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  1. #1
    Lets Ride Trekke's Avatar
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    Middle Chain Ring Problems

    Just got my bike back from the LBS. New chain and new cassette. Everything shifts great except the chain jumps off the middle chain ring when I put a lot of pressure on it like out of the saddle up a hill. Does not happen in the big or small chain ring.

    The chain rings have 5,800 miles on them with the middle having probably 75% or more. I hardly ever use the small.
    The front DR is not touching or pushing against the chain and this happens no matter what rear cog I am on.

    My guess is the chain ring is worn and doesn't match the chain. Any other possibilities?

    OBTW - Campy Veloce 10 speed. Rear cassette is original replacement 12 x 23 and chain is original Campy record Chain 10s
    Phil

  2. #2
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    Middle ring is most likely the culprit. Other possibilties, did they do anything with the b.b.? If they replaced it with a b.b. with a longer spindle it could have an adverse effect. My money is on the middle ring though.

  3. #3
    Lets Ride Trekke's Avatar
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    No work on the BB unless a tune up requires the tech to take a look but they were repacked back in the fall.
    Phil

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    It soundds like the chainring has a lot of miles on it and should be replaced regardless of whether or not it's the culprit. Try that first, if you still have a problem then you have eliminated one possibilty and can move on with your diagnoses.

  5. #5
    Lets Ride Trekke's Avatar
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    Good advise. I am swinging the bike by the shop tomorrow. I had a warranty issue that required a part replacement from Bontreger so I will replace the CR at that point.

    I have had Shimano CR's and they lasted several years with me only changing the chain and cassette annually. The metal seems really soft on these rings. Maybe just my immagination.

    Thanks.
    Phil

  6. #6
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    5800 miles is not many for a chainring, I would expect more like 15,000 to 20,000 miles, but what you;ve described does sound like a wornout chainring. How about the chain, have you measured it?

    Al

  7. #7
    Klaatu barada nikto cascade168's Avatar
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    Quote Originally Posted by Trekke
    My guess is the chain ring is worn and doesn't match the chain. Any other possibilities?
    Have you tried adjusting the cable tension? Assuming that all of your other derailleur adjustments are correct, the last thing to finish an FD adjustment on a triple is to tweak the cable tension so the middle ring takes the shift properly. Just because it shifts smoothly on a stand does not mean that it will perform smoothly under load. Try turning the barrel adjuster on the FD cable (I'm assuming you have one). Just try a half turn at a time and see what happens. If there is no effect go back and turn in the other direction. More often than not, if your chain is slipping off the ring, then you do not have enough tension. To increase the tension you need to turn the barrel adjuster counter clockwise (like you are unscrewing it - this, in effect, lengthens the cable housing and increases the tension). This could easily fix your problem. The main reason the cable adjuster is there is for the middle ring. With a double chainring you really don't even need a cable adjuster. Cable tension does not have a lot of effect on the shifts to the large and small chainrings. They are affected (mostly) by the initial position of the cable (i.e. make sure it is pulled tight before you lock it down) and the limit screws. The road test often shows that the job is not finished.
    "Work is the curse of the drinking class."
    - Oscar Wilde

  8. #8
    Lets Ride Trekke's Avatar
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    Update: I took the bike back to the shop and they looked at the issue. MCR was worn badly. Trek was already replacing the Bontrager crank and luckly the replacement included the chain rings as well. 15 minutes later bike is perfect again.

    One thing I have to say is that Trek Warranty Service has been absolutly great since I bought my first bike over 6 yrs ago. Despite their questionable business practices and wholesale name (everybody has one) the experience with warranty or service issue has been top. I give a lot of credit to the LBS also. I have a Trek, two Gary Fishers and a Lemond.

    Anyway test rode the bike a little while ago and all is well.
    Phil

  9. #9
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by Trekke
    Just got my bike back from the LBS. New chain and new cassette. Everything shifts great except the chain jumps off the middle chain ring when I put a lot of pressure on it like out of the saddle up a hill. Does not happen in the big or small chain ring.

    The chain rings have 5,800 miles on them with the middle having probably 75% or more. I hardly ever use the small.
    The front DR is not touching or pushing against the chain and this happens no matter what rear cog I am on.

    My guess is the chain ring is worn and doesn't match the chain. Any other possibilities?

    OBTW - Campy Veloce 10 speed. Rear cassette is original replacement 12 x 23 and chain is original Campy record Chain 10s
    5,800 miles isn't very much wear for a chainring, but I suspect that you might be right. The tip off is that you have recently replaced the cassette and chain. If the teeth on your chainring look pointy or if you can lift the chain off of your middle ring with a lot of slack, it's time.

  10. #10
    Lets Ride Trekke's Avatar
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    Quote Originally Posted by Retro Grouch
    5,800 miles isn't very much wear for a chainring, but I suspect that you might be right. The tip off is that you have recently replaced the cassette and chain. If the teeth on your chainring look pointy or if you can lift the chain off of your middle ring with a lot of slack, it's time.
    I agree. 5800 miles is nothing. I keep the chain cleaned and lubed religiously. As I said in the original post the metal on the Cr's seems soft. Maybe the new one will be better. Bontrager doesn't actually make the component. TruVativ makes these for Bontrager. from what I have learned it seems there was a bad batch of these. We'll see.

    Thanks all for the feedback. Things are shifting perfectly now.
    Phil

  11. #11
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    Quote Originally Posted by Trekke
    Despite their questionable business practices and wholesale name (everybody has one)
    Anyway test rode the bike a little while ago and all is well.
    Glad you got the problem fixed. Sounds like you came out little bit ahead.

    This is off topic but since the OP brought it up I'm going to continue it. This is the first I have heard of Trek having "questionable business practices" and I'm curious to know what you might be refering to. I don't take offense to your statement it just makes me wonder. Is there anything that is documented or is it just rumor?

  12. #12
    Lets Ride Trekke's Avatar
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    Quote Originally Posted by Pete Hamer
    Glad you got the problem fixed. Sounds like you came out little bit ahead.

    This is off topic but since the OP brought it up I'm going to continue it. This is the first I have heard of Trek having "questionable business practices" and I'm curious to know what you might be refering to. I don't take offense to your statement it just makes me wonder. Is there anything that is documented or is it just rumor?
    Pete, I could probably search this forum (and others) and find thousands of post discussing Trek's business practices both good and bad. I won't try to defend or support either position. My personal experience with Trek has been excellent. Out of all the bike brands Trek gets bashed very openly and emotionally in public forums.
    Phil

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