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Rear mech shifting issue

1964johnr1964johnr Posts: 258
edited November 2017 in Workshop
I replaced the cassette, chain and rear mech(shimano Tiagra) on my winter bike which s a Giant SCR 2 circa 2006 and indexing the gears has been a problem. When I put it on the bike stand and use the barrel adjuster on the mech to index, I just can't get it to shift up and down the gears perfectly. I am able to get it to shift up and down through the first few gears, but then it gives me issues with the bigger gears. I can get it to shift well moving down the block, but then it gives me problems moving back up. I have no idea what to try next. Anyone got any ideas ?

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  • cooldadcooldad Posts: 32,601
    Presumably you replaced inner and outer cables as well?

    And the shifter was in the lowest gear when you started indexing?

    Loosen everything and start again.

    And define up and down. Down would be to the bigger cogs, up to smaller.
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  • On the rear mech there are 2 screws, one marked H, and one marked L. If you are having issues getting the chain up to the big sprockets, the L screw needs adjusting. Turn it anti clockwise, until the brifter shift, matches the sprocket. Be careful though, if you over do it, you risk dragging the rear mech into the spokes. If there is an in line tension adjuster in the rear cable ( there very well may not be on a standard Tiagra) turn it forwards ( if horizontally mounted ) or anti clockwise if vertically mounted, before you start messing with the limit screws.
  • imposter2.0imposter2.0 Posts: 11,277
    On the rear mech there are 2 screws, one marked H, and one marked L. If you are having issues getting the chain up to the big sprockets, the L screw needs adjusting. Turn it anti clockwise, until the brifter shift, matches the sprocket. Be careful though, if you over do it, you risk dragging the rear mech into the spokes. If there is an in line tension adjuster in the rear cable ( there very well may not be on a standard Tiagra) turn it forwards ( if horizontally mounted ) or anti clockwise if vertically mounted, before you start messing with the limit screws.

    That's not what the limit screws are for. Ignore the above.

    Meanwhile, check if you have the cable routed on the correct side of the retainer bolt on the rear mech.
  • I didn't replace the gear cable, so I guess this might be the issue.
  • cooldadcooldad Posts: 32,601
    edited November 2017
    Always the first thing to check.

    I buy Shimano SP41 10m at a time, and a dozen or so stainless cables.

    For a couple of £ not worth faffing with. especially when you've just spent shedloads on all the new stuff.
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  • jermasjermas Posts: 484
    Is the new rear mech compatible with the shifters? The newer 4700 rear derailleurs won't work with the older 4600 shifters.
    Also ensure the cable is clamped in the correct part of the derailleur (in the groove). If the cable is on the wrong side of the clamp this will cause shifting problems.
  • imposter2.0imposter2.0 Posts: 11,277
    Imposter wrote:
    Meanwhile, check if you have the cable routed on the correct side of the retainer bolt on the rear mech.
    jermas wrote:
    Also ensure the cable is clamped in the correct part of the derailleur (in the groove). If the cable is on the wrong side of the clamp this will cause shifting problems.

    yep..
  • jermasjermas Posts: 484
    ^^Oops, where are my glasses?
  • imposter2.0imposter2.0 Posts: 11,277
    sorry ;)
  • I think the problem is probably that the current Tiagra (4700) derailleurs are interchangeable with 5800/6800/9000/9100 and are not compatible with your c.2006 Tiagra shifters.
  • It seems from all the comments that I either need a new cable or I have a compatability issue due to the age of my bike. Perhaps the original tiagra shifters are not compatable with the new tiagra rear mech. Maybe it's the cassette which is the problem. I'll try a new cable and index again and see what happens.
  • keef66keef66 Posts: 13,123
    From your description I'd say that it sounds more like incompatibility between shifters and mech; I'm guessing 4400 / 4500 / 4600 shifters and 4700 mech, but I suppose the reverse is also possible.

    Do the gear cables exit from the sides of the shifters (4600 and earlier), or are they all concealed beneath the bar tape(4700)? How many speeds does the RH shifter give you? If in any doubt, peel back the hood on one of the shifters. The model number is moulded into the plastic body near the bar clamp.

    And do you have any documentation that tells you which model of rear mech you bought??
  • The gear cables exit from the side of the shifters and are not secured under the bar tape so it looks like an incompatibility issue between old shifters and a new rear mech. I will clean up the old mech which I replaced and test it on the bike. If the shifting works then I will know that it is an incompatability problem.
  • I was just about to put the old mech back on the bike when I remembered a couple of previous replies which mentioned the cable rooting on the mech as a possible problem. I checked the rooting on my other bike which has 105 components and the cable ran through the back of the cable attachment. When I checked my Tiagra mech, I had rooted it through the front. I re-rooted it through the back, indexed the gears and everything worked well with the shifting up and down and all sorted within 15 minutes. Amazing that such a small thing can have a big effect.
  • 1964johnr wrote:
    I was just about to put the old mech back on the bike when I remembered a couple of previous replies which mentioned the cable rooting on the mech as a possible problem. I checked the rooting on my other bike which has 105 components and the cable ran through the back of the cable attachment. When I checked my Tiagra mech, I had rooted it through the front. I re-rooted it through the back, indexed the gears and everything worked well with the shifting up and down and all sorted within 15 minutes. Amazing that such a small thing can have a big effect.

    Lesson learned then :lol:
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