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Old 04-02-12, 08:56 PM   #1
afd88
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Chain Slipping

I have a Trek 7100 that i am experiencing a little problem with. When i apply a little bit more pressure to the pedals i am experiencing some chain slip. Just wondering what some of the problems could be when this happens. The chain just skips ahead or slips forward as i'm peddling.
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Old 04-02-12, 09:09 PM   #2
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Often a sign of a worn drive train. You might need to replace chain and cassette, and possibly the chain rings too.
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Old 04-02-12, 09:29 PM   #3
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I had these symptoms recently. Ended up replacing the cassette, chain and one ring. (The one most used.)
Try various gear combinations to establish which ring(s) and/or cogs are causing the issue.
I'll bet, at a minimum, you need a cassette and a chain replacement.
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Old 04-02-12, 10:05 PM   #4
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See that's exactly what I thought it is a triple that only had about 1000 miles with a brand new chain! I really trust my bike shop so I didn't think that they would put a chain on that was too long out anything. They just did a complete overhaul on the bike and now I am starting to do my own wrenching after taking the park tool classes at my LBS. After the complete overhaul I didn't expect any problems the big problem is in the 5th and 6th cogs from the small end. Anything else it could be?
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Old 04-02-12, 10:15 PM   #5
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See that's exactly what I thought it is a triple that only had about 1000 miles with a brand new chain! I really trust my bike shop so I didn't think that they would put a chain on that was too long out anything. They just did a complete overhaul on the bike and now I am starting to do my own wrenching after taking the park tool classes at my LBS. After the complete overhaul I didn't expect any problems the big problem is in the 5th and 6th cogs from the small end. Anything else it could be?
You say it's after only 1,000 miles with a new chain. Are the cassette and chainrings the same age, or was the new chain a replacement for an older worn chain?

You can also measure the wear age (stretch) of the chain very easily. Since the chain has 1/2" pitch 24 links would measure exactly 12". However as the pins wear the links can move apart slightly, so the chain will be longer than when new. The guideline for replacing a chain is when it's stretched about 1/16" over those 12" to keep the cassette from getting too beat up. If it's stretched more than 1/8" odds favor the cassette also being toast.

Obviously, if this isn't the first chain, the condition of the one it replaced is a factor, but you can't do anything about it now.
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Old 04-02-12, 10:26 PM   #6
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1) You mention that the chainrings are relatively new (that's what you mean by triple, I take it) - but what about your cassette (rear)? If you have a new chain on a worn cogset, you can get the symptoms you describe.

2) How long ago was the overhaul? I'm wondering if you may need to tighten up the cables and/or adjust your indexing. Your derailleur may not *quite* be getting the chain lined up correctly to engage the teeth on the rear cogs.(This is normal after replacing cables - there's a wearing-in period as everything settles into position. Sometimes referred to as "cable stretch" only they don't literally get any longer!)

3) You could have some localized wear or damage on those two cogs (especially if they see the most use, or you've stood on the pedals particularly hard in those gears). With a cassette it's not too hard to replace a couple of cogs, but a lot of the time it's cheaper to replace the whole thing. That would not necessarily have shown up in an overhaul unless they were specifically looking for a problem in that area.

BTW I am an apprentice mechanic!
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Old 04-03-12, 05:18 AM   #7
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The cassette was not replaced during the overhaul? It sounds to me like the cassette just happened to wear out, and chose now to do it.

Maybe have your shop look at the bike and give a second opinion.
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Old 04-03-12, 05:45 AM   #8
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When I overhauled my chainset I changed the triple and chain but not the rear cassette and it was terrible, i soon changed the cassette and it was like new, after I removed the cassette I compared it to the new one and it was clear the difference in the teeth.

Now when I do a full overhaul I also change all componnts so they are all the same age, a little more expensive but avoids ruining days out by the dreaded chain slip!
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Old 04-03-12, 06:43 AM   #9
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sounds to me like you just need to adjust your rear derailleur cable tension. Fine tuning a rear derailleur takes some practice to get it just right, it's quite possible that all you need to do is adjust the barrel adjuster on the rear dr to get the indexing in just the right spot.
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Old 04-03-12, 06:57 AM   #10
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It happens on the 5th and 6th gears likely because that's what you use the most and they are worn. If you trust your LBS as you said, take the bike back to them and let them check it out.

It could be just adjusting the rear derailleur cable tension as suggested but that usually needs done one time and doesn't change unless it's from "wear" of a new cable.
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Old 04-03-12, 05:58 PM   #11
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I'm a bit tired, so I hope I didn't miss anything above, but have you actually measured the chain to verify that it's the correct length? As the simplest and most obvious possibility, it seems sensible to check this out first, before looking for more complex explanations. Sherlock Holmes used to say that one should never confuse the unlikely with the impossible.
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Old 04-03-12, 06:24 PM   #12
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I'm a bit tired, so I hope I didn't miss anything above, but have you actually measured the chain to verify that it's the correct length? .....Sherlock Holmes used to say that one should never confuse the unlikely with the impossible.
Sherlock Holmes didn't know much about bike chains. Chain length isn't and cannot be a factor. If a chain is to be able to transfer power it has to engage positively with slipping even if the other end is totally slack. If chain tension on the slack side could somehow affect engagement or slippage then there would be tension in the lower loop and the net torque delivered to the rear wheel would be reduced.

So paraphrasing Mt. Holmes, one shouldn't confuse the impossible with the merely unlikely.
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Old 04-04-12, 03:45 AM   #13
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Sherlock Holmes was around during the first really great bike boom. I urge you to read the Sherlock Holmes story "The Adventure of the Solitary Cyclist," if you're not familiar with it. While his own cycling was limited to emergencies, his companion Dr Watson was actually a keen rider, and his standard costume when travelling was the cycling uniform of the day - a thornproof tweed hacking jacket and plus-twos (I believe Americans call them "knickers," which epithet carries a completely different connotation on this side of the Atlantic). And, of course, a tweed cap, which it was de rigueur to turn back to front when "scorching," lest the wind whip it off. I often affect a similar costume myself when on one of my vintage mounts. I consider it my duty to offer some kind of antidote to the rather unbecoming cycling garb one sees so often nowadays.


To return to my comments about the chain, they were prompted by my experience with an MTB we bought for my wife a few years ago. From the beginning, the chain slipped every so often. It had a 5-speed block in back and a triple chainring with indexed shifting. My experience was limited to 3-speeds many years before, and I didn't know why the chain was slipping, but we tolerated it. More recently, having become keen on cycle maintenance, I gave that bike a complete overhaul, in the course of which I checked the chain against Sheldon's recommendations for chain sizing, and discovered that it was significantly too long. The bike was a mail order one from a catalogue store (we lived in the wilds of Wales, remote from any bike shop), and they had apparently fitted the chain just as it came out of the box, without shortening it to the correct length. Fortunately, the chain had taken all the wear, and the chainrings and sprockets were still fine. I fitted a new chain, which I adjusted for length, and the bike now runs perfectly.
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Old 04-04-12, 09:19 PM   #14
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Thanks for all of the input everyone, hopefully i will get a chance to look at it in the next few days in my estimation i'm thinking the cable the cable tension is a little "slack" just going by the fact that the cables were just replaced. Now if i could only find that darn barrel adjuster on this SRAM 3.0 rear derailleur. Like i said brand new at this kind of stuff!
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Old 04-04-12, 09:27 PM   #15
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There you go with the cause - cables were replaced. Cables "stretch" after 100/200 miles. Adjustement of the tension with the barrel knob should fix it.

Do a search on Sram d/r cable adjustment and it will tell you how.
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