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Thread: Catastrophe?

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    Old, but not really wise CptjohnC's Avatar
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    Catastrophe?

    Last week, I was all excited about my new chain and cassette. The cassette in particular seemed so much better than my old one because of the shorter reach to the highest (largest) cog, as I went from a 34 to a 30.

    I rode several times last week, and all seemed well. This weekend, I went for a fun ride, and about 15 minutes in, as I slowed in preparation for a stop, my wheel suddenly locked up, and I nearly went a$s over teakettle. I knew I had dropped the chain, which I thought was weird enough, but then I looked down and saw this:







    So the chain is down between the cassette and the hub, having jumped 'over' the highest cog. I can't get the chain out with 'ordinary' force, and I don't want to make anything worse. My LBS installed the chain and the cassette, so I'm inclined to take it back to them and see what they can/will do.

    How likely is it that I'll need a new wheel? Is the cassette toast? How about the chain? Is my loyalty to my LBS misplaced? Was this caused by something they did or should have done (or not done)? I don't ~think~ there was rider error involved, as I was shifting pretty gently, and not pedaling all that hard.

    Thanks.

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    Senior Member Homebrew01's Avatar
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    The low limit screw was incorrectly adjusted. Chain can probably be pulled out without damage. You do not need a new wheel or cassette. Spokes will have to be examined to see if any need replacing (no big deal). If you're lucky, then just some small scratches.

    Bring it to the shop. I would expect them to fix at no charge if they were responsible for set-up and adjustment.
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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by CptjohnC View Post
    Last week, I was all excited about my new chain and cassette. The cassette in particular seemed so much better than my old one because of the shorter reach to the highest (largest) cog, as I went from a 34 to a 30.

    I rode several times last week, and all seemed well. This weekend, I went for a fun ride, and about 15 minutes in, as I slowed in preparation for a stop, my wheel suddenly locked up, and I nearly went a$s over teakettle. I knew I had dropped the chain, which I thought was weird enough, but then I looked down and saw this:


    So the chain is down between the cassette and the hub, having jumped 'over' the highest cog. I can't get the chain out with 'ordinary' force, and I don't want to make anything worse. My LBS installed the chain and the cassette, so I'm inclined to take it back to them and see what they can/will do.

    How likely is it that I'll need a new wheel? Is the cassette toast? How about the chain? Is my loyalty to my LBS misplaced? Was this caused by something they did or should have done (or not done)? I don't ~think~ there was rider error involved, as I was shifting pretty gently, and not pedaling all that hard.

    Thanks.
    First, this is a limit screw problem. That's one of the few times that I've ever typed that phrase without the 'not' between 'is' and 'a'. It may be because the shop messed with the limits during the install (not likely) or it may be that the screws have been misadjusted for a while and you just happened to have a bad day.

    The good news is that it won't hurt the cassette nor the chain. It may have damaged spokes but that usually depends on how hard you were pedaling when it happened and if you kept trying to pedal. In the first picture, it looks a little like you've got a damaged spoke but that may be a trick of the photo. Grab hold of the chain and try to pull it out. Then inspect the wheel for gouges on the spokes. You can even remove the cassette if you have the tools and inspect more closely. If the damage to the spokes isn't too bad, you can probably ignore it since where the damage occurred isn't in a high stress area. If you've gouged out a significant amount of spoke material (roughly 1/4 or more of the diameter) replace those spokes.
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    Take it back to the shop as is. They can remove the cassette to fish the chain out if it doesn't come out otherwise. I'd certainly assume they'd check derailleur adjustment when replacing a cassette. If that isn't a part of their repair, I'd quit going there. They should also replace any damaged spokes.

    As much as I hate them, what happened to the spoke protector? If it had one originally, did they not re-install it when they replaced the cassette? Bad on them unless they got specific instructions from you to NOT put it back on.

