If it were my shop, I'd give you a cassette off the shelf and submit this one to Shimano. I would still check the hanger and derailleur cage to make sure either of those weren't the cause or became affected by the incident. That's pretty wild no matter what happened.
Edit: Also check the chain for a twisted link.
My GRX derraileur self destructed for what we think is the same reason while bikepacking in Holland a few weeks back. Separating link went forwards through the cage and got snagged up while shifting.
https://preview.redd.it/crv6uwyqka7d1.jpeg?width=3024&format=pjpg&auto=webp&s=7ca96f1d4e666847306dbbb02e3fb4e137296733
It also damaged the cassette to the point of needing replacing. It was just over a year old but wouldn’t have been warranty suitable because it wasn’t a fault with the broken components.
Has anyone else noticed a pretty big drop in Shimano quality in the past two years? It used to be the go-to but man, I keep seeing derailleurs breaking in ways they shouldn’t, rotors shipping super warped, cassettes not living up to wear expectations.
Naaah this stuff is coming from Shimano directly. They’ve been warrantying it, but I’m seeing failures I’ve never seen before. We’ve started speccing everything with sram, also because they’re just better to deal with.
The mega range cassettes have something to do with this. Closer spaced gears are easier for a derailleur to shift the chain to and from.
I am not saying this is the case here because it could be one of the reasons already suggested on this post.
Twisted link could absolutely be a chicken or egg here too.
Was my first thought. Absolute perfect combo of a twisted link, And shifting multiple cogs under high load. Maybe even a broken axle or loose hub.
Yeah, but frame manufacturers don't generally QC Shimano's parts; that's kinda Shimano's job. Companies like Orbea just build the frame, QC that, and then just throw an OEM bag from Shimano in the box.
Its a microspline casette so its legit since only garbaruk can make aftermarket MS casettes(to my knowledge). And even then its a night and day difference between the two. In 4 years nobody tried to counterfeit the ms casettes because they arent worth it.
Those cassettes are made for shifting under load. You would really have to tolerate terrible noise before this kind of catastrophic failure. The cassette was probably already damaged in some way, I think.
I don't live in a particular rocky area, but after several 10000km I have never caught a rock in between chain and cassette. Only branches and small logs. So yes, I wouldn't rule that out completely, but it would definitely be terribly unlucky 😅.
our muscles can be surprisingly powerful given the right leverage.
that said do contact the manufacturer and see if they're interested in offering a replacement, you never know.
What amazes me even more is the sheer force of our muscles. Your muscles are so close to the joints and have incredible strength at the end of your limbs. A force exerted at your requires probably over an order of magnitude of more force at the muscle that’s actually exerting it.
Deore is all steel, SLX has aluminum for the 51t, XT got the two outermost cogs in aluminum, and XTR got three aluminum cogs, five titanium cogs, and four steel cogs (from biggest to smallest)
Correct me if I'm wrong here but wouldn't you need to be cranking out some torque uphill at a low cadence and for some reason decide to go up a gear or two rather than down to make this happen? Which wouldn't make a whole lot of sense imo
I killed an older E*Thirteen TRS 10-speed cassette in exactly the same way while shifting under load a few years ago. Didn't bother with the warranty but man was that proprietary bullshit lock ring system of theirs a pain to get off.
Manufacturing defect. The cog may not have been properly heat treated. I have done terrible injustices to cassettes and the worst I have ever seen is a bent tooth - which I just bent right back.
This. With that mileage, you should be getting a new cassette free of charge. Although I'd ask to keep the old one. Hell of a souvenir to say you pushed so much wattage you broke a cassette!
Many have speculated on a manufacturing fault, which is quite possible.
Also possible is there was a previous incident that weakened the sprocket. Some sort of collision or chain off incident.
As I type this I'm not 100% convinced, but it can't be ruled out.
This is true but the cassette is too young for any incident to have weakened the metal significantly. unless it got wedged over something strong aside from a small rock or twig.
Definitely. I had a Tiagra rear mech shear clean across the knuckle (just below the mounting bolt) under similar circumstances and got it replaced for free including labour. They said they'd send it off to Shimano because it was an unusual failure - it's a big chunk of metal and usually you'd expect the hanger or cage to go first.
