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  1. #1
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    Problems with new SRAM chains (jumps under torque) *SOLVED*

    I recently needed to change my old SRAM PC-69 chain that has been flawless and shifts like butter to this day even though the chain has stretched 1/8" @ 12" mark.

    So I decided to buy a new PC-991 "CrossStep." I installed it to the same length as the old.

    PROBLEM:
    As soon as apply lots of torque (like on a power start or steep climb), the chain skips. It tries to jump to the next cog on the rear but never does. I've played with adjusting the RD (rear cable and alignment), tried fine tuning at the shifter knob. I've spent 30 solid minutes trying everything but I can't get this to work. I get close but it will still skip while under torque.

    So I put back my old chain and it shifts as sooth as silk.

    I decided to buy another PC-991 but without the "CrossStep".....I opened the packaging and see it's identical to the "CrossStep" but without the pins being pinned. It has the same outer width so it will give me the same problem.

    So here I sit with 2 brand new chains ($90) that will not work for me. It seems the new "bulge" type plates are causing issues with my RD/Cog. Look at picture below for comparison. You can clearly see the outer plates are wider on their new chains.

    FYI: The rear Cog is also a SRAM that is not worn. The RD is a good M960 XTR. New XT R/F shifters.

    Any ideas?

    ps. Anyone that wants to buy a brand new pc-991 chain let me know...I'll sell the spare cheap.
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    Last edited by RaveOn; 04-03-2009 at 06:29 PM. Reason: solved issue

  2. #2
    bike rider
    Reputation: Lelandjt's Avatar
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    Your stretched chain wore the teeth of your cassette so now any new chain will skip on it. Put your old chain back on and ride until the new cassette you are ordering comes in.
    Keep the Country country.

  3. #3
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    Quote Originally Posted by Lelandjt
    Your stretched chain wore the teeth of your cassette so now any new chain will skip on it. Put your old chain back on and ride until the new cassette you are ordering comes in.
    What he said. LOL

  4. #4
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    ditto you waited to long

  5. #5
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    I've dissected the cassette and there are no sharp edges and the openings are nice and rounded....not elongated like they get over time. I've removed the cassette, cleaned it and checked for wobbly gears...its all in good shape. If there is a problem with it, I can't visually see it.

    I don't mind buying a new cassette but I don't want to keep dumping money into a fruitless cause.

  6. #6
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    This may be a really dumb question...are you putting a 9-spd chain on an 8-spd cassette?
    I know the gaps in the pictures 'look' the same, but I just measured them with a piece of paper and pen on my monitor and it 'seems' like the 991 is slightly narrower than the 69. (FWIW I've never had a 9-spd., so I've never seen them side by side - and am probably talkin out my ass )

    sorry if I'm completely wrong - I'm just throwin some sh!t against the wall in the hopes that something will stick...If not , go with the above recommendations of a new cassette
    Honestly... ahh I give up

  7. #7
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    If you had an 1/8" of chain stretch at 12" I think your cassette is toasted. Even if all the gears look smooth and are not bent, the old worn out chain deformed the cassette......and no matter how many new chains you buy, it will never work until you get new rear cogs.
    How many miles/years did you have the old chain on for? Being that it is a PC69, it must have been a long time.

  8. #8
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    Yup. Toasted cassete.

    Every time this happens to me I vow to change my chain more often. Sometmes I even listen to my own advice.

    Sometimes.

  9. #9
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    I used to distribute SRAM chains, and made no friends at the company when I told them that they were making a mistake moving from the flat outer plates to the bulged ones. I still prefer the flat plate design, which I think is smoother running.

    In your case, however, I suspect that the problem is more likely the result of running your old chain too long, and wearing the smaller cogs beyond where they'll run with a new chain. Given that the harm is already done, do what I do, and keep running both the old chain and cassette until they are absolutely, positively toast. You'll be surprised at how much "free" life you can milk out of them.

    Save the new chains for when you replace the cassette.

    BTW- I have a few new PC-59's left (same vintage as your old stuff), though they're from a bulk carton and aren't individually boxed. PM me if you're interested.
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  10. #10
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    You know, at this point I don't want to risk wearing out my new BB30 crankset. I just ordered a new PG-990 cassette. Jenson has a sweet sale....$65.