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    Old, but not really wise CptjohnC's Avatar
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    Quote Originally Posted by reddog3 View Post
    As much as I hate them, what happened to the spoke protector? If it had one originally, did they not re-install it when they replaced the cassette? Bad on them unless they got specific instructions from you to NOT put it back on.
    I was thinking about that, mostly in the "for want of a $2 piece of plastic, this?" kind of way. I do not believe I had a spoke protector, because my old mega-range 11-34 cassette probably didn't warrant it -- I'm not sure it would have been physically possible for the chain to jump off the high side.

    I definitely did not specify to leave it off or remove it. But I did specify replacing the old mega-range cassette with an 11-30 or 11-32 cassette, and I didn't consider whether a spoke protector would be necessary. Of course, I also figure they're the experts and they'd tell me if a part were needed.

    I know the shop has had some substantial turnover of mechanics the past few months, which is not comforting -- the old head mechanic was always good to me, took the time needed, etc... The last head mechanic seemed a bit 'off' in his personal interactions, which would be okay if he were a great wrench, but I'm not sure whether he was that. I'm not even sure whether they have a 'head' mechanic now. The owners are great guys, and fair wrenches in their own right (well, one is pretty good... the other is so-so, but he's a great bike guy in other ways, and he knows what he shouldn't mess with, generally). Unfortunately they've been less present at the shop lately.

    I'd hate to have to find a new shop, but I'm getting worried.
    Last edited by CptjohnC; 12-05-11 at 02:14 PM.

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    It is also possible that the derailleur hanger got bent slightly inward at some point after the new chain and cassette were installed, rendering useless the derailleur limit setting.

    Also, unless the new cassette was installed with a spacer, it should not have needed to have the limit switch altered... it should work just fine as it was.

    Although, if I were the mech in the shop, I like to think that I would have checked the derailleur settings after installing a new cassette.

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    Putting a chain and cassette on is literally a job for a monkey. It takes 5 minutes and is a simple checklist. When you change any cassette, you:

    a) Reset the high limit screw
    b) Reset the low limit screw
    c) Reset the cable tension
    d) Check the b limit screw

    That takes probably 1-2 minutes.

    If it was me, I'd be going back to the shop screaming for completely failing on such a simple task. FAIL. After they fixed it, I'd select a new LBS.

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    Quote Originally Posted by sideshow_bob View Post
    Putting a chain and cassette on is literally a job for a monkey. It takes 5 minutes and is a simple checklist. When you change any cassette, you:

    a) Reset the high limit screw
    b) Reset the low limit screw
    c) Reset the cable tension
    d) Check the b limit screw

    That takes probably 1-2 minutes.

    If it was me, I'd be going back to the shop screaming for completely failing on such a simple task. FAIL. After they fixed it, I'd select a new LBS.
    sorry rd adjustment costs money

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    Quote Originally Posted by DCB0 View Post
    It is also possible that the derailleur hanger got bent slightly inward at some point after the new chain and cassette were installed, rendering useless the derailleur limit setting.
    Ya buddy! I went over the bars on saturday and the bike took some hard hits. I was concerned I maybe bent the RD out of shape, but a quick glance said otherwise. In the confusion of the flip I did not notice my wheel had moved (old bike w/horizontal dropouts) and within ten minutes I had the same problem. Luckily I was able to wrench it out with my hands and not have to walk home. But I have seen them stuck hard enough that the cassette/freewheel needs to be removed to get the chain unstuck.

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    biked well well biked's Avatar
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    We check the limit screw adjustments any time we install a different rear wheel or install a cassette at our shop. Different parts don't always line up the same, as evidenced by the photo in post #1.

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    Quote Originally Posted by well biked View Post
    We check the limit screw adjustments any time we install a different rear wheel or install a cassette at our shop. Different parts don't always line up the same, as evidenced by the photo in post #1.
    +1 Even two "identical" cassettes by the same maker and with the same gear range may not line up with the rear derailleur exactly the same way. There are manufacturing tolerances with everything and you can't assume the limit screws set correctly for your current cassette will be good for its replacement. You have to check the adjustments for every change.