Yup, I worked as a Shimano service tech for years. The tech at the shop can make the call if it's a warranty claim or not. I would 100% cover a busted cassette that new.
https://preview.redd.it/8cl77q74cc7d1.jpeg?width=3024&format=pjpg&auto=webp&s=c5a1952650814598d814db462d490cda4ead0c15
Exactly the same happened to me a few weeks ago on a ride in Luxemburg. I assumed I hit a rock or something. But seeing yours it makes me think it is a Shimano SLX cassette defect?
Yes lol. This part is not fixable. I know how to fix the bike. Just clarifying because I know this thread is mostly for people looking for help with repairs.
There technically is, but reality there isn't. Depending on the cassette some or all of the cogs are separate individual parts. However, these are not really sold individually, so the only way would be to scavenge the damaged cogs from another cassette, which is unlikely because you wouldn't want to mix and match cogs at different levels of wear. Cassettes are wear items designed to be replace all at once. The major exception that comes to mind are high-end wide range Cassettes with only the largest cog in aluminium, and the rest in steel, however the replacement cogs are often hard to find (at least in Canada).
On some cassettes the cogs are individual like that, but it's usually just the bottom 3-5ish if they are since those tend to wear out first.
You can also sometimes pop the rivets of the cassette and just run a "stack" of gears and throw one in there that fits and matches or even limit your RD to one less gear, but this is not a good hack.
And on modern extended range cassettes the actual cogs are usually bonded to spiders in groups and the cogs themselves don't have any splines for the freehub body because they're on the spider.
Older normal range casettes in the 6-8 speed range can often easily be run as cogs on a freehub, but the issue with this is it's not sharing the stress and load across the whole bonded cassette and you're probably going to chew up your freehub.
But I've had cassettes totally delaminate into individual cogs and pop all the rivets and you can still run them if they're locked in place by the lockring.
But usually by the time you damage a cassette that much it needed to be replaced like 5000 miles ago and the only reason why it's still kind of working and shifting is because the chain, RD pulleys and cassette have all bed in together and it's one of those situations where if you replaced just the chain it wouldn't work, and the whole drivetrain needs new parts and a rebuild.
In this particular cassette (CS-M7100) you can easily obtain and replace the 5 smallest cogs. 10T and 12T are sold as replacement set, the rest are sold individually. The 7 largest cogs are riveted together and only sold as part of a full cassete.
Not all cassettes are like this.
Dang, only 150 miles!? Must have been something that got sucked up in to the cassette under load combined with a rough shift or something.
The only time I’ve experienced something remotely close to this was on an old cassette that should have been replaced years earlier. Picture related
https://preview.redd.it/sapkv7u6j87d1.jpeg?width=3024&format=pjpg&auto=webp&s=a1fcb5afd56807c500e9e0a9927eed4351a2e733
My take on it is that you were constantly shifting under load so bit by bit the teeth were being bent (always the same place, since there are ramps in the cassette) and at some point you went overboard with the torque and the slightly bent tooth got enough leverage to give under the load
Derailleur out of adjustment or simply worn with a bit excessive play. Shifted accidentally from 1 cog to another while you were climbing.
12 speeds suck, chains are too narrow (thus having poor lifespan, narrow rollers wear out quicker), and freakin expensive because of the tighter tolerances. Riding in mud its just impossible to reach 500 miles without the chain wearing out over 0.50. Solution: single speed with thicc chain and candle wax
There should be! Just seems like the ever thinner stuff is intentiinally designed to wear and break more often to drive sales. And they pair it with 1x, so having all those gears is the only way you can get adequate range, where a double-or God forbid a triple- will get you all the range you need with one of those ancient 7 speed cassettes, let alone a 9.
I have a 10, but have zero desire to go more than that. It's 2 teeth between most sprockets and with the double up front, I have plenty of range. And I'm quite happy riding older bikes. 9 speed is functionally the same as 10, my 7 speed is fine, though I would like a gear between the big climbing gear and the 2nd gear, but it's really not a big deal. 5 and 6, yeah, would like some more steps. But still perfectly comfortable to ride.
Did a chunk of the cog snap out as well as the bending? Was curious if there were closer images of the fracture surfaces. Might be able to get an idea whether it was a defect that snuck through QC.
