Problems with SRAM cassette on Shimano 8 speed
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  1. #1
    orlin03
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    Problems with SRAM cassette on Shimano 8 speed

    I recently gave my commuter bike some much needed love with new pads, new cassette, and a new chain. It has a Shimano Sora 8-speed group on it, and has always worked fine, especially considering it's a triple. To save money (you know, for the FUN bikes), I went with budget parts: a SRAM PG 820 cassette (11,12,14,16,18,21,24,28) and a SRAM 870 chain. Installation went smooth, and I thought I was good until I took it out and had problems holding certain gears.

    I checked the high and low limits with the cable off it's stop, and both appeared to be right on; with the cable attached, the chain lands perfectly on the 11 and the 28. Cable adjustment is very touchy, with a quarter turn too much either way from ideal making it not want to hold any gears when shifting in that direction (it was not this touchy before with the Shimano components, where "just a bit off" meant slower shifts in one direction). The problem is that, when shifting from the smaller cogs to bigger ones, it doesn't want to stay in one of the gears (usually the 21), and when shifting from bigger to smaller cogs, it acts the same way in either the 14 or 16 tooth cog. If I shift pass the cog and back to it, it is fine.

    Has anyone had trouble with this combination? Is this what I get for getting a cheap cassette? Is there anything I am missing?

  2. #2
    Rub it............
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    There should be zero issue running a Sram cassette and chain with Sora components. As a matter of fact, some manufacturers pair up these parts the same way on new bikes. So its not a compatibility issue.

    Depending on the condition of the bike, since its a commuter, I'd start by checking the rear derailleur hanger alignment and condition of the cables and housings. If there is any type of dirt/grime/corrosion inside the cables, which is my guess because of the "touchiness" of the barrel adjustments being made, then in can affect how it shifts.

    I probably would not be a bad idea to just go ahead and change cables since your giving it "some much needed love."
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  3. #3
    RoadBikeReview Member
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    I had good luck with that exact cassette and a much older Shimano 8sp system. It took a ride or two to get the cable tension dialed. Prior to that, I had symptoms similar to yours. Of course, now all those parts are posted for sale, as I soon shelled out the ancient levers. Be careful, a cable swap started the chain of events that has led me to 10 speed! Back on topic, if cable tension doesn't do it, fresh cables may be in order. It ain't the cassette.

    Paul

  4. #4
    RoadBikeReview Member
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    Is the chain the same length and the cassette the same cogs as the ones they replaced?

  5. #5
    orlin03
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    Thanks. The previous cassette was a 12-25. I didn't need the extra gearing and would love to have tightened it up, but the price called me in. The chain was set using the big/big method (53-27); this probably isn't ideal for the little/little combo, but 90% of my riding is in the city with the 39 ring.
    I was doubting the casstte quality because it just feels notchy, like when you put a newer cassette with a used chain. It has a black finish instead of chrome, so that might have something to do with the feeling.

    I was also thinking about replacing the cables, as well as dissassembling the RD, but what made me worry was that the cable and RD both worked fine before I put this on. It seems that is going to be my next step.

  6. #6
    RoadBikeReview Member
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    Quote Originally Posted by orlin03
    Thanks. The previous cassette was a 12-25. I didn't need the extra gearing and would love to have tightened it up, but the price called me in. The chain was set using the big/big method (53-27); this probably isn't ideal for the little/little combo, but 90% of my riding is in the city with the 39 ring.
    I was doubting the casstte quality because it just feels notchy, like when you put a newer cassette with a used chain. It has a black finish instead of chrome, so that might have something to do with the feeling.

    I was also thinking about replacing the cables, as well as dissassembling the RD, but what made me worry was that the cable and RD both worked fine before I put this on. It seems that is going to be my next step.
    A possible source of the problem is that your chain might be too short. Big/big and long cage derailleurs make the chain shorter than the recommended Shimano method, which rotates the rear pulley further away from cassette. Something to check, anyway. Shimano's technical site has directions for all of their rear derailleurs to set chain length.

    Also, make sure you cassette is on tight. Some cassette hub combinations require a spacer ring. Just make sure the cassette has no lateral float or play and none of the cogs have any wiggle.

    Try just lubing the moving parts on the RD with a penetrating oil, and grease the cables without unbolting them (if you have the usual slotted cable stops).


    I think if it isn't the chain length, what you're experiencing is a gummy, poor shifting derailleur system that was masked by a very compliant and easy shifting worn chain. The combination of new part and old is just making some of the wear more obvious. My best guess.

  7. #7
    orlin03
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    Quote Originally Posted by rx-79g
    Try just lubing the moving parts on the RD with a penetrating oil, and grease the cables without unbolting them (if you have the usual slotted cable stops).

    I think if it isn't the chain length, what you're experiencing is a gummy, poor shifting derailleur system that was masked by a very compliant and easy shifting worn chain. The combination of new part and old is just making some of the wear more obvious. My best guess.
    ^^Spot on! I knew it could use a good cleaning, and often blame grime for crummy shifts, but since it shifted good with that old chain I didn't think the crud was the problem. Great explaination! I lubed the whole cable, and removed the pulleys to clean them. One of the dust seals was bent on the upper pulley and there was grease left; all the parts have been scrubbed and lubed (I'll be replacing either the pulley & seals or the whole RD sometime in the near future). Shifts great and precise now! I am a bit ashamed that I didn't do this in the first place, especially since I'm such a stickler for cleaning my other two bikes.

  8. #8
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    Quote Originally Posted by orlin03
    ^^Spot on! I knew it could use a good cleaning, and often blame grime for crummy shifts, but since it shifted good with that old chain I didn't think the crud was the problem. Great explaination! I lubed the whole cable, and removed the pulleys to clean them. One of the dust seals was bent on the upper pulley and there was grease left; all the parts have been scrubbed and lubed (I'll be replacing either the pulley & seals or the whole RD sometime in the near future). Shifts great and precise now! I am a bit ashamed that I didn't do this in the first place, especially since I'm such a stickler for cleaning my other two bikes.
    So much for my guess...

    I was going to guess that you threaded the chain and missed the little tab on the derailleur cage, and went around it the wrong way. The results are exactly what you described.
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  9. #9
    orlin03
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    Quote Originally Posted by PlatyPius
    So much for my guess...

    I was going to guess that you threaded the chain and missed the little tab on the derailleur cage, and went around it the wrong way. The results are exactly what you described.
    Ooh... that takes me WAY back to my very first chain replacement. It's engrained in my thoughts now everytime I go to replace a chain; having to go all the way back to the shop for a new connector was not fun (I didn't keep spares or use Wippermans back then).

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