the sci guy 

So I just put a new chain on my bike, and every once in a while - usually while I am pedaling with force up a hill or shortly after - it seems to release / jump like it's switching gears on me but then goes back to normal (it doesn't skip to another gear). Is this a chain issue, a derailleur issue, or a cassette teeth issue? (It also randomly seems to bind up hard sometimes making that lovely grinding clung! sound)

Thanks

jyl

Worn cogs would cause the skipping. Not sure about the binding.

cyccommute 

Yup. You need a new cassette (or freewheel, whichever you use).

arex

Sounds like the chain is slipping a tooth. This would be wear on the chain or cassette, maybe the chainrings, and/or the chain is stretched. If the wear is bad enough, you'll need to replace the chain and cassette together. If the chainrings are badly worn, they can be replaced or just flipped over so the non-worn side of the teeth is driving the chain.

Someone else can probably explain this better.

fietsbob

'Sci guy' should do A scientific analysis, first .. or old school mechanics , replace questionable parts. (pre-internet)




Few chainrings can be simply flipped over any more , due to shifting aids on one side.

corrado33

Check and make sure you didn't bend a link in the chain. I somehow did that on my mountain bike and it'd skip but not shift gears.

cny-bikeman

No, a tight link can show up under low pedal pressure, and only at certain points in the rotation. The tight link will be at the rear only once per 2 revs or less.

bigredkevbot

Could be the stretch/spacing on the cassette/freewheel/cogs. It could also be an indexing issue (rear mech cable tension). I would loosen your cable maybe a quarter (1/4) to a half (1/2) turn and see if that resolves the issue. How long were you running a stretched chain? If it was the rear cogs/gearing it will likely wear out your new chain very quickly.

corrado33

I never said a tight link. I said a bent/twisted link.

the sci guy 

It's the first time I've ridden the bike in over 15 years. (Pertinent thread here: https://www.bikeforums.net/commuting/...-thoughts.html
I never replaced the chain when I was originally riding it in the 90's (because I was a kid in middle/high school and didn't know such a thing), and I don't feel like it was ridden enough to wear down the cassette that badly. But, I mean, anything is possible.
This past weekend I put on the new chain, after cleaning the hell out of the entire drivetrain. I did not adjust the cables or the derailleurs though because they still shift perfectly and also I don't know how. The cables need to be replaced since they are original but I'm mostly still shaking the jitters out of the bike before doing too much overhaul.

I will take a few pics of the cassette teeth before I commute home and post them here for y'all to take a look at.

Thanks everyone.

cny-bikeman

Pics are not likely to help, as the wear is often not discernible to the naked eye. This is a VERY common problem, and it does not take much riding on the small cog (even with the small chainring) to cause enough wear to skip on a new chain. If you are a scientist then you understand that diagnosing a problem requires logic first. The only thing you changed was the chain, which as it is new is unlikely to cause the problem. The problem occurs only when high force is applied, and the part that is experiencing the highest force is the rear cog, due to having the fewest teeth. Therefore one would logically conclude that the cog is the problem.

BTW, another basic tenet of science is the necessity to gather and convey all the relevant information before making an analysis. I am unable to fully answer because you have not indicated in what gear combos the problem occurs.

habilis

Your chain does not actually change to a new cog but may be trying to do so. Is the derailleur straight, meaning hanging straight down in a line parallel to whatever cog it's under, and parallel to the rear wheel? Sometimes the derailleur and/or its hanger get bent, usually inboard toward the wheel. If so, check back here on how to proceed.

Also, are you cross-chained (big-ring-big-cog or small-ring-small-cog) when this problem happens? I've had terrible shifting problems when I do that.

cyccommute 

No. Sci guy's chain isn't trying to change to a different cog in the rear. This is a well known and common problem when using a new chain on old cogs. The chain is actually riding up and over some of the teeth on the cog and failing to engage. The edges of the cog's teeth are rounded and allowing the chain to disengage as pressure is put on the chain. The chain isn't moving to the side as you'd expect if the hanger is bent. This video shows a skipping chain quite clearly


You can clearly see that the chain isn't moving from side to side.

