Help please....8 to 9 speed

matt21
matt21 Posts: 71
edited August 2013 in Workshop
Hi all

I'm attempting to convert an Orbit tandem from mtb to road triple but hitting a few snags. I've got some aged 5510 STIs deliberately, to keep a smooth cable run; a new chain and 9 speed cassette and the rear is running beautifully.
On the front however it's a bit of a problem. I've had to use a mech converter to use a road derailleur instead of the top pull mtb exage, but shifting is no where near - it seems like the cable throw isn't sufficient. Do I need to change the 8 speed crankset for 9 speed too? From what I've read it seemed I'd get away with what's there although it seems that with 8 speed the chainrings are further apart?

Thanks in advance...

Comments

  • desweller
    desweller Posts: 5,175
    The chainrings are the same distance apart. Are you sure that you've clamped the cable correctly? Many front mechs require the cable to pass over a narrow lip or ledge on the clamp to achieve the correct leverage.
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  • matt21
    matt21 Posts: 71
    Yep - cable is routed correctly I'm pretty sure. In case it helps it's a sora triple (all I could get) and the cable runs over the ledge. Any other thoughts?
  • Monty Dog
    Monty Dog Posts: 20,614
    When you say 'mech converter' do you mean a pulley or a top/bottom pull adaptor? 8 or 9 speed chainset makes little difference - if there's too much slack in the cable to start, then it'll not move it across enough. Have you checked that the front mech can move far enough to shift the chain onto the large chainring? - Road mechs are designed for a narrower chainline than MTB - you might need to fully unwind the lower stop screw on the front mech.
    Make mine an Italian, with Campagnolo on the side..
  • matt21
    matt21 Posts: 71
    It's a top/bottom pull adaptor. High and low screws are adjusted correctly. I'm wondering if the line of the cable from the pulley could be reducing the amount of throw on the derailleur? - don't know if it would make any difference but might try moving the pulley slightly round the seat tube.
  • desweller
    desweller Posts: 5,175
    When the mech is on the small chainring, is there a lot of slack in the cable?
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  • matt21
    matt21 Posts: 71
    No, absolutely none. I even managed to shred one cable trying to pull more tension.
  • matt21
    matt21 Posts: 71
    OK, so I've had a bit of success. There were 2 bb spacers on the drive side. I've removed them and there's now enough travel for the derailleur to ramp up to the outer ring....so far so good! The problem now is that the feathering click of the shifter is acting over the middle ring; ie 1 click from outer to middle, 1 click across middle, 1 click down to inner. Increasing the tension to put the feathering click over the outer ring just stops the chain coming down onto the smallest ring. In some ways it's actually quite good as there's no chain rub at all in middle.....it would still be good to get it right though.

    FWIW, lbs can't understand what could be wrong "it should all be fine?". Any further ideas appreciated.
  • desweller
    desweller Posts: 5,175
    If you wind the bottom limit screw out a bit it should drop onto the small chainring.
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  • matt21
    matt21 Posts: 71
    No it just won't have it :x (never felt the need to use any of these before!) Probably complete c**p but do old 105 s still feather over the outer ring? The gap between first click (down) is quite large but the next seems to be smaller - as though the feather should be over the middle?

    If I increase tension so feathering is over outer ring, no matter how much I release the low limit screw the chain won't fall off the middle.
  • matt21
    matt21 Posts: 71
    Just in case anyone gives a... Just found this elsewhere so it looks like I've had the setup OK pretty much from the start - just used to ultegra 6700 and presumed they all trimmed in the same way.

    "The Shimano 105 and Ultegra 9-speed STI brifters have four positions for the front derailleur. Used with a triple they provide an outer (big ring) position, middle ring position, a middle ring inner position, and a granny ring position. Used with a double they provide two positions for the small and one for the large ring."
  • Ouija
    Ouija Posts: 1,386
    I think you probably hit the nail on the head with your first post. I don't know about road setups, but on mountain bikes nine speed chainrings are placed closer together than on eight speed. Which is why companies like Truvativ recommend using a 9 speed chain on some of their cranks, even if being used on a 8 speed system. Throw a 8 speed chain on Shimano's Deore cranksets, even though advertised as 8/9 compatible, and the chain rubs against the outer ring also (which is why i had to add spacers to the rings back when i was still using 8 speed).

    Because of this, 8 and 9 speed dérailleurs have different pull distances. Certainly, fitting an old 8 speed dérailleur to a 9 speed crank causes the derailleur to move way too far (using the limiting screws doesn't help as it prevents the shifter from actually clicking into gear).

    Again, that's just my experience of 8/9 mountain bike systems. May not be relevant to 8/9 speed road setups.

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