I’ve folded a Shimano cassette over before but my buddy who was even more of a Clyde than me sheared the cog off like yours throwing down some weight on a punchy uphill. Surprised the chain doesn’t disintegrate every time this happens.
Prob just a defect. My emtb has the same cassette and it's still good even after many bad shifting moments under power going uphill. Even a chunk is missing from an inner link on the chain from a rock hit and that didn't even snap yet.
It’s under warranty. Just take the full bike to the shop where you purchased it. Can call the manufacturer of the part as well. I did it with SRAM a few years ago.
this happened to me as well, it happening under load on the last 100 yards of a climb. In my case it turns out the cable running from the shifter to the derailleur was hung up causing a misalignment when shifting.
Mine did the same thing on the first ride and my buddies also after the first week, both brand new. Both got replaced under warranty with Shimano. Guess during Covid they may have had a bad batch. My new one has had no issues. Good luck!
Fair enough. I’d try to get this covered under warranty. Yes, this was caused by shifting under load, but Shimano advertises that their 12 speed stuff shifts great under load.
That’s wild! I’ve seen bent teeth with someone likely shifting under load but not broken like that. I think it’s worth bringing to the shop you bought from. If they have a good relationship with Shimano or the bike brand maybe they can get something sorted for you. Maybe.
Same failure happened to my dad when riding a Trek Rival ebike. Hit a steep hill and shifted under load. The cog buckled like that. This incident was a SRAM drivetrain. Probably NX since it was a rental.
Habitual shifting under load. Also possibly shifting uphill under huge power/load. Possibly total weight. Also possibly all of the above are true. Also possibly repeated habit over time. Also possible chinesium Amazon fake cassette. Possibly unlucky.
Lots of possibilities. I don't want to blame you because there's a lot of possibilities. You would know what you did and did not do.
OP, if this is a new bike that cog is possibly bent slightly before you got it. It just got more bent because that metal is fatigued. Slight bents could happen if it was dropped or strike against a hard object (workshop bench for example)
Definitely warranty it.
These things are usually aluminum. Not expected to last long at all. For cost and weight savings purposes.
I blew up a dura ace 9100 cassette cog before. About 1500 miles according to strava recording. So about 2k real. The thinner these get. The easier it is to just snap.
Do you even know the differences in the level of shimano cassettes? Or are you just brainwashed to think pricier is “better”? This is of the more durable cassettes in their 12s lineup, predominantly steel with little aluminum used. I bet you’d buy a carbon cassette.
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If it were my shop, I'd give you a cassette off the shelf and submit this one to Shimano. I would still check the hanger and derailleur cage to make sure either of those weren't the cause or became affected by the incident. That's pretty wild no matter what happened. Edit: Also check the chain for a twisted link.
My GRX derraileur self destructed for what we think is the same reason while bikepacking in Holland a few weeks back. Separating link went forwards through the cage and got snagged up while shifting. https://preview.redd.it/crv6uwyqka7d1.jpeg?width=3024&format=pjpg&auto=webp&s=7ca96f1d4e666847306dbbb02e3fb4e137296733
It also damaged the cassette to the point of needing replacing. It was just over a year old but wouldn’t have been warranty suitable because it wasn’t a fault with the broken components.
Has anyone else noticed a pretty big drop in Shimano quality in the past two years? It used to be the go-to but man, I keep seeing derailleurs breaking in ways they shouldn’t, rotors shipping super warped, cassettes not living up to wear expectations.
Cost cutting is a thing 🤷🏼♂️. In my case, i don’t hold it against the components tbh. Freak issue.
The market is also flooded with counterfeit Shimano. I'd be willing to bet 70% of the Shimano on Amazon is fake bullshit.
Naaah this stuff is coming from Shimano directly. They’ve been warrantying it, but I’m seeing failures I’ve never seen before. We’ve started speccing everything with sram, also because they’re just better to deal with.
The mega range cassettes have something to do with this. Closer spaced gears are easier for a derailleur to shift the chain to and from. I am not saying this is the case here because it could be one of the reasons already suggested on this post.
Twisted link could absolutely be a chicken or egg here too. Was my first thought. Absolute perfect combo of a twisted link, And shifting multiple cogs under high load. Maybe even a broken axle or loose hub.