FastJake

Jumps in the smaller or favorite cogs only - cassette/freewheel is worn and needs to be replaced.

Jumps in all the cogs including the largest cog - probably a RD adjustment issue. You can verify this by pedaling it slowing by hand in a bike stand. You will see it skip as the chain moves from the upper RD pulley and doesn't hit the cassette cog properly.

Gosh darn kids with their internet that don't know nothin' these days! (Kidding, and I'm 25 years old...)

Poonjabby

Did you put the chain on the right direction?

Poon

Homebrew01

In some cases, if the skipping is mild, you can "live with it" until the chain wears a bit and the skipping might go away.
Replacing the cassette or freewheel is likely the better option.

FBinNY 

new chain on old sprocket is prone to skipping under load. If it's a RARE occurrence on only a single sprocket, and you can live with it a little while, it will cure itself over time. But if it nearly always skips under load, you won't have the patience to wait for it to resolve and need to replace the sprocket (usually the entire cassette)

davidad

Simple explination. Chain care, wear and skipping by Jobst Brandt

the sci guy 

On the largest chainring, and usually the bottom 3-4 small cogs in the cassette. I use the middle 2 the most (4&5 out of 7). Also I'm not a scientist, just a huge Bill Nye fan.

Also, since you're a fellow Syracuse guy, you may enjoy where I originally bought my bike:


Also here is a pic of the cassette for ****s & giggles - best I could do in the dark garage (i didn't remember until tonight)


Only seems to happen in the two gears I use the most - I'll admit I don't use the larger cogs because I don't need them - Houston is flat.

If it will self correct, that I can live with it for a little while. It's not constant and it's not that bad - just surprising when it happens.

velocentrik

A very long time ago I had my first "good bike." It was a steel Trek. After gobs of miles, it started skipping too. I took it to good bike shops and they diagnosed that it needed tuned, then it needed a new cassette. In the end, it was simply that my middle chainring was worn. I still can't believe they didn't figure it out. I was out the cost of the new cassette on the bike and still needed a new ring.

cyccommute 

Yup. Classic worn cassette with a new chain.

I doubt that it will self-correct anytime soon. It may even get worse. And the chain skipping across the teeth of the cassette may damage the chain. 7 speed cassettes can be had for around $15. Just change it.

FastJake

+1 Get a new cassette. It costs only a little more than the new chain you put on, so why ruin the new chain with a junked old cassette?

the sci guy 

I've never bought a cassette outright - care to recommend a quality budget one (brand?) (links?)

Also what tools do I need in order to do such a thing? I know I could google it but sometimes people do it differently and it's good to hear different input.

FastJake

Shimano or SRAM. Like the two below, for example. I haven't ventured into the bargain bin of Sunrace and other, cheaper options. But 7S cassettes are so cheap to begin with that I haven't bothered. Fancy expensive ones are long out of production so your only option is a cheap one. Just don't get a freewheel! Sometimes they are mislabeled as cassettes or labeled both for some reason. This is extremely bad practice but it's something to watch out for.

Shimano CS HG20 7 12 32 7 Speed Bike Cassette Road Mountain Hybrid Bicycle | eBay

SRAM PG 730 12 32 7 Speed Powerglide II MTB Bike Cassette Chrome Fits Shimano | eBay

Changing a cassette is easy. You need a chain whip, a lockring tool, and a wrench to turn the lockring tool.

Google is your friend, this isn't a difficult operation.

cyccommute 

A Shimano HG20 should cost you less than $20-$30 at a shop through QBP. Nashbar has a PG-730 for $16, although that one is a 12-32 which is geared lower than your current cassette. Yours looks like it's a 12-28 which is on the higher end of the spectrum from QBP.

You'll need a Park FR-5G lockring tool which costs around $10. There are other tools that are similar and cost about the same if you can't find the park. It's easiest if you have a chainwhip as well. The Park one is a little expensive compared to others ($25 vs less than $10). Or you may be able to hold the gears in place with a rag and loosen the lockring. I find the rag thing to be more difficult than just getting out the chain whip.

It really easy job to do.