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    there's no debate that the low gear limit is (was) mis-adjusted. But assumption that it as this way all along, or done by the shop that replaced the cassette doesn't automatically follow.

    There's a third possibility, which in my experience is the most common cause of this sort of problem. Some time between when the cassette was replaced and the incident, the hanger might have been bent inward a bit, which takes all the adjustments, including LGL with it. In my experience limit screws are pretty reliable in keeping their settings, but bent hangers are very common, and this stuff happens.

    Of course, the hanger and limit error could have happened, and the shop replaced the cassette, but didn't figure the job included a free gear adjustment, so didn't check. Years (decades) ago, we routinely checked low limits every time we serviced a bike. It was a 10 second check done by manually pushing the RD in to see if it would over derail. It was good customer service, but we really did it as a sort of defensive medicine, knowing that we'd be blamed for any mishap that happened within a few days of a repair.

    In New York, it wasn't worth arguing that nothing we did fixing your front flat could have led to the Rd going into the spokes, so we always did a free LGL adjustment in self defense.
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    Quote Originally Posted by sideshow_bob View Post
    Putting a chain and cassette on is literally a job for a monkey. It takes 5 minutes and is a simple checklist. When you change any cassette, you:

    a) Reset the high limit screw
    b) Reset the low limit screw
    c) Reset the cable tension
    d) Check the b limit screw

    That takes probably 1-2 minutes.

    If it was me, I'd be going back to the shop screaming for completely failing on such a simple task. FAIL. After they fixed it, I'd select a new LBS.
    I'm sure you get great service at the LBS after you tell them they are doing the job of a monkey.

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    Quote Originally Posted by FBinNY View Post
    In New York, it wasn't worth arguing that nothing we did fixing your front flat could have led to the Rd going into the spokes, so we always did a free LGL adjustment in self defense.
    Sometimes you just can't win. I once adjusted a front derailleur on a kid's department store aluminum bike (early/mid nineties when the first aluminum dept. store bikes came out), and his dad came in three days later furious because the bottom braket had pulled out of the shell and taken all the threads with it.

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by sideshow_bob View Post
    Putting a chain and cassette on is literally a job for a monkey. It takes 5 minutes and is a simple checklist. When you change any cassette, you:

    a) Reset the high limit screw
    b) Reset the low limit screw
    c) Reset the cable tension
    d) Check the b limit screw

    That takes probably 1-2 minutes.

    If it was me, I'd be going back to the shop screaming for completely failing on such a simple task. FAIL. After they fixed it, I'd select a new LBS.
    Sorry but if I'm changing a cassette, I might check the high and low limit but I seldom have had to do anything to them. Modern cassette have such close tolerances that adjustments are almost never needed.
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    Quote Originally Posted by cyccommute View Post
    Sorry but if I'm changing a cassette, I might check the high and low limit but I seldom have had to do anything to them. Modern cassette have such close tolerances that adjustments are almost never needed.
    I agree... generally, most cassettes are flat on the back of the biggest cog and that is pressed up against the raised boss on the inside end of the cassette, so changing cassettes generally does not do anything to the end points.

    Another possible scenario (along with shop error during installtion and a bent derailleur hanger) is that either the endpoints were always mal-adjusted but never became a problem until the OP was inadvertantly trying to get from the 30T cog to an easier gear he expected to be there.

    Luckily, as mentioned above, there is likely not much permanent damage to the bike as a result.

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    I'm betting on the bent Der Hanger, and it might have happened before OR after the installation of the new cassette and chain. I will throw another idea out there, perhaps the wheel wasn't reinstalled correctly (not bottomed in the dropout). I've seen that happen too.

    I wrench part-time in a shop and maintain my own family fleet of bikes, and I can tell you that this isn't rocket science, but I can see it happen. I believe that EVERYONE needs to know the basics of what to watch for on their own bikes so this doesn't happen to them. Blaming the LBS doesn't mean crap if you're on a 50 mile ride and stuck in the boonies. Hell, I check my oil after having my car serviced by a shop - JIC ...
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    Quote Originally Posted by DCB0 View Post
    I'm sure you get great service at the LBS after you tell them they are doing the job of a monkey.
    Given it's the job of a monkey, I'm the only monkey who works on my bikes.

