Rear mech driving me nuts

Jamey
Jamey Posts: 2,152
edited February 2009 in The workshop
I know I should post this in The Workshop but I'd like some replies before the commute home this evening if possible.

Basically I can't get my rear mech adjusted so that the changes up and the changes down both go smoothly, at the moment I have to choose one or the other. Particularly troublesome are the changes from smallest to second-smallest sprocket and the changes the other way from biggest to second-biggest sprocket. It's not possible to get both of them working it seems.

I noticed this morning that the changes down (ie moving the chain up onto a larger sprocket) were sluggish so I thought the cable might need tightening up. I stopped and as I did a run through the gears I noticed that it wouldn't go into the highest gear (smallest sprocket) at all. this would tend to suggest the opposite cable adjustment (ie that it needed loosening rather than tightening) so I began to think maybe it was one of the limit screws.

Once I got to work I parked up and decided I'd go take a look at it properly in the afternoon, which is what I've just done.

Here's exactly what I've done:
    1) Check cable is entering pinch bolt in a straight line (this was the cause of the problem last time I had indexing trouble). It is. 2) Completely release cable and turn pedals. Chain jumped onto smallest sprocket (highest gear) perfectly so it's not the limit screw. 3) With cable detached, put bike into highest gear, reattach cable, change down one gear and slowly turn barrel adjuster until chain jumps up onto second-smallest sprocket. 4) Go through the rest of the gears, right up onto the largest sprocket. A couple are a bit sluggish in the middle but otherwise it's all fine. At this point I think I might tighten barrel adjuster a little more to fix sluggish changes. 5) Flick the gear down one to get the chain to jump down onto smallest sprocket. 6) Nothing happens. 7) Cue puzzled expression and me repeating this whole process three or four times, only to find there's no way to get changing perfect in both directions.
I've checked the cable is seated correctly everywhere, friction doesn't seem too bad (cable was new a couple of months ago) and any other obvious things I can think of and still no joy.

Please help.

At the moment I've gone for having smooth up-changes (ie smooth changes onto the next smallest sprocket down) as I decided that you can always pull the cable a bit further when changing the other way, but when relying on the spring your only option is to go up a further gear and then back down again.
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Comments

  • whyamihere
    whyamihere Posts: 7,700
    B-limit screw? If the top jockey wheel is too far from the cogs, the chain won't shift. It should be around 6mm. If not, adjust the screw on the back of the mech, by the mounting bolt until it is.
  • Jamey
    Jamey Posts: 2,152
    I'll give that a try before I head off. I did have a quick look and it didn't look too far away but I could have been more thorough so will check again. I'm pretty sure I've currently got it tightened most of the way as my cassette is an 11-32t.

    In the meantime, any more suggestions are also welcome, cheers.
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  • gtvlusso
    gtvlusso Posts: 5,112
    Cable has probably stretched a little. Undo the pinch bolt, pull the cable nice and tight - set the limit screws about half in each one and go from there. Should take about 10 mins to balance a rear mech.
  • Jamey
    Jamey Posts: 2,152
    I'm not trying to be sarky but did you read the whole thing (I know it was a bit long and waffley, sorry)?

    Only I don't think it's the cable tension in itself... I mean, yes, it probably has stretched a bit but I think something else might be going on as well.
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  • alfablue
    alfablue Posts: 8,497
    Sluggish changes to smaller sprockets are usually to do with gunked-up cables, especially in the final bit to the rear mech - very exposed to water ingress. A short term fix, clean and lube, may last 2 weeks if the weather is bad, medium term fix, new cables, very long term fix, fully sealed cables like Transfil Mudlovers - they are totally maintenance free and last for years.
  • Jamey
    Jamey Posts: 2,152
    Ah, new cables... It's tempting. I heard someone mention Gore cables (I think) as being similarly maintenance-free once fitted. Is that true? How do the ones you mention compare?
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  • linsen
    linsen Posts: 1,959
    Dear Jamey

    Give up riding your bike

    Walk everywhere

    :wink:
    Emerging from under a big black cloud. All help welcome
  • Jamey
    Jamey Posts: 2,152
    Heh.
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  • il_principe
    il_principe Posts: 9,155
    Have you pranged/dropped the bike at all recently? Is the derailleur hanger slightly bent?
  • Jamey
    Jamey Posts: 2,152
    jashburnham wrote:
    Have you pranged/dropped the bike at all recently? Is the derailleur hanger slightly bent?

