Unable to index rear derailleur correctly - skipping cogs when shifting

Discussion in 'Road Cycling' started by Paul R Williams, Jan 13, 2013.

  1. Paul R Williams

    Paul R Williams New Member

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    Hi,

    I have a 4 month old Team Boardman road bike with Shimano 105 gearset.

    I am learning and understanding the mechanics of road bikes and have read a lot of info online and watched videos and am attempting to set up the indexing correctly on the rear derailleur.

    The H & L limits are set correctly but the indexing is not set correctly. Basically I have 2 problems:

    1. When downshifting (moving to the larger cogs, lowest gear) the shifting is moving the chain 2 cogs at a time. My understanding is that downshifting is caused by increasing the cable tension which pulls the derailleur inwards thus shifting the chain. Therefore this suggests that the cable tension is too tight. Again my understanding is that this is tweeked by turning the barrel adjuster clockwise to reduce the tension.
    However, I have done this and turned the BA, 4 times (1/4 turn each time and it makes no difference). The BA is now turned all the way in so I am unable to loosen the tension any further using the BA.

    2. I also tested upshifting (moving to the smallest cogs, highest gear) and from the downshifting problem indicating a too tight cable, I would expect when upshifting that the derailleur would likely require 2 shifts (as my understanding is that upshifting is caused by loosening the cable, and the spring in the derailleur pulls the derailleur outwards, shifting the chain outwards towards the smallest cogs). However, strangely on the first two shifts from the largest cog, it also jumps 2 cogs although the remainder of the shifting on the final cogs is fine.
    I therefore don't understand how the cable can be shown to be too tight when downshifting and too loose when upshifting as it would therefore be impossible to adjust the cable tension correctly for both downshifting & upshifting.

    I would also note that the chain has been cleaned (it's a relatively new bike so wasn't really dirty anyway) and I have checked the derailleur hanger and it does not appear bent in any way to me.

    I would be grateful of any help as this is becoming quite frustrating.
     
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  2. vspa

    vspa Active Member

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    how did the problem start, after this 4 months ?
     
  3. Paul R Williams

    Paul R Williams New Member

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    Unfortunately I'm not entirely sure. I've only in recent weeks started reading up on adjusting the derailleurs and started to look at mine a couple of weeks ago to see whether they were set correctly, so I'm not sure whether the problem has been there since the start or has occurred since then.
    However, I'm fairly sure that for quite a while I've noticed that it was skipping cogs when downshifting but not sure about the upshifting & I'm not sure whether the problem has become worse.
     
  4. vspa

    vspa Active Member

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    ok when moving to larger cogs, actually the extent to where you move the lever means that you will jump 1, 2 and sometimes 3 cogs at a time when you move down to smaller cogs, then it should be one at a time, of all the years that im using these kind of levers, Shimano 8 speeds and now Ultegra, i have never needed to adjust the indexing after leaving the bike shop, for this reason i actually don't have experience in this kind of mechanicals, other people in the forum will surely help you out,
     
  5. oldbobcat

    oldbobcat Well-Known Member

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    Common problem here. Rather than try to perform message-board triage, let me direct you to the Park Tool "Derailleur Systems" maintenance page.http://www.parktool.com/blog/repair-help/categories/derailleur-systems Read up on Rear Derailleur Adjustments and Rear Derailleur Hanger Alignment.

    My own rear derailleur triage goes like this:
    1. Inspection. Is there visible damage to the derailleur or shifters, or is it excessively dirty, usually gummed up with a clay-like mix of chain oil and dirt? If not, replace or clean. Does the cable slide freely? If kinked, frayed, or excessively dirty, replace. Often on Shimano equipped road bikes the cable will be damaged inside the shifter. Clean out the snibbles and replace.
    2. Align the derailleur hanger. More often than not this is the cause of skipping problems, the result of a fall, or someone hitting it in the bike stand, or somebody backing a Subaru into it in the garage. Some bikes even have bent derailleur hangers right out of the carton.
    3. Set limit screws so derailleur doesn't dump chain into the spokes or the chainstay.
    4. Adjust cable tension so it indexes.
    5. Test ride.
    Works every time.
     
  6. Paul R Williams

    Paul R Williams New Member

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    Thanks for the responses.

    I have already read through the Park Tool site and their info on adjusting derailleur systems.