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    In terms of the discussion of the bent hanger; it is possible but pretty unlikely. The chain and cassette were replaced a week before this happened. I've ridden the bike 3 times before this ride -- 2 round trip commutes and one other 'fun' ride, a total of less than 50 miles. No falls, no hits that I'm aware of. The bike lives in my office during the day, and in my house at night. It did ride on a car bike rack a few times, but neither of my racks put anything anywhere near the RD. So is it possible? Sure. Likely? no.

    I will note that the new cassette is a different brand -- SRAM instead of Shimano. While I don't think this makes a huge difference (both 8 speeds) perhaps it might be enough, coupled with the significant change in the upper cog size?

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    Quote Originally Posted by CptjohnC View Post
    In terms of the discussion of the bent hanger; it is possible but pretty unlikely. The chain and cassette were replaced a week before this happened. I've ridden the bike 3 times before this ride -- 2 round trip commutes and one other 'fun' ride, a total of less than 50 miles. No falls, no hits that I'm aware of. The bike lives in my office during the day, and in my house at night. It did ride on a car bike rack a few times, but neither of my racks put anything anywhere near the RD. So is it possible? Sure. Likely? no.

    I will note that the new cassette is a different brand -- SRAM instead of Shimano. While I don't think this makes a huge difference (both 8 speeds) perhaps it might be enough, coupled with the significant change in the upper cog size?
    The size is not an issue. The limit screws stop the lateral movement of the derailleur independently of cog size. If the derailleur was capable of pushing the chain off the cog with a 30, it would have been able to push the chain off the cogs on a 34 provided the spacing was the same.

    If the bike was handled with kid gloves as you say then it is most likely an adjustment issue.

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    biked well well biked's Avatar
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    Quote Originally Posted by CptjohnC View Post
    I will note that the new cassette is a different brand -- SRAM instead of Shimano. While I don't think this makes a huge difference (both 8 speeds) perhaps it might be enough........
    It most definitely could be enough to cause the problem you had, the two cassettes will not be absolutely identical for sure. If I were going to guess, I'd guess the new, slightly different cassette was installed, the low limit adjustment was not checked afterwards, and with the slightly different cassette installed, with a hard shift to the lowest gear, the chain went beyond the largest cog and into the spokes. It could have been caused by something after the installation, but my first guess would be an improper low limit setting since it was such a recent change of the cassette.

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    >The good news is that it won't hurt the cassette nor the chain.

    Meh, happened to me and it bent a link in the chain. "It" being my unsubtle attempts at unsticking it...

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    Quote Originally Posted by CptjohnC View Post
    I will note that the new cassette is a different brand -- SRAM instead of Shimano. While I don't think this makes a huge difference (both 8 speeds) perhaps it might be enough, coupled with the significant change in the upper cog size?
    Probably not. Again, the tolerances on cassettes are so tight that a variation large enough to cause an over shift is highly unlikely. This is one of those occurrences that happens. You aren't likely to be able to duplicate it nor find an easy explanation. All of the issues suggested are possible with some being more likely than others. Perhaps there's some smutz behind the cassette that doesn't let it sit quite flat (unlikely), maybe the new chain has a tight(ish) link (possible), maybe your mechanic did what sideshow_bob suggested and readjusted everything (possible), maybe you pushed the lever a little harder than normal and the limit screw wasn't set quite right (possible), maybe the cassette body wobbled more than it should have (unlikely), etc. The list can go on and on.

    Pull the chain out, check the adjustments, and ride. No real harm...and it could have been a lot worse...no real foul.
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    Quote Originally Posted by cyccommute View Post
    Probably not. Again, the tolerances on cassettes are so tight that a variation large enough to cause an over shift is highly unlikely.
    We'll have to agree to disagree on that.

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    It worked well for several rides then jumped? I bet something happened between the cassette change and the stuck chain.
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