turn the barrel the opposite direction until it just shifts back to the 15. Then about a quarter to half a turn more. This will usually get rid of any noise I have had. Then test the shifting going through each gear.

This is what I have done when I have a particular gear that is giving me problems. After this adjustment all the others seem fine.

Monte

The way I have taken care of this problem before is shift to the 15 (the one you are in after the four downshifts) and then turn the adjusting barrel (I believe counterclockwise), while turning crank, until it shifts to the 17. Then turn the barrel the opposite direction until it just shifts back to the 15. Then about a quarter to half a turn more. This will usually get rid of any noise I have had. Then test the shifting going through each gear.

This is what I have done when I have a particular gear that is giving me problems. After this adjustment all the others seem fine.

Monte

Brilliant! I did pretty much exactly what you said and it worked! Well, not the 1st time, some other gears got affected, but I reused the same method and now all my gears worked perfectly! At least on the stand...

And more important, I now have a better understanding of how the rear derailleur can be adjusted in case (aka when...) I get a problem!

Thanks!

PS1: No, I hadn't mounted on the cogs backwards.
PS2: Cyclo-phile: Yes, I'll have to check when riding if there's some kind of difference in shifting down from 15, or up from 17 because I got rid of the 16.

As already mentioned, it's the cog timing that is fouled up. I did the same thing with a Campy 13-29, taking out the 16 and made a 12-29 using cogs 12-15 from another cassette. The 15-17 shift was not good at all and never will be due to timing problem.

Did you put one or more of the cogs on backwards?
They won't go on backwards. The small off-center spline won't line up. - TF- TF