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  1. #1
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    XT CS-M760 Cassette bending

    I just bent the largest and next largest (1 & 2) on a 11-34 XT cassette. This one was new in January, replacing one that I bent 2 & 3 on. Both have a 5 arm carrier. I am using an XT chain and dérailleur. I realize that I am just a huge power machine , but why do these keep bending. Never had a problem in 19 years of MTBing.

  2. #2
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    Quote Originally Posted by crashtestdummy
    I just bent the largest and next largest (1 & 2) on a 11-34 XT cassette. This one was new in January, replacing one that I bent 2 & 3 on. Both have a 5 arm carrier. I am using an XT chain and dérailleur. I realize that I am just a huge power machine , but why do these keep bending. Never had a problem in 19 years of MTBing.
    On the new ones Shimano increased the number of support arms from 4 to 5. I would imagine this will stiffen things up and resist the bending issue. Because the 34 is such a big cog and it's only being supported by those 4 arms its prone to bending I guess.

  3. #3
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    Quote Originally Posted by Tinshield
    On the new ones Shimano increased the number of support arms from 4 to 5. I would imagine this will stiffen things up and resist the bending issue. Because the 34 is such a big cog and it's only being supported by those 4 arms its prone to bending I guess.
    Except that as noted in the 3rd sentence, both of my bent cassettes have 5 arms, not 4.

    I am going to call Shimano about this problem.
    Their web site says "Shimano warrants to the original retail purchaser that the Shimano bicycle division product for which they received this warranty, is free from non-conformities in material and workmanship for a period of two years and their Dura-Ace and Shimano XTR components/wheels are covered for a period of three years from the date of original retail purchase. Shimano shoe products, soft goods and other wheels are warranted for a period of one year."

    http://bike.shimano.com/publish/cont.../warranty.html

  4. #4
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    I bent a 4 arm XT 11-34 and now my LBS has called to say I bent a SRAM 990 11-34 as well.

    I don't cross-chain and am running a 2x9 setup.

    This is getting pricey.

    I'm trying an 11-32 LX next because I have a spare one lying around.
    Mike
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  5. #5
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    Quote Originally Posted by MS MSP
    I bent a 4 arm XT 11-34 and now my LBS has called to say I bent a SRAM 990 11-34 as well.
    I don't cross-chain and am running a 2x9 setup.
    This is getting pricey.
    I'm trying an 11-32 LX next because I have a spare one lying around.
    I would sure like to understand my problem. I don't cross chain either, and I ride seated, so nothing extreme being done to the drivetrain (I've broke 1 chain in 19 yrs of mountain biking).

    I've bent chainrings before, but from rock hits. Both of my cassettes are bent away from the spokes, hard to do with rocks or crashes.

  6. #6
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    Everytime I have seen this, it is usually the XTR cassette and it's the Ti cogs that get bent because of shifting with torque applied. This is NOT crosschaining, but chain goes up the ramps, hits a few teeth but doesn't make get to complete wrapping the cog due to the lateral force from full crank torque still going. Usually, the chain will just skip and hop on the LX cassette which is chrome plated and relatively slippery. The XT & XTR, however, have a nice surface for the chain plates to grab on and ramp up. Also, many riders will keep trying to shift by holding the shifter engaged and forcing the issue.

    This is where the rapid-rise derailleurs can help, because they will usually just skip and hop along the ramps until the linear pull of the chain drops and the spring force of the derailleur can complete the shift. The best practice, of course, is to shift with little chain load. It just doesn't seem like the load is that hight at the time, but it is usually what bends cogs and prematurely ruins cassettes.
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  7. #7
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    I bent the 30 tooth cog outward too on my last XT cassette (11-34, 5 arm carrier). Fixed with a hard surface, a hammer and a punch. Did the trick for a temp fix.

  8. #8
    bang
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    this isn't an uncommon issue with the xt cassettes; just sift through the reviews. lx would last awhile though (i've had mine for 2.5 years with no issues), but it comes with a big weight penalty.

  9. #9
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    I completely bent the second biggest cog last fall on a newer 4 arm XT and had to throw it away. Yesterday while riding on some pretty steep stuff I bent the third and fourth biggest rings slighly. It was enough so that the chain would start skipping around. I fixed it with a screw driver but I am going to replace it with a SRAM 970. Interesting, the cheaper and heavier cassettes might not bend as easy.

  10. #10
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    I sent my bent cassettes into Shimano, and today there was a pair of them waiting for me on my front porch. Shimano stands behind their product.

  11. #11
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    I broke one earlier in the year

    Less than a month old, shifted up one cog and "Snap", the large cog cracked right through a "lightening" hole and bent over into the second and third cog, back to SRAM for me.

  12. #12
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    Learn to shift properly, not while under high loads.

  13. #13
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    Quote Originally Posted by smithy
    Learn to shift properly, not while under high loads.
    I think that's the ticket!

    I bent one of the rings on my XT cassette pretty bad, due to getting something stuck in my chain, about 3 years ago. I used a pin, hammer, and flat surface to fix it and am still riding that cassette to this day.

    Not passing judgment on anyone but if you're bending cassette's regularly without getting something stuck in the chain/derailleur/cassette then you need to take a look when/how you're shifting.

  14. #14
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    I gave up on the XT 11-34...bent two of them, each time the 2nd largest cog. Bent one of them back and rode it for awhile, but then it got bent again. Bad design or mfg. defect I say.

    Been riding with XTR since and no problem except the hefty price.

  15. #15
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    Quote Originally Posted by smithy
    Learn to shift properly, not while under high loads.


    I have been shifting bike gears since the early 70's. MTBing since 88. Besides 2 broken chains and some rock bent chainrings, these have been the first drive train components that I have had a problem with. So don't be so quick to judge without knowing the facts.
    Shimano warrantied both cassettes, so perhaps they think there was a problem with the part.

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