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Thread: Front mech woes

  1. #1
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    Front mech woes

    I'm building up a Surly Crosscheck with a mish mash of parts but I can't for the life of me get the front shifting sorted. I'm attempting to run a 48,36,26 Deroe crankset, LX rear derailleur, 12-28 8 speed Sram cassette, Campag Xenon QS 10speed shifters, Shimano RSX triple front mech.
    The back works perfectly but I can't get the front mech to shift to the outermost chainring. The RSX front mech was originally on (and I assume designed for) a 46-36-26 crankset so I thought that it would shift ok with the slightly bigger outer chainring and the multipe clicks on the ergopower levers.
    With the hi limit screw completely loose and pulling the cable by hand, the outer cage only just clears the outer chainring (distance, not height wise) and doesn't shift the chain itself. If I place the chain on the outer ring whilst pulling the cable tight it rubs on the outer cage whilst pedalling.
    Now is it just a case that this front mech doesn't have enough travel? Or do Shimano front mechs just not run with Campag shifters? Or is it a derailleur positioning issue (something I always have trouble with!)? Something else? Recommendations for a new front mech that will run this setup if this one wont?
    Thanks in advance!

  2. #2
    Senior Member Retro Grouch's Avatar
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    What are you using for a bottom bracket? How much space do you have between the chainrings and the right chainstay?

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    I'm using an LX BB (68 113), as was recommended in the crