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Old 10-22-08, 05:02 AM   #1
mesasone
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Chain failure

On the way to work today, I broke my chain. Just fell off as I was starting from a dead stop at a traffic light. I went back to grabbed the chain and carried my bike to work, and then made the walk of shame home tonight. Was not a happy camper.

I'm not really sure what happened. Aside from the outer plates being bent to hell and an indentation on the inner plates, the link looks fine to my untrained eye.





Anybody seen this before? I am a bit concerned if my chain is failing for no apparent reason.
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Old 10-22-08, 05:11 AM   #2
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That happened to me on my new bike ,when at 200 miles, I was learning to shift going up a hill.
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Old 10-22-08, 06:36 AM   #3
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What make and "speed" is the chain? Had a pin been removed and the same pin replaced in the past?
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Old 10-22-08, 08:18 AM   #4
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just buy a new chain,or buy a link and put the chain back togather.
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Old 10-22-08, 10:11 AM   #5
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Carrying a chain tool and a quick link/power link will save you a walk. Looks like something may have gotten jammed in your drivetrain, something as simple as a pebble can do that if it's in the right place at the right time. You might also check your cogs and chainrings for damage.
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Old 10-22-08, 10:26 AM   #6
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Oh, man. All for the want of a chain tool.
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Old 10-22-08, 12:15 PM   #7
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I actually have a chain tool and usually carry one, but had emptied my saddle bag last weekend and neglected to put it back in there.

As for the chain, it is a 9sp SRAM PC-971. No pins have been removed up until this morning when I removed the broken link.
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Old 10-22-08, 12:16 PM   #8
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Yeah. I know that one. I also only get flats when I've neglected to bring my inflator. Also, it rains when I've forgotten to put my mudguard back on.
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Old 10-22-08, 03:01 PM   #9
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No pins have been removed up until this morning when I removed the broken link.
At least one pin had to R/R to mount the chanin on the bike. How much wear is on the chain?

This seems to be a typical failure mode for chains. I perfer to use SRAM or Wipperman links.
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Old 10-22-08, 03:41 PM   #10
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At least one pin had to R/R to mount the chanin on the bike. How much wear is on the chain?

This seems to be a typical failure mode for chains. I perfer to use SRAM or Wipperman links.
Not if the chain has a SRAM or Wipperman link on it.
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Old 10-22-08, 04:08 PM   #11
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Not if the chain has a SRAM or Wipperman link on it.
? How do you figure?
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Old 10-22-08, 04:19 PM   #12
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Not if the chain has a SRAM or Wipperman link on it.


The pushed in/out pin is a weak point in the chain. The other pins have been peened or swedged over on the ends to keep the plate from spreading past the end of the pin.

Remember the extra effort it takes to start to push a pin out when you cut a chain? That's the effort needed to overcome the swedging. Out of line forces, such as a present when the chain line is anything other than dead solid perfect, can cause the plates to spread.
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Old 10-22-08, 04:39 PM   #13
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At least one pin had to R/R to mount the chanin on the bike...

The pushed in/out pin is a weak point in the chain. The other pins have been peened or swedged over on the ends to keep the plate from spreading past the end of the pin.

Remember the extra effort it takes to start to push a pin out when you cut a chain? That's the effort needed to overcome the swedging. Out of line forces, such as a present when the chain line is anything other than dead solid perfect, can cause the plates to spread.
Uh, he said "it is a 9sp SRAM PC-971," and that no pins had been removed (so none could have been replaced). He is obviously using the SRAM PowerLink which came with the chain.
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Old 10-22-08, 05:08 PM   #14
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Yep, this chain has a PowerLink on it, which is what I use when I remove my chain.

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Old 10-22-08, 05:10 PM   #15
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He is obviously using the SRAM PowerLink which came with the chain.
Ah, but I did not make that assumption. If that is indeed the case, beats the heck outta me why it at that link. Maybe some past twisting?
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Old 10-22-08, 05:40 PM   #16
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Ah, but I did not make that assumption.
It's not an assumption. It is the only logically consistent conclusion.
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Old 10-22-08, 06:12 PM   #17
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Chains

I never broke a chain until I went to 9sp. I have broke two 9 spd chains so far. I don't care to start a war here, but I broke both 9 spd chains while powering up a hill on tour. I did not break the chains on the same tour either. Like I said, I never broke a 7-8 spd chain while on tour or any other time. Might just have been my time. I always do regular maintanence on my bikes so the chains were not ignored. Just my opinion!
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Old 10-22-08, 06:15 PM   #18
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This just happened to me on Saturday night as well. Same chain, same bike (assuming it was your lht). I had just had my one month tune up last week and hadn't ridden much due to rain, so I was stoked to be out on a longer ride on sat.
Lbs said they removed a kinked section when it was in, and on sat the chain kept skipping until it finally just popped off. They replaced the chain, so I'm hoping it was just that, but I haven't had a chance to go for a good ride yet due to the weather again.

The guy at the lbs said that from the looks of it, it was a defect.
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Old 10-22-08, 06:25 PM   #19
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There's only 3 reasons why a chain should break.

1) Extremely worn
2) Damaged/twisted chain
3) Installation error

By far #3 is the culprit for people who actually maintain their bikes.
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Old 10-22-08, 06:37 PM   #20
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There's only 3 reasons why a chain should break.

1) Extremely worn
2) Damaged/twisted chain
3) Installation error

By far #3 is the culprit for people who actually maintain their bikes.

#3 is probably the most common, but there are, as someone mentioned above, ways to damage a perfect chain while riding (shifting under extreme load, chainsuck, debris caught in chain) meaning that @ 2 is very likely as well - probably more likely if there was more than a couple hundred miles on it when it broke.
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Old 10-22-08, 07:32 PM   #21
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So, how many miles on it?
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Old 10-22-08, 07:44 PM   #22
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So, how many miles on it?
This is a worthless metric for chain wear. That's why we have 12" rulers.
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Old 10-22-08, 08:55 PM   #23
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I've broken a SRAM PC-951 with less than 100mi on it. Same break. I had used the PowerLink and had no reinserted pins.

I was going up the steepest part of a hill that averages 10%. Guess 200# = too much for SRAM.

My LBS gave me a new one no questions. SRAM will stand behind it, but they shouldn't break.
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Old 10-23-08, 03:50 PM   #24
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#3 is probably the most common, but there are, as someone mentioned above, ways to damage a perfect chain while riding (shifting under extreme load, chainsuck, debris caught in chain) meaning that @ 2 is very likely as well - probably more likely if there was more than a couple hundred miles on it when it broke.
+1
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Old 10-23-08, 04:15 PM   #25
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hmmm... if there was a power link that could be used for chain "breaks", that would almost rule out that someone used a chainbreaker and didn't drive that pin far enough back into the side plate. i've seen that one a few times, and untill you break a chain riding a single speed with full fenders and ONLY a coaster brake going down hill, you haven't lived yet.

perhaps someone took a chain tool to it b4 and didn't drive the link back in symetrically all the way. could be defective. if you don't fully replace it and decide to mend and reuse, inspect the other link pins to be sure they are properly driven in and symetrical.
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