    2. As indicated I have checked the hanger is not bent.
    3. I have already set the limit screws.
    4. As indicated adjusting the cable tension does not work.
    5. Test ride - I wish I could ! :-(

    1. There's no visible damage to the derailleur or shifters and they're not dirty as I've only had the bike 4 months and have cleaned it after almost every ride ! However, after speaking with someone else the only thing they could think of was a damaged cable somewhere.

    I think I might take it back to the shop as it should be under warranty & I don't want to start messing about with the shifters and cable as I'm not entirely familiar as yet with those features with regards to changing/replacing etc, and I don't want to invalidate any warranty.
     
  7. danfoz

    danfoz Well-Known Member

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    Going back to the shop is a good idea. Question, do you not see the RD hanger moving when you adjust the barrel?

    The movement is minimal, but should still be pretty obvious. Usually skipping beyond the gear you've just shifted to on the rear downshift (and going one extra cog) means too tight. The direction you are turning the barrel to resolve should be moving the hanger toward the smaller cog side. Once the limit screws are set correctly, the indexing barrel usually resolves 99% of shifting problems.

    Sometimes it's tough to triage w/o the subject at hand. Good luck.
     
  8. daveryanwyoming

    daveryanwyoming Well-Known Member

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    It's likely a kinked cable as you suspect, but

    Unless you checked your derailleur hanger with a good tool designed for that it's very hard to know for certain if the hanger is straight in both planes. You can often eyeball the vertical plane but if hangers often develop a bit of a twist where the leading or trailing edge is closer to the wheel and that can really screw up shifting but is very hard to see without something like this: http://www.parktool.com/blog/repair-help/rear-derailleur-hanger-alignment.

    Also based on your description I'd double check that the cable at the rear derailleur is clamped correctly. It's not obvious, but incorrectly clamping the cable can cause some of the problems you're describing as in two gear down shifts for each click of the shifter. Here's a drawing of the right and wrong way to clamp the cable and surprisingly it makes a difference:
    [​IMG]

    Good luck,
    -Dave
     
  9. Paul R Williams

    Paul R Williams New Member

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    Dave you are a Genius /img/vbsmilies/smilies/smile.gif.

    I checked the cable clamp as you suggested and discovered that the cable was clamped between the nut and the washer, not beneath the washer as in the diagram.
    I'm not sure whether it was like that originally or whether I had mistakenly done that when reclamping /img/vbsmilies/smilies/eek.gif, so I put the gears into the smallest cog, unbolted the cable and rebooted as per the diagram, ensuring that the washer was also in the correct position.

    On downshifting it was still jumping 2 or more cogs but now when upshifting it was being 'lazy' (it was doing the opposite before on the upshift). This makes sense from the point of view of a too tight cable for both upshifting & downshifting. I turned the BA a couple of 1/4 turns clockwise to loosen it and hey presto, shifting in both directions is now perfect, moving from one cog to another seamlessly.

    PHEW.......I never would have thought that such a small thing could have such an effect. I presume the cable incorrectly clamped was not allowing the cable to adjust the tension when the BA was rotated.
    On the positive side, I have learned a tremendous amount about setting up the rear derailleur such as limits, indexing, shifting and essentially how it works. On the negative side I missed a good days cycling /img/vbsmilies/smilies/rolleyes.gif.

    Anyway, thanks to everyone who took the trouble to reply. It's much appreciated.
     
  10. jpr95

    jpr95 Active Member

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    Glad it works for you.

    However, your presumption is incorrect. Where the cable is clamped on the derailleur has no effect on tension. The barrel adjuster changes the tension by effectively lengthening or shortening the cable housing. When you screw the BA in, the housing is shorter, which means less tension. When you screw it out, the cable housing is longer, so the tension is higher.

    By changing where the cable was clamped, you moved where the force was applied to the lever arm of the derailler, which changes the amount the derailleur moves with each shift. We're talking tenths of a millimeter here, so it has a huge effect, and the derailleur multiplies the motion. That is, say the cable moves 1 mm, the derailleur moves the chain 5 mm, so anything that changes that ratio can have a huge effect. Move the cable attachment point a little bit out from the pivot point, and that 1 mm of cable movement may only result in 4 mm of chain movement.
     
  11. carrion

    carrion New Member

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    I'm first timer here, so I have yet to really get the level of input. You've been tweaking your barrel adjuster, is that right, and you can't find the dial in that works?
     
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