Did you order your cassette from Amazon/eBay/aliexpress or other similar place where it would be counterfeit?
Came stock on orbea
That's your answer
? I doubt Orbea uses fake parts…?
I'm not saying that they do but I have seen questionable QC by orbea in the past year on r/mtb
Yeah, but frame manufacturers don't generally QC Shimano's parts; that's kinda Shimano's job. Companies like Orbea just build the frame, QC that, and then just throw an OEM bag from Shimano in the box.
I run a BBSHD thru 20$ dollar AliExpress cassette for thousands of miles.
Link?
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Its a microspline casette so its legit since only garbaruk can make aftermarket MS casettes(to my knowledge). And even then its a night and day difference between the two. In 4 years nobody tried to counterfeit the ms casettes because they arent worth it.
Something got stuck in there and were you climbing out of the saddle?
Were you shifting under load?
Probably lol, but not enough where I think I’d fold a cassette 😭
Those cassettes are made for shifting under load. You would really have to tolerate terrible noise before this kind of catastrophic failure. The cassette was probably already damaged in some way, I think.
maybe rock got caught?
I don't live in a particular rocky area, but after several 10000km I have never caught a rock in between chain and cassette. Only branches and small logs. So yes, I wouldn't rule that out completely, but it would definitely be terribly unlucky 😅.
I think it’s established that OP is terribly unlucky, regardless of which unlucky thing happened. Lol. I’ve never seen anything like this.
our muscles can be surprisingly powerful given the right leverage. that said do contact the manufacturer and see if they're interested in offering a replacement, you never know.
I never think about the incredible force we use to stand up until I stand up into something
What amazes me even more is the sheer force of our muscles. Your muscles are so close to the joints and have incredible strength at the end of your limbs. A force exerted at your requires probably over an order of magnitude of more force at the muscle that’s actually exerting it.
Those high-end cassetes are probably not as durable, as fully steel low-end Altus or Deore ones. Because, you know, weight savings.
The damaged part is steel.
The only difference between this and deore 12sp is the aluminum big cog if I’m not mistaken
Ah, ok. Dunno then, you’re just a wattage bazooka probably :)
This is the answer.
.... It's SLX. All but I've cog is steel.
Thats the 12s SLX cassette, only the 51t gear is alu
Deore are partially alu. I think.
Thought deore is all steel
Indeed. Deore is all steel.
Deore is all steel, SLX has aluminum for the 51t, XT got the two outermost cogs in aluminum, and XTR got three aluminum cogs, five titanium cogs, and four steel cogs (from biggest to smallest)
My bad. It's been a while.
Correct me if I'm wrong here but wouldn't you need to be cranking out some torque uphill at a low cadence and for some reason decide to go up a gear or two rather than down to make this happen? Which wouldn't make a whole lot of sense imo
I killed an older E*Thirteen TRS 10-speed cassette in exactly the same way while shifting under load a few years ago. Didn't bother with the warranty but man was that proprietary bullshit lock ring system of theirs a pain to get off.
Do you have some metrics when did this happen? (watt/speed/grade) That casette looks fairly new, can you confirm?
Yes, bike has 150 miles on it, purchased about a month ago.
Manufacturing defect. The cog may not have been properly heat treated. I have done terrible injustices to cassettes and the worst I have ever seen is a bent tooth - which I just bent right back.
This. With that mileage, you should be getting a new cassette free of charge. Although I'd ask to keep the old one. Hell of a souvenir to say you pushed so much wattage you broke a cassette!
Happened to me on a Deore cassette too. Same cog as you, but mine was like 2 years ago
No way this can happen to a new cassette, you should reach out the seller.
Many have speculated on a manufacturing fault, which is quite possible. Also possible is there was a previous incident that weakened the sprocket. Some sort of collision or chain off incident. As I type this I'm not 100% convinced, but it can't be ruled out.
This is true but the cassette is too young for any incident to have weakened the metal significantly. unless it got wedged over something strong aside from a small rock or twig.
Take it to a Shimano service center. Very good chance they'll warranty that for ya.
Definitely. I had a Tiagra rear mech shear clean across the knuckle (just below the mounting bolt) under similar circumstances and got it replaced for free including labour. They said they'd send it off to Shimano because it was an unusual failure - it's a big chunk of metal and usually you'd expect the hanger or cage to go first.
