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  1. #1
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    Drivetrain problems in the granny gear.

    Hi,
    I have a 38t Action Tec cog. When I am in the granny gear upfront (18t) and the 38t cog in back, there is distinct noise and roughness when pedaling. In the middle ring (28t), the 38t cog works fine. I assume the cog goes on with the stamped Action Tec logo facing outward.

    I switched derailleurs thinking that would help. No luck. I replaced the 38t cog with a 41t cog, and still got roughness in the lowest combo. (18x41). The 38t cog worked fine for months without incident. Recently I took the wheels off, and now that I've remounted them I can't get the drivetrain to run smoothly in the 18x38 or 18x41 ratios. The b-tension screw is dialed in all the way and there appears to be enough clearance in between the last cog and the top derailleur pulley.

    I am stumped. Any help would be much appreciated. Thanks.

  2. #2
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    I'm sure no one wants to touch this - 18 X 38 and 42?
    Can you replicate the issue if you spin it up on a repair stand?
    The usual things to check would be chainline, stiff link or damaged chain, bent tooth front or back, damaged jockey wheel.

  3. #3
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    I checked for a bent tooth, checked the chainline, replaced the derailleur and the upper pulley, no stiff links. Not sure what the problem is.

    The rear cassette is either 12-14-17-20-24-30-34-38 or
    11-14-17-21-26-32-36-41.

    The bike works fine in the 18x36 combo which is adequate for most of my riding but it'd be nice to get the last cog to work properly.

  4. #4
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    Huh? Do you have a massive 1x11 cassette on there or something? 38 and 41 are pretty freaking low gears for the rear. As much as an 18 tooth Chainring is pretty small for the front.
    As far as orientation of the cogs themselves.........the side with small ramps should face outward.

  5. #5
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    Did you READ my post or not ? If so you'd realize that the bike is set up with an 8 speed drivetrain and that the 38 and 41t cogs are the last gears in SEPERATE cassettes. That's kinda why I specified tooth counts on two different cog stacks.

    Of course the ramps face outward on standard cassette cogs but the Action Tec titanium cog has no shift ramps of any sort which is why it's hard to determine which direction it goes in.

    Don't mean to come off as rude but it grates on me when people ask questions that make it obvious that reading comprehension is a lost art.

    The wheel size is 27.5", so lower ratios are needed than for 26" wheels, imo. If I need a higher gear than 18x38, that's what I have a rear derailleur and multiple gears for.

    Having checked everything else, it must be that the derailleur hanger is bent. I'll need to take it to an lbs to get it straightened out.

  6. #6
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    The only thing I can think of is the chain is rubbing on itself at the derailler pulley due to the excessive chain take up. This could be solved by removing 2 links make sure you still have enough chain to clear the two biggest cogs. Or it might be just a worn chain that only manifests because of the high torque of the small chainring. If you are going tinker with these setups keep short links of chain handy and join them with reusable links.
    "Dish is illogical." Spoke of Vulcan.

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