    Nope, the cage (and therefore, I assume, the hanger) is completely straight. I've not had any accidents on the bike so far.

    That was one of the things I checked when I took a look just now but I forgot to mention it, sorry.
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  • iain_j
    iain_j Posts: 1,941
    alfablue wrote:
    Sluggish changes to smaller sprockets are usually to do with gunked-up cables, especially in the final bit to the rear mech

    +1

    Wiping down and oiling just that bit of cable cleared up my troublesome shifting a few weeks ago, when no amount of playing with the adjusters would sort it.
  • el_presidente
    el_presidente Posts: 1,963
    SINGLE SPEED


    it's your only hope
    <a>road</a>
  • MrChuck
    MrChuck Posts: 1,663
    What alfablue said. Another possible solution is to see if you can get hold of a Rollamajig, which is a little gizmo that basically removes that loop of cable heading into your rear mech and a lot of cable drag and dirt issues at the same time (assuming you have Shimano).
    My experience of sealed cable sets isn't that great- I tried Avid Flakjackets and thought they were a waste of time, others may be better though.
  • Jamey
    Jamey Posts: 2,152
    Well I've just done some searching around this forum and I think this is what I'll do...

    Tonight, before the ride home I'll check the B-tension screw and I'll wipe down the final length of cable leading from the chainstay to the mech body. I don't have any lube with me so it'll just be a clean with some tissue but hopefully it'll help.

    If that solves the problem, and it seems the cables are the culprit I think i might try the Transfil Mudlovers. I'd like to try the gore RideOn Sealed ones but a set of those is £80 (for brake and gears) compared to £35 ish for the Transfil ones.

    If it turns out that sealed cables aren't much better for me then I've only wasted £30, which is a lot better than wasting £80.

    One question though - with sealed cables how come they still fit through the same holes as non-sealed ones? You'd think they'd be wider due to the liner around the cable inner... Unless they make the actual metal part of the inner thinner to account for the liner?
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  • ride_whenever
    ride_whenever Posts: 13,279
    Flying snakes are a great sealed system, run them on a few bikes and never had any issues. They've now done a white snake that is lighter and white...
    Neeermad
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  • Jamey
    Jamey Posts: 2,152
    MrChuck wrote:
    ...see if you can get hold of a Rollamajig

    Just had a look, seems like a good idea.

    Two questions:

    1) Why don't they make them anymore?

    2) Does the wheel on the Rollamajig ever clog up or need cleaning?
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  • alfablue
    alfablue Posts: 8,497
    MrChuck wrote:
    My experience of sealed cable sets isn't that great- I tried Avid Flakjackets and thought they were a waste of time, others may be better though.

    Some sealed cables have seals at each end of the outer, Mudlovers have a liner that goes the entire length of the cable, from shifter to mech in one continuous stretch. I have found them to be brilliant, and saved me money for periodic cable replacements avoided, not to mention the hassle and frustration saved. My winter commutes on a mucky path, 14 miles e/w caused cable gunking about once a week till I fitted these.

    Jamey, they fit as direct replacements for standard cables, no problem. The liner is very thin, but effective.
  • MrChuck
    MrChuck Posts: 1,663
    Jamey wrote:
    1) Why don't they make them anymore?

    2) Does the wheel on the Rollamajig ever clog up or need cleaning?

    I think it's because they were made by Avid, who are now part of the SRAM empire and since SRAM's mechs don't have that cable loop in the first place I guess they're a bit redundant. They can still be found on ebay and probably somewhere on this forum if you look around.

    I've never had any clogging problems in a couple of years, although I use mine on my MTB so dunno how weekend mud compares to daily road grime.
  • Jamey
    Jamey Posts: 2,152
    alfablue wrote:
    The liner is very thin, but effective.

    And the metal cable moves inside the liner? I'm surprised it doesn't wear it away if it's that thin. Cool. Well I may be in the market for some of them soon enough, then.
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  • alfablue
    alfablue Posts: 8,497
    Jamey wrote:
    alfablue wrote:
    The liner is very thin, but effective.

