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  1. #1
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    roadside repair for internal routed RD cable?

    I was out on a group ride last Sat and one of the riders in the group was having problems with their rear der. - at first it would only shift through the top 5-6 cogs, and gradually got worse/less cogs. Bike had internal cable routing so I couldn't really tell how tight or slack the der cable was at any particular time. Bike was reportedly only about a month old and the rider was a novice, FWIW.

    I tried shortening the cable (2" or so!), picked up another cog lower at first but the shifter felt like the cable was slipping somewhere, and it kept getting worse (fewer of the top gears. Definitely not a broken cable as the shifter would function, just not full range. Rider took it in to a shop after the ride, and was told that 'the cable was too tight and some spacer got lost inside the frame' which is kinda what I suspected might be going on.

    Does that explanation make sense, and is there any way to fix it on the side of the road if I ever encounter it again? Short of cutting the cable and tying it off with the tension putting the RD in a middle gear, of course. Didn't think about it at the time, but could we maybe have adjusted the limit screw to force the der into something other than the smallest cog - not sure if that screw would have enough travel to do that.

  2. #2
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    As you thought after the fact, using the high limit screw to pick another cog is what's done most of the time for a broken rear DR cable and sounds like it would have been a good quick fix in this case.
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  3. #3
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    I think you're too quick to assume it's not a broken (more specifically frayed) cable. Although if it's true the bike is only a month old that might be unlikely. Either way tell the guy to yank his cable out of the shifter and check the first few inches after that little knob thing.

  4. #4
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    From my mistakes, I would not have made a major change (cutting 2" off a shift cable) on a ride.

    Rider was getting 5 or 6 gears - good enough to finish the ride or bail and ride home. When you start messing with changes that you cannot undo in the field, you risk ending up in a worse place (e.g., one gear).

  5. #5
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    Quote Originally Posted by Srode View Post
    As you thought after the fact, using the high limit screw to pick another cog is what's done most of the time for a broken rear DR cable and sounds like it would have been a good quick fix in this case.
    How far over can you go this way - 2nd or 3 smallest cog, or more?

  6. #6
    tlg
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    Quote Originally Posted by sdjeff View Post
    How far over can you go this way - 2nd or 3 smallest cog, or more?
    The limit screw will get you 2 or 3 cogs.

    This trick is even better. You can get just about any cog you want. And pretty easily adjust to a different cog if you had a large hill to go over.



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  7. #7
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    Quote Originally Posted by crit_boy View Post
    From my mistakes, I would not have made a major change (cutting 2" off a shift cable) on a ride.

    Rider was getting 5 or 6 gears - good enough to finish the ride or bail and ride home. When you start messing with changes that you cannot undo in the field, you risk ending up in a worse place (e.g., one gear).
    Didn't cut the cable, just loosened the clamping bolt on the RD and pulled it through with the longer stub end sticking out past the clamping bolt so that at least would be reversible.

    But by the end of the ride, he did only have the top cog. Almost like the housing was gradually pulling through a stop, or the cable was slicing through a liner inside the frame reducing the effective housing length.

  8. #8
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    Quote Originally Posted by tlg View Post
    The limit screw will get you 2 or 3 cogs.

    This trick is even better. You can get just about any cog you want. And pretty easily adjust to a different cog if you had a large hill to go over.



    Wow! I knew about the high limit adjust screw method, but never saw this other method to get you to even larger cogs. This is great to know!
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  9. #9
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    Quote Originally Posted by sdjeff View Post
    I was out on a group ride last Sat and one of the riders in the group was having problems with their rear der. - at first it would only shift through the top 5-6 cogs, and gradually got worse/less cogs. Bike had internal cable routing so I couldn't really tell how tight or slack the der cable was at any particular time. Bike was reportedly only about a month old and the rider was a novice, FWIW.

    I tried shortening the cable (2" or so!), picked up another cog lower at first but the shifter felt like the cable was slipping somewhere, and it kept getting worse (fewer of the top gears. Definitely not a broken cable as the shifter would function, just not full range. Rider took it in to a shop after the ride, and was told that 'the cable was too tight and some spacer got lost inside the frame' which is kinda what I suspected might be going on.

    Does that explanation make sense, and is there any way to fix it on the side of the road if I ever encounter it again? Short of cutting the cable and tying it off with the tension putting the RD in a middle gear, of course. Didn't think about it at the time, but could we maybe have adjusted the limit screw to force the der into something other than the smallest cog - not sure if that screw would have enough travel to do that.

    Cables don't just get longer without a good reason. Contrary to popular belief, they don't stretch when new. They "stretch" when strands are starting to break. It is usually an early warning sign of a complete break. Latest generation Shimano STI shifters are known for chewing up cables inside the shifter. I just had one go south at 1500 miles. Poor, clunky shifting is the first warning sign. The next warning sign is being one cog smaller than where you should be. At this point, the best advice is taking a b-line home and changing the cable. If you can't get that far without doom, the Art's Cyclery video tlg posted is a great resource.
    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein

    "Beware of geeks bearing formulas."
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  10. #10
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    Quote Originally Posted by Lombard View Post
    Cables don't just get longer without a good reason. Contrary to popular belief, they don't stretch when new. They "stretch" when strands are starting to break.
    When new, cable housings need to get seated into stops with decent cable tension. If this is not done by the installer, the housings will shrink slightly (what some may call cable"stretch") as the tension is provided under typical use.

    One thing that also happens over time is the steel inner cable wears the softer plastic housing liner. As this happens over time, the path the inner cable takes get slightly shorter. The requires slight tension adjustment over time as the cable wears the liner.
    The shifter and derailleur system (pull ratios) can affect how sensitive the adjustment is to liner wear. The old Shimano 10 speed was was more sensitive than the new 11 speed system, as the shifter pull per shift increased 20% on 11 speed system (making it less sensitive) and so easier to set-up and maintain.

    Here's the problem for shifters that have under the bar tape housing exits - The steel inner cable wears the housing liner (and not the cable) everywhere along the length except for a few inches inside the shifter itself. This is before the liner and housing start.
    For the first few inches after the shifter cable stop, there is steel on steel contact between the inner cable and shifter housing where the cable is pulled sideways and then abruptly makes a 90 degree bend. Over time this wears on the outer strands of inner cable - first they thin and then they break.
    You can easily see this if you pull a Shimano polymer cable out after 1000-2000 miles. Usually it will have worn through the 2 outer coatings clear through to the bare steel, but only on one side.
    To extend life, there are a couple things you can do - one, rotate the inner cable 180 so the other side wears. This would involve undoing the rear tension bolt, otherwise it will untwist as soon as you let go. Two, lube the cable occasionally, in this area.
    These are my opinions / experience, as always, YMMV and be different.

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