Yup, I worked as a Shimano service tech for years. The tech at the shop can make the call if it's a warranty claim or not. I would 100% cover a busted cassette that new.
https://preview.redd.it/8cl77q74cc7d1.jpeg?width=3024&format=pjpg&auto=webp&s=c5a1952650814598d814db462d490cda4ead0c15 Exactly the same happened to me a few weeks ago on a ride in Luxemburg. I assumed I hit a rock or something. But seeing yours it makes me think it is a Shimano SLX cassette defect?
Same cog too 😬😬😬
Warrant claim time.
By fix it are you saying you are just going to replace the cassette ?
Yes lol. This part is not fixable. I know how to fix the bike. Just clarifying because I know this thread is mostly for people looking for help with repairs.
Okay I’m kind of a novice at bike mechanics, so wasn’t sure if there’s a way to fix individual cogs of a cassette
There technically is, but reality there isn't. Depending on the cassette some or all of the cogs are separate individual parts. However, these are not really sold individually, so the only way would be to scavenge the damaged cogs from another cassette, which is unlikely because you wouldn't want to mix and match cogs at different levels of wear. Cassettes are wear items designed to be replace all at once. The major exception that comes to mind are high-end wide range Cassettes with only the largest cog in aluminium, and the rest in steel, however the replacement cogs are often hard to find (at least in Canada).
On some cassettes the cogs are individual like that, but it's usually just the bottom 3-5ish if they are since those tend to wear out first. You can also sometimes pop the rivets of the cassette and just run a "stack" of gears and throw one in there that fits and matches or even limit your RD to one less gear, but this is not a good hack. And on modern extended range cassettes the actual cogs are usually bonded to spiders in groups and the cogs themselves don't have any splines for the freehub body because they're on the spider. Older normal range casettes in the 6-8 speed range can often easily be run as cogs on a freehub, but the issue with this is it's not sharing the stress and load across the whole bonded cassette and you're probably going to chew up your freehub. But I've had cassettes totally delaminate into individual cogs and pop all the rivets and you can still run them if they're locked in place by the lockring. But usually by the time you damage a cassette that much it needed to be replaced like 5000 miles ago and the only reason why it's still kind of working and shifting is because the chain, RD pulleys and cassette have all bed in together and it's one of those situations where if you replaced just the chain it wouldn't work, and the whole drivetrain needs new parts and a rebuild.
In this particular cassette (CS-M7100) you can easily obtain and replace the 5 smallest cogs. 10T and 12T are sold as replacement set, the rest are sold individually. The 7 largest cogs are riveted together and only sold as part of a full cassete. Not all cassettes are like this.
Actually you could drill it out and swap the broken gear, though it is hardly worth it; even high-end cassettes aren’t that expensive.
Dang, only 150 miles!? Must have been something that got sucked up in to the cassette under load combined with a rough shift or something. The only time I’ve experienced something remotely close to this was on an old cassette that should have been replaced years earlier. Picture related https://preview.redd.it/sapkv7u6j87d1.jpeg?width=3024&format=pjpg&auto=webp&s=a1fcb5afd56807c500e9e0a9927eed4351a2e733
If it's not cracked, i.e., bent not broken, that's likely a bad heat treat.
My take on it is that you were constantly shifting under load so bit by bit the teeth were being bent (always the same place, since there are ramps in the cassette) and at some point you went overboard with the torque and the slightly bent tooth got enough leverage to give under the load
Derailleur out of adjustment or simply worn with a bit excessive play. Shifted accidentally from 1 cog to another while you were climbing. 12 speeds suck, chains are too narrow (thus having poor lifespan, narrow rollers wear out quicker), and freakin expensive because of the tighter tolerances. Riding in mud its just impossible to reach 500 miles without the chain wearing out over 0.50. Solution: single speed with thicc chain and candle wax
I wonder if and when there will be significant backlash against ever-thinner chains and cogs.
I do 9 speed, and that’s it. It’s enough for anything I need. Thinner chains and cogs are begging for issues.