    And the metal cable moves inside the liner? I'm surprised it doesn't wear it away if it's that thin. Cool. Well I may be in the market for some of them soon enough, then.
    Well, it must do eventually, but mine are over 2 years old and running as smooth as day 1.
  • Jamey
    Jamey Posts: 2,152
    Thank you.
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  • marksteven
    marksteven Posts: 208
    hi matey i do 25 miles aday on bike with alfine hub gears . stick it on leave it job done no mechs mines the light blue spe rockhopper on p17 of commuter bike pics
  • itboffin
    itboffin Posts: 20,052
    take it off go single speed :evil:
    Rule #5 // Harden The Feck Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
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  • Jamey
    Jamey Posts: 2,152
    Update: I'm afraid none of the suggestions have worked :(

    I've tried cleaning and lubing the final piece of cable and I've also tried playing with the B-tension screw and neither has sorted it.The rear mech felt pretty smooth along the travel range but I gave it a blast of GT85 anyway. Still no joy.

    I guess I should try replacing the whole cable now but I'm a little reluctant because if it was genuinely the cable causing the problem then cleaning and lubing that loop at the end ought to have provided some improvement, even if it was just for one or two days. But it didn't do anything which makes me think maybe it's not the cable.

    I guess I could find the cheapest, most bog-standard cable possible and try that first to see if it helps before splashing out on a sealed cable.
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  • MrChuck
    MrChuck Posts: 1,663
    Have you had the bike long? Sounds like a similar problem I had on my XTC- for the first few weeks I had it everything was fine, then the shifting went off as you describe and nothing I did would sort it till the Rollamajig. It just seemed to be a mismatch between the mech, the length and bend of that last bit of cable and the position of the cable stop on the seatstay.

    Just thought of something else- sure I heard somewhere you could get stronger springs in mechs so they can push against any drag in the system? Sounds like a huge faff though, even if it's true!
  • Jamey
    Jamey Posts: 2,152
    I always assumed the higher-end mechs had stronger springs in them. Is that not the case?

    TBH you'd think they'd build things that work properly, meaning springs of the correct strength to begin with. I don't think it's the mech that's the problem anyway so replacing that will be the last thing I do.

    At the moment this is the order I'm thinking of trying things in:

    1) Try a new cheap cable and if that works, upgrade to sealed cables soonish.
    2) Try a Rollamajig.
    3) Try a new mech.
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  • alfablue
    alfablue Posts: 8,497
    You should be able to tell if the cable is causing problems by feeling for any friction by operating the shifter whilst pulling gently on the cable whilst disconnected from the mech (but holding it in the same curve as if it was fitted). Any lack of smoothness, then the cable is at fault - outers and inners required.

    I would not expect it to be due to a weak mech spring or wrong mech or anything like that (never come across such problems on new bikes, just ancient, worn out ones), if its not the cable, and the mech is aligned properly then I think it is just setup issues. Have you worked through the Park Tools repair help sections on this? If you work through this methodically you should be able to resolve it - there are no shortcuts if you are a newbie mechanic, with experience you learn to identify the problems more quickly.
  • Jamey
    Jamey Posts: 2,152
    I'm going to pick up a cheap inner and some cheap outer cable on the way home tonight, plus a pair of Park Cable cutters as I don't currently have any. Called the shop and asked them to put the stuff aside for me.

    It's possible the rear cable loop might be slightly short but when I was feeling for friction everything seemed ok to me.

    I'm ok with indexing gears, I've read through Sheldon's method, Park Tool's method and worked through the method I was taught on my maintenance course. All three made/make perfect sense to me and I understand them all. Yesterday I tried a complete re-index from scratch a few times to make sure I was doing it right and none of them helped.

    That's what's confusing me - I know exactly how everything works and what to look for but everything's working fine as far as I can see.

    I'm gonna try this cable (after completely cleaning and re-lubing the mech) at the weekend and cross my fingers. If that doesn't sort it I might have to take it to the LBS.

    Will prob get a Rollamajig too as they sound like a great idea regardless of cables.
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  • alfablue
    alfablue Posts: 8,497
    Well, its weird, you will have been through everything so it may be LBS time. The cable cutters are an invaluable tool, you will get plenty of use from them over the years.
  • Jamey
    Jamey Posts: 2,152
    Yeah, they've been on my list for a while.
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