Sudden strange chain problem(video included)
 

Today as I was shifting between the 9th and 10th(last) cog, applying just slight pressure on the pedals, something very strange happened. The chain suddenly started slipping skipping(whatever is the correct term) on the 10 cog. It now happens all the time, even when the pedals are just slightly pressed. All 9 other cogs work perfectly. I constantly clean and grease my drivetrain, and the chain+cogs are not worn.

Here is a video which explains better:



I thought the H limit screw could've somehow moved so I tried to adjust it with no result. The chain doesn't "climb" on the 9th cog.

I also experimented with the B screw with no result. I also took the wheel off and cleaned the 10th cog and pulleys.


Any idea of what could have happened ? I can clearly see in the video what's happening but can't think of what could be the cause.

Thanks a lot http://forums.mtbr.com/images/smilies/smile5.gif

Put a new chain and cassette on the bike

Chain and cassette have been replaced in January. Chain is not yet .75% worn. 10th cog worked perfectly before, not a single skip. Did you even read my post ?

Yes I did read, and you didn't say you replaced chain and cassette in Jan. You said they are not worn. Cassette looks worn to me.
Have you checked your deraileur hanger alignment?
Don't put bike upside down.

Are you sure that the high limit screw is adjusted properly. On shimano the pulley should a little outboard of center. The chain and cassette wear together and do not skip as they wear. A new chain on a worn out cassette will skip.

I also replaced chainrings and pulleys in January, if it matters. I have a chain gauge, and it shows the chain is not yet 0.75% worn. I don't think the cassette can wear faster than the chain. Regardless, until today the chain never slipped on the 10th cog, even when pedaling as hard as I can. Now it slips all the time, even when pedaling slowly.

Yes, pretty sure. Actually I also tried to adjust it so that the pulley stays quite far on the outside, to make sure the chain doesn't climb on the 9th cog.

Another possibility is to check your cable for fraying or anything that would cause it to stick.

Do you ride in the cog a lot? 11t cogs wear twice as fast as a 22t cog.

It sure looks like a wear issue with the chain and cog no longer being the same pitch. A worn cog does have a different pitch than it started with, and there is no easy way of measuring cog wear directly.

Cable is ok. Inner and outer cable were also replaced in January. However, the cable doesn't really matter, since in the 10th gear it has no tension in it.

The 11t is not quite the most used cog. Also read my previous reply to trailangel. I've had this before, when a cog wears out, the chain firstly starts skipping when pushing hard on the pedals, and then gradually also starts to skip when pedaling with less force. In the current situation it started suddenly skipping all the time.

Chain was lubed yesterday with Finish Line dry lube. However, before filming I cleaned it up with a rag.

I can't help, but kudos for a very good video!

I had read your previous posts, which all have the tone of this one. You sound like you know better and have more experience than anyone who could help you, so you clearly don't need any help from us. Hopefully no one else makes the mistake of trying to.

With I've had this before I was speaking about what was following, the cassette wear namely. Sorry if you got it wrong, english is not my native language.
You're saying the problem is wear. The 10th cog worked perfectly until today, even when pedaling as hard as possible. In a matter of a second it stared slipping even when pedaling slowly. I knew wear causes problems gradually. Is this not true ?

I've followed the Park Tool videos over the last couple of weeks to get my gears shifting smoothly on all my bikes. It might be worth going back to basics and checking everything mentioned in this video:

Anything that wears goes from working to not working at some particular point in time - especially if you only have 11t. You appear to have reached that point. It certainly doesn't appear to be related to the lateral movement of the derailleur and you said you've checked your chain (I'm assuming with a chain checker and not just a ruler). There isn't anything left.

Put a new cassette on. If it goes away, then it was wear. If it doesn't go away, post about it again.

You might also look at a gear chart and see if there is a better gear combination that doesn't have you riding in your highest rear cog as much. Most people only use that cog downhill or when sprinting.

It looks to me like there is a tight link one or two links after the quick link. The "jump" you feel is just the chain remeshing with the cogs. Try pedaling backwards and watch for the derailer to jump in much the same way as the tight link goes through the jockey pulleys.

I don't think there is anything wrong with your derailer adjustment.

Sudden symptom; look for a sudden cause. Bent hanger, bent der, hub bearing failure, loose locknut, an obstruction inside the dropout, etc, who knows. Pull the wheel and touch, feel, listen, look, disassemble, find something obvious.

I checked the links, there are no stiff ones... Also, when pedaling with my feet(not hands, as in the video) the slips occurs continuously, maybe 3-4 times per 360° pedal movement. When pedaling backwards no issue is to be seen.

Today I'll do a complete clean of the area, and also take the cassette and 10th cog out for inspection.

Spring appeard to be ok, I'll look closer today.

Since you are trying or have tried numerous solutions, you could check and see if the cassette is tight to the hub. Use a Park FR 5.2 and make sure it is tight. I know you say there are no tight links but I thought the same thing as the poster above when I saw your excellent video. Do you have an older chain just to check it out?

I also disagree that the cassette or 11 tooth cog in particular is worn. You would have to be riding in that cog everyday for hours since you purchase it to be worn. It may wear twice as fast but I don't believe that most people use an 11 tooth cog twice as much as the others. Good luck.

As I took everything apart yesterday, I found the issue. It was a straw carefully rotated around the groove on the 10th cog, covered with hardened black stuff, making it very hard to notice. I didn't even knew there should be a groove on the cog.
In my first post I said I cleaned the area, but without removing the cogs from the cassette, the stuff there wasn't visible. I cleaned the are between the cogs with a cassette brush but it seems it didn't remove the grime.

Here is the groove which was filled with that straw and black stuff:

http://forums.mtbr.com/attachment.ph...=1208630&stc=1

http://forums.mtbr.com/attachment.ph...=1208631&stc=1


And here is the culprit:


I cleaned the area and entire drivetrain, and now everything works super smooth. Thanks to everyone for helping out !