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All new 9-speed drive line skips/jumps on 18T & 21T cogs -

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All new 9-speed drive line skips/jumps on 18T & 21T cogs -

Old 05-17-16, 12:53 AM
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TacomaSailor
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All new 9-speed drive line skips/jumps on 18T & 21T cogs -

I’ve been riding seriously for almost 50-years and do almost all my own maintenance – on dozens of bikes. Every time I get a little cocky and think I know what I am doing a bike jumps up and says “Not a Clue – Dude.”

Stumpjumper Comp (2000) hardtail with Manitou elastomer front shocks
XTR 9-speed rear derailleur
Deore LX Rapidfire 9-speed shifter
All new and carefully adjusted drive train (details later)

PROBLEM DESCRIPTION
Rear shifting is now (after all the new installs) excellent on my bike stand and works perfectly on the bike while riding. BUT, When the chain is on the middle cogs (18T & 21T) and a heavy load is put into pedals; the chain skips on the cog OR, occasionally, shifts up OR down one cog. This only happens when accelerating moderately hard from stopped or when trying to accelerate hard on steeper hills.

And, occasionally when on the middle cogs and going over a sharp bump, e.g. off the curb, or small log or rock, the chain shifts down one gear.

The top three and bottom three cogs are perfect under load and the middle three cogs work fine when spinning, even spinning hard.

Here is how I got the bike into this state:

Drive train was working well but shifting was getting a little sloppy and slow and I enjoy maintenance so I decided to update the whole thing.

Took the XTR rear derailleur off (it has about 10,000 miles on it) and cleaned everything. I then lubed all the pivots and ensured everything moved smoothly and easily. The spring tension seemed plenty strong.

All the following parts are NEW and were installed together on Sunday:

derailleur hanger
SRAM PG-950 9-speed cassette 11T – 32T (14T – 32T cogs are fixed)
SRAM 971 9-speed chain (with same # links as old chain)
Shimano XTR jockey pulleys
Shimano cable
Cable housings & ferrules with gentle radii and straight line exit/entry

I have several documents from Shimano manuals showing all the adjustments, settings, measurements, and mounting instructions. I tried to follow them precisely.

I verified the derailleur / hanger angle & mount was as shown in manual

I verified the B-screw setting was 4 – 5 mm as shown in manual (jockey pulley to 32T cog)

I adjusted cable tension to allow smooth shifting from 11T all the way to 32T

I set hi/low adjustment to ensure safe stops but complete range of motion

I verified the jockey pulley is vertically in line with both 11T and 32T cogs

I’ve verified the jockey wheel and 18T / 21T cog are in vertical alignment

I fine adjusted shifting so chain, when on 2nd cog (12T), just barely moves and makes a little noise when shift lever is lightly depressed

I trued the rear wheel and it has almost no wobble in either axis

Specialized hub in rear wheel is smooth and true

While on bike stand the shifting is smooth, quick, and precise. Chain is centered on each tooth after the shift. Spinning the chain slowly on the center cogs shows everything to be smooth with no catches or bumps on any link.

I’ve spent several hours fine tuning, checking, rechecking, measuring, and adjusting but can’t get the autoshift under load out of the system.

What have I done wrong? What should I do to make it right?

Last edited by TacomaSailor; 05-17-16 at 12:57 AM.
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Old 05-17-16, 01:34 AM
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My first guess would be ghost shifting. Is there some frame movement, twisting, under hard pedalling that could affect cable pull, or length?
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Old 05-17-16, 06:33 AM
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Since you have checked the obvious multiple times, you need to check the unobvious (made up word here).

Check cable routing.
Make sure every ferule is seated correctly.
Check the housing is fully inserted into each cable stop.
Make sure the cable and housing are fully seated in the shifter.
Really inspect the cables and make sure it didn't fray during the installation.
Made sure the jockey pulleys were installed correctly, floater on top etc.
Check the side plates of the chain of the chain to ensure it is a 971. You never know wrong packaging.

If all those are up to snuff, then you really need to think shifters and rear derailleur or hopefully someone else has better ideas.

Good luck.
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Old 05-17-16, 06:44 AM
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First, make sure the rear wheel is in the drops correctly. Don't know how many times I've had a bike apart and replaced the rear wheel while on the stand and then found it wasn't fully down in the drops.
It would be nice to check the hanger with the proper tool.
I'd change the housing - looks like you already changed the cable.
And last, I'd try a different cassette. Had one bike that started hunting in the middle gears after being disassembled, couldn't find the problem. Replaced the cassette and it was perfect. Still can't figure that one out.
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Old 05-17-16, 07:05 AM
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Did you check the derailleur hanger alignment? That doesn't have to be off by very much to cause that kind of problem and it can do it in just one or two rear cog positions too.

Frankly, I'm having a similar issue myself. In my case it only happens on the road and only in the biggest rear cogs on steep climbs. In my case I have a stick frame recumbent and I suspect the problem has to do with frame flex. When I get tired enough of it acting that way I think that I'll run a long section of cable housing all the way down the frame to keep any frame flex from affecting the shift cable length.
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Old 05-17-16, 02:24 PM
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I said:
All the following parts are NEW and were installed together on Sunday:

derailleur hanger


I verified the derailleur / hanger angle & mount was as shown in manual


Several of you mentioned torque which made me think some more. I checked the two derailleur hanger bolts and found that one of them had sheared off. When I put in the new hanger I cheaped out by using the old bolts. I guess one of them was weak and I might have torqued it more than necessary.

I installed new bolts and now everything works perfectly. No autoshift and still have nice crisp gear changes.

It still amazes just the little tiny, almost imperceptible, movement of the derailleur hanger can ruin the drive train operation.

Thanks for the suggestions.
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Old 05-17-16, 05:58 PM
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I am glad it worked out for you and you found your answer.

Also be aware than even that many "new" derailleur hangers are not straight and need to be tweaked after installation. You got lucky
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