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ghost shifting

sundial2010-04-28 20:29:39 +0000 #1
I just finished a ride in which my chain was busy chatting with the 50T cog and the derailleur or chain or cassette decided to play switch and slip when I used 34T and the 3rd highest gear

I've measured the chain and it's not stretched out. I had the front derailleur adjusted because I was losing the chain between the 50 and 34 cog, whether I was shifting up or down. Now the rear is jumping from the 2nd and 3rd highest gear even though I've adjusted the rear derailleur. The teeth on the cassette do not look worn and I don't see any light between the chain and the cassette.

I have a SRAM OG 1070 11-28 cassette. Is this the nature of the beast? Do I need to replace anything? I have had this bike for a year now and put about 4000 miles on it. Thanks in advance.
aicabsolut2010-04-28 20:32:30 +0000 #2
What do you mean by "jumping"? Do you mean the chain feels like it's skipping on top of the cog or is the chain trying to jump between cogs and not settling on any one cog?

The first is "skipping," and the second is "autoshifting."

Skipping: sheldonbrown.com/der...stment.html#skipping

Autoshifting: www.sheldonbrown.com/autoshift.html

Alternatively, your indexing may be off. Does it happen such that you have a hard time shifting up or down into that problem cog? If so, then it's an indexing issue. If you can shift fine but then it starts acting up under load, then it may be one of the other problems.

If indexing improves things some but not enough or not for long, then check the condition of your cables. Any obvious damage to the cable or housing? Is it really dry under your bottom bracket? Try lubing the cables under the BB. If nothing works and you're certain it is not a chain wear problem, then you might need to replace your cables. Since you had some issues recently with the FD as well that sounds like a cable tension problem, my guess is that your cables are just getting too old and need to be replaced. That's not surprising at the year mark with the mileage you've got. DA cables might last a bit longer (because they're thicker) but it's probably a good time to change them, particularly if they are not Dura Ace cables.
DebW2010-04-28 20:53:12 +0000 #3
If you have 4000 miles on one chain, then it's time to replace it. 2000 miles is a more reasonable replacement time. You may have to replace the cassette as well as the chain to avoid skipping.
sundial2010-04-28 20:55:44 +0000 #4
Quote:

Originally Posted by aicabsolut

What do you mean by "jumping"? Do you mean the chain feels like it's skipping on top of the cog or is the chain trying to jump between cogs and not settling on any one cog?

Both. I don't have any problem shifting, but the chain wants to ghost shift over the cassette. Thanks for sharing the links and I'm going to meet with the lbs mechanic and see what we can do to fix the problem.

I guess a new chain and cassette is a small price to pay.
aicabsolut2010-04-28 21:33:49 +0000 #5
I had my shifting go all to hell when my cables quit on me. Eventually, it would get where I'd lose pretty much all tension on the cables and I couldn't get into any cog in particular. The large end of the cassette was the worst, because that's where you need the most tension on the cable. After 6500 miles on one cassette and chain, it never got that bad. I did have issues in just a couple of cogs when, after a really mucky ride, I cleaned my bike too well and had too much friction going on with the cables under the BB. The chain and cassette were fine. Lubing the cables fixed that.

4000 miles is probably near the end of the chain's life. If the chain checker is still good for sure (on the smallest measurement side), then I'd look to the cables. It could ultimately come down to being time to replace everything. Your cassette might still be fine--they can check that with the chain whip thing. Chain and cables replacement would be the cheapest way to start.
ridebikeme2010-04-28 20:50:03 +0000 #6
If indeed you have 4000 miles on your chain/cassette, then take Debs advice and replace both. Do NOT replace one without the other; you will simply cause even more problems. It does sound like a cable tension problem, although with that many miles on your drivetrain, I would replace the chain/cassette and have your LBS check the cables and the housing that feeds into your rear derailleur.
Mr. SR5002010-04-28 20:59:21 +0000 #7
Chain life is all about maintenance, if it's cleaned and lubed it can last for 10's of thousands of miles. Sounds like it just not adjusted properly. I would also have the mechanic check chain length, maybe removing a link or 2 could help. Unless you rarely lube your drivetrain, your cassette and chainrings should be fine. You should go thru 2/3 chains at least per cassette.
Miranda2010-04-28 22:29:54 +0000 #8
Ok, I'm totally humble

here to answer, but since I am having and had this same issue with my mtb I'm putting my vote in for "cables" as the problem source.

The mtb was (and still is) doing the same thing. My kids somehow have the habit of throwing their scooters into the bike rack... which leads me to cursing and preying the bars out of my mtb rear wheel ...

I came here and searched my problem and geeked out good ole Sheldon. For srue I thought it was the derailer. I didn't feel confident enough to adjust on my own, and E-ed one of my guy bike pals w/pics. Needing my bike for the holiday w/e camping trip, I loaded her up to the shop. The tech (and my guy pal wrote back by time I got home) both said "cable stretch"...

The tech didn't even take if off the vehicle rack. He showed me how to adjust it at the bars to tighten the cables. Sure enough it got better. Rode it on a flat at home, was ok. Then when I was climbing hard on the trail... bam, right back. Worst time to happen of course. I about bit it

in the steep drop off as the bike didn't perform as expected.

So, my guy pal says that bar adjustment is for "micro" stuff. The piece towards the back end of the cable is for "macro", bigger adjustment. He said try turning it one way... if gets worse... then go the other until it quits. I'm lucky my suv bike rack makes a great work stand. For ME, I just don't feel confident enough to know when to stop turning the adjustment knob. I guess if you have turned and turned the thing... well, the cables have had all the adjusting they can take before replacement.

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