afd88

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.

JonathanGennick 

Often a sign of a worn drive train. You might need to replace chain and cassette, and possibly the chain rings too.

Scrockern8r

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.

afd88

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?

FBinNY 

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.

Buglady

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!

JonathanGennick 

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.

mattwhi

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!

ryanwood

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.

StanSeven

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.

FBinNY 

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.

afd88

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!

StanSeven

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.