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I have trouble indexing my SRAM Apex 1x drivetrain. If I get it to shift correctly at one end of the cassette, it doesn't shift so well at the other end. Sometimes I have to click multiple times at the DoubleTap shifter to make the rear mech move enough for the chain to jump to the next sprocket.

I have tried the usual, first of all the chain tension barrel adjuster at the rear of the mech. Also, I have tried removing the cable from the mech, changing the tension. And fiddling with the B and limit screws. To no avail.

For context, the drivetrain has recently been moved from a few years old bike to a brand new frame by a seasoned bike mechanic.

Could a slightly bent rear mech cable under the BB be the cause of the poor shifting (see photo)?

And if so, can something be done about it - other than replacing the cable?

Slightly bent rear mech cable

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    Why is the cable slack? – Daniel R Hicks May 8 '20 at 18:58
  • It's on the smallest sprocket, with the least cable tension. – agibsen May 8 '20 at 20:04
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    So in other words it's improperly adjusted. – Daniel R Hicks May 8 '20 at 20:19
  • That's a weird peg just in front of the rear wheel. Is it a kickstand holder, or is it a mount point for a mudguard/fender ? – Criggie May 17 '20 at 21:55
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    @Criggie That's a good question - I actually don't know. The frame is a Cotic Escapade. – agibsen May 18 '20 at 22:06
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No, the 'bent cable' is not causing the problem.

As soon as the shifter pulls the cable the tension of the derailleur springs will straighten it out. It may be slightly bent when first installed but should straighten out in a short time.

The excessive slack you have in that cable indicates something is adjusted incorrectly. Presumably the derailleur is on the smallest sprocket and is resting on the high limit rather than being controlled by the cable and shifter. That would mean your indexing adjustment is off. I'd work through a rear derailleur setup process to fix that problem first. The Park Tool Rear Derailleur article and video is has a very clear step by step process.

If that does not improve your indexing, the next thing to look at is the derailleur hanger alignment.

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  • Yes, I have probably made it worse than before, but since the seasoned bike mechanic didn't manage to get it right and smooth-shifting, something else must be wrong. – agibsen May 8 '20 at 20:22
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    @agibsen - I have found to never presume anything about a bike mechanic, seasoned or not. Some say I am a cynic - maybe so - but bought on by experiance. Like all industries, it has its share of those are doing it for the passion, and those which it's just a job to earn money. – mattnz May 9 '20 at 0:27
  • Find a bike mechanic who is not beyond his best-by-date. – Carel May 9 '20 at 7:34
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If it's not excess slack then hanger alignment is always the first suspect.

The bends in the cable you can see shouldn't cause problems, but seeing them on a Doubletap bike makes me instantly suspicious of kinks inside the housings, which will wreck the shifting. While avoidable, it's easy to have this happen with Doubletap levers by nature of how you install cables into them, especially if existing tape is being left in place.

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Problem solved!

After having replaced both the bent cable and the cassette, the shifting was still causing trouble.

But then I checked the chain length. It turned out it was shortened too much: Only a three link overlap (measuring by routing the chain over the biggest sprocket and the chainring bypassing the rear mech).

SRAM recommends a four link overlap.

After having replaced the chain and added a five link overlap (one of them being the PowerLock), the shifting is now nearly flawless!

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