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Discussion Starter · #1 ·
Hi

Have an ongoing problem with my rear (Chorus) derailleur. New cables, new chain, new cassette, but it just won't shift "down" (large cog to smaller cog) properly, especially on the biggest half of the cassette.

Shifting the other way is fine (small cog to biggest), but going down, it simply won't go into gear most times. Usually, I either have to give it an extra nudge with the thumb leaver, or go down an extra cog and come back up.

What it feels like is that either a) the cable is not releasing, so the derailleur isn't pulling back across, or b) the derailleur itself isn't pulling the chain across enough when I shift down.

Local LBS (a good one), have checked derailleur and think it's fine. But this is ridiculous. I have 2 bikes, one with Centaur, one with carbon chorus, and the Centaur one shifts fine.

Note that this is not a barrel adjustement problem .. all that is fine.

The one caveat here is that I'm running a 13-29 cassette on a short throw derailleur. Not entirely kosher, I know, but I can't believe that it is the cause of this. (Also, on other bike, same cassette/derailleur combo works fine).

Any help appreciated. Thanks.

B
 

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cycling as lifestyle
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ok, but still it is a short cage on a 13-29 cassette. What I would suggest is to go to your LBS and ask them to install a long cage rear derrailleur and see if that fixes the problem. You can try your bike in a parking lot, any differences should become quickly apparent. If this does not fix it, I would check all the ferrules and bushings that came with the cables. If that still doesn't fix the problem, then it is most likely the ergo shifter and not the derailleur.
 

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You say it's happening on the "biggest half of the cassette" - and you're using a short cage derailleur (rated for a max of 26T).

I know you don't want to believe this is the problem, but it is. You don't have enough chain wrap, the cage is sitting BEHIND the cogs (rather than underneath them), and not getting enough leverage to move the chain.

Buy a medium cage (just the cage - not a whole new derailleur) - swap it out, and it will ship as it was intended.
 

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yanksphan said:
You say it's happening on the "biggest half of the cassette" - and you're using a short cage derailleur (rated for a max of 26T).

I know you don't want to believe this is the problem, but it is. You don't have enough chain wrap, the cage is sitting BEHIND the cogs (rather than underneath them), and not getting enough leverage to move the chain.

Buy a medium cage (just the cage - not a whole new derailleur) - swap it out, and it will ship as it was intended.
+1.

You can even use the pulleys and hardware off the short cage.
 

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sure??

Your supposition would make sense for the 29-26 shift (from the big ring), but not the 26-23-21 shifts. Once you're off the 29 tooth, the RD should behave the same as it would with a 13-26 or 12-25 cassette. Some people use a 13-29 with a short cage RD, just by carefully avoiding the 53/29. I wouldn't do it, but as long as you never shift to that combo, then the wrap capacity is never exceeded.

Loosen the "B" screw as far as possible to increase the clearance of the upper derailleur pulley and largest cog.

The OP should first check the chain length and be sure that it is as long as possible. Shift into the little ring and smallest cog. The chain should be just long enough to avoid hanging loose or rubbing the upper pulley chain guide. It's common for the chain length to be set 1 inch shorter than this length. If the chain is 1 inch too short, you lose 4T of wrap capacity.

The next thing to check is the RD alignment.

Most often, refusal to shift to smaller cogs is a cable friction problem, but it could also be a problem with the RD. If the cables have more than a few thousand miles on them, I'd change out the cables and housings.

The OP should also be sure that he understands how to adjust the RD cable tension. Loosen it until the shift from the 13-14 hesitates or refuses to execute, then tighten just enough to resume proper shifting in the 13-17 range. Then see how the shifts to smaller cogs function, in the 29-19 range.
 

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C-40 said:
Your supposition would make sense for the 29-26 shift (from the big ring), but not the 26-23-21 shifts. Once you're off the 29 tooth, the RD should behave the same as it would with a 13-26 or 12-25 cassette. Some people use a 13-29 with a short cage RD, just by carefully avoiding the 53/29. I wouldn't do it, but as long as you never shift to that combo, then the wrap capacity is never exceeded.
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In theory, I agree - problem is, the 26t max is just that - the max. Even when using a 13-26 the short cage derailleur doesn't perform as well as when it gets down into the 23 and 25 range.

The OP was a bit ambiguous though about how bad his shifting really is. I would assume that first shift (29-26) is probably pretty awful (upper pulley too close as you mentioned) - but it probably improves little by little on the way down.

Cable tension was probably compromised as well in an effort to get the derailleur to make the 26-29 shift (on the way up). What I've seen in my experiences at least. I agree though - probably time to check hanger alignment, dropout alignment (wheel sits crooked), etc.
 

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Also have the RD hanger alignment checked/adjusted. Also sounds like a cable friction issue. With the cable off the RD, feel how much tension it takes to pull out when you downshift, if it is excessive check routing and for casing kinks, especially where the cable exits the brifter under the bar tape.
 

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Discussion Starter · #9 ·
yanksphan said:
In theory, I agree - problem is, the 26t max is just that - the max. Even when using a 13-26 the short cage derailleur doesn't perform as well as when it gets down into the 23 and 25 range.

The OP was a bit ambiguous though about how bad his shifting really is. I would assume that first shift (29-26) is probably pretty awful (upper pulley too close as you mentioned) - but it probably improves little by little on the way down.

Cable tension was probably compromised as well in an effort to get the derailleur to make the 26-29 shift (on the way up). What I've seen in my experiences at least. I agree though - probably time to check hanger alignment, dropout alignment (wheel sits crooked), etc.
Yes, it's worse going 29 - 26, the next couple are pretty hit and miss, and from then on it's more or less OK.

LBS also suggested that derailleur was probably sitting too far back, and on last visit, added a link to the chain, and removed, cleaned and added a "special lubricant/friction product" to the cables. Cables are pretty recent (a couple of months old, 2000 km's). Also, LBS believe derailleur is sitting and functioning as it should.

While I accept that what has been posted here is generally accurate re the short cage issue, why is it that on my other bike with the same setup I'm not getting this problem? Furthermore, I've been to the LBS 3 times with this. Each time it comes back fine, but within a couple of weeks has deteriorated.

FWIW, if indeed the problem is the longer range of the cassette, I'd look at changing to a Compact before I moved to a long cage rear derailleur.

Thanks again for the input/suggestions, will double check what I can.

B
 

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frame differences...

One thing that is often overlooked is the difference in chainstay length between bikes. If you're lucky and have the perfect chainstay length, you can gain up to 2T of wrap, compared to the worst chainstay length. Since the minimum increment of chian length change is one inch, or 1/2 inch of chainstay length, there's a perfect length. A chainstay that's 1/4 inch or about 6mm longer or shorter would lose 2T of wrap.

It is wise to use a medium cage RD. It's the most versatile and you'll never notice any difference in shifting. It will handle any compact and most triples, unless you combine a triple with a 13-29.
 

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It sounds like excess friction.
Did you replace the cable housings with the new cables? The housings are at least as important as the cables, if not more important.
The short housing just before the derailleur is exposed to lots of dust, grit, water, mud, etc. If the short housing was not replaced that could be the problem.

Al
 
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