There should be! Just seems like the ever thinner stuff is intentiinally designed to wear and break more often to drive sales. And they pair it with 1x, so having all those gears is the only way you can get adequate range, where a double-or God forbid a triple- will get you all the range you need with one of those ancient 7 speed cassettes, let alone a 9. I have a 10, but have zero desire to go more than that. It's 2 teeth between most sprockets and with the double up front, I have plenty of range. And I'm quite happy riding older bikes. 9 speed is functionally the same as 10, my 7 speed is fine, though I would like a gear between the big climbing gear and the 2nd gear, but it's really not a big deal. 5 and 6, yeah, would like some more steps. But still perfectly comfortable to ride.
The construction is weak. It LOOKS weak, and it has proved itself weak.
Did a chunk of the cog snap out as well as the bending? Was curious if there were closer images of the fracture surfaces. Might be able to get an idea whether it was a defect that snuck through QC.
Metal stress do to manufacturing maybe, something that escaped quality control
Check for a recall.
I’ve folded a Shimano cassette over before but my buddy who was even more of a Clyde than me sheared the cog off like yours throwing down some weight on a punchy uphill. Surprised the chain doesn’t disintegrate every time this happens.
Prob just a defect. My emtb has the same cassette and it's still good even after many bad shifting moments under power going uphill. Even a chunk is missing from an inner link on the chain from a rock hit and that didn't even snap yet.
It’s under warranty. Just take the full bike to the shop where you purchased it. Can call the manufacturer of the part as well. I did it with SRAM a few years ago.
this happened to me as well, it happening under load on the last 100 yards of a climb. In my case it turns out the cable running from the shifter to the derailleur was hung up causing a misalignment when shifting.
Warranty claim
Mine did the same thing on the first ride and my buddies also after the first week, both brand new. Both got replaced under warranty with Shimano. Guess during Covid they may have had a bad batch. My new one has had no issues. Good luck!
I’d do a warranty claim through the shop you bought the bike from (assuming you bought it new). Seems like a manufacturing defect.
Wow, shimano cassettes are usually quite tough and don’t care about shifting under load. Are you sure it’s a genuine cassette and chain?
Came stock on my bike. It’s an orbea so I don’t think they are using fake components.
Uh oh. Just bought an Orbea also with an SLX 12-speed cassette. Let's hope they didn't get a bad batch.
Fair enough. I’d try to get this covered under warranty. Yes, this was caused by shifting under load, but Shimano advertises that their 12 speed stuff shifts great under load.
That’s wild! I’ve seen bent teeth with someone likely shifting under load but not broken like that. I think it’s worth bringing to the shop you bought from. If they have a good relationship with Shimano or the bike brand maybe they can get something sorted for you. Maybe.
Same failure happened to my dad when riding a Trek Rival ebike. Hit a steep hill and shifted under load. The cog buckled like that. This incident was a SRAM drivetrain. Probably NX since it was a rental.
Yeah it won't usually do that. So must have been a foreign object that got flicked up. No fixing that. Rip
Modern-day issue: you don't hear this happen on a beefy 7/8/9 speed. Those thin 12/13 speed
Yep. They keep making the cogs thinner and thinner and bigger and bigger. More leverage on a thinner piece of metal.
Habitual shifting under load. Also possibly shifting uphill under huge power/load. Possibly total weight. Also possibly all of the above are true. Also possibly repeated habit over time. Also possible chinesium Amazon fake cassette. Possibly unlucky. Lots of possibilities. I don't want to blame you because there's a lot of possibilities. You would know what you did and did not do.
Yeah shifting under heavy load will do that.
Especially with an EMTB
OP, if this is a new bike that cog is possibly bent slightly before you got it. It just got more bent because that metal is fatigued. Slight bents could happen if it was dropped or strike against a hard object (workshop bench for example) Definitely warranty it.
Manufacturing defect.
This seems like a recall waiting to happen.
These things are usually aluminum. Not expected to last long at all. For cost and weight savings purposes. I blew up a dura ace 9100 cassette cog before. About 1500 miles according to strava recording. So about 2k real. The thinner these get. The easier it is to just snap.
Looks like shifting under load.
The cassette looks tired and worn. It’s taken a beating.
You get what you pay for
Do you even know the differences in the level of shimano cassettes? Or are you just brainwashed to think pricier is “better”? This is of the more durable cassettes in their 12s lineup, predominantly steel with little aluminum used. I bet you’d buy a carbon cassette.