  11. #11
    ~Disc~Golf~
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    there ya go bud - nice call!
    Honestly... ahh I give up

  12. #12
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    Quote Originally Posted by FBinNY
    I used to distribute SRAM chains, and made no friends at the company when I told them that they were making a mistake moving from the flat outer plates to the bulged ones. I still prefer the flat plate design, which I think is smoother running.
    Yeah, the new "bulged" outer plates leave little if no room for error. When I lay the PC-991 chain on my (old) cassette, the chain gets moved slightly to the outside. It moves slightly outside because the bulge pushes it there. I was actually surprised to see that. Now I wonder how sensitive it will be if I get some small debris caught in there. In the past it would chew it up but now I wonder with the tolerance so small, it may skip with this new design. I think companies (like sram) are forced each year to come up with "new designs" to improve profit margins. A good example of this is the new 10spd setup. WTF. Some things die from improvement!

    I also wonder if spacing gap between the teeth is slightly smaller in my Sram 9.0 cassette when compared to the new PG-990 cassette....further compounding my problem.

    I'll update this post after I put new cassette in.

    Thanks for the help guys I think deep down I knew what I needed to do but sometimes you need someone to push you over that edge

  13. #13
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    Quote Originally Posted by Lelandjt
    Your stretched chain wore the teeth of your cassette so now any new chain will skip on it. Put your old chain back on and ride until the new cassette you are ordering comes in.
    haha, real subtle marketing technique there
    Don't take life too seriously, you'll never get out alive.

  14. #14
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    Quote Originally Posted by RaveOn
    Yeah, the new "bulged" outer plates leave little if no room for error. When I lay the PC-991 chain on my (old) cassette, the chain gets moved slightly to the outside. It moves slightly outside because the bulge pushes it there. I was actually surprised to see that. Now I wonder how sensitive it will be if I get some small debris caught in there. In the past it would chew it up but now I wonder with the tolerance so small, it may skip with this new design. I think companies (like sram) are forced each year to come up with "new designs" to improve profit margins. A good example of this is the new 10spd setup. WTF. Some things die from improvement!

    I also wonder if spacing gap between the teeth is slightly smaller in my Sram 9.0 cassette when compared to the new PG-990 cassette....further compounding my problem.

    I'll update this post after I put new cassette in.
    The on-center spacing of "new" Sram 9s cassettes is unchanged from the older ones. 9s is 9s, otherwise, they'd need to change the levers.
    While I'm not a fan of the buldge, you'll note that it doesn't go much farther (if at all) than the overall pin width and therefore shouldn't be noticeably more sensitive.

    Possibly, it might want a slight more outside bias on the trim, since the purpose of the buldge is to make the chain grab and climb the adjacent larger cog more agressively. You might also take the time to check hanger alignment. Often chains and cogs which are worn in together are more forgiving than new stuff and may mask another problem.

    There is a difference between climb-out under load from worn chains and cogs and ghost shifting which usually has different causes. If worn cogs aren't the problem, a new cassette won't magically cure it. Or you can use the backwards approach of the TV show "House". "If the treatment works, then the diagnosis must have be right".
    Last edited by FBinNY; 03-29-2009 at 12:41 PM.
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  15. #15
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    I figured it would only be fair to do a follow up.

    I just installed my new SRAM PG-990 cassette with the same (new) PC-991 chain and everything works perfect again

    Thanks again folk

  16. #16
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    So the offer for a "new PC- 991 cheap" is probably off the table?

  17. #17
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    Every time my chain wears out I just buy a new bike.

  18. #18
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    Quote Originally Posted by Justanuthabika
    So the offer for a "new PC- 991 cheap" is probably off the table?
    If you didn't notice, I actually bought another new PC-991 thinking "it can't possibly be my cassette that is worn." Bzzzzttt....wrong assumption

    So yes I have another new PC-991 I'd sell. The one I ended up using was the first one and since I mounted it I kept that one. The 2nd PC-991 I have I just bought, opened package and said its the same chain so I didn't mount it. So this is brand spankin' new. First one to paypal me $27 I'll ship it to you for free (within the US). Send me a private message if interested. My invoice for it was $34 (and that was at a nice discount).

    Quote Originally Posted by xmangox
    Every time my chain wears out I just buy a new bike.
    Dayum. If I had that kind of money I'd do that when I get a flat and donate my old flat-tired bike to folks with messed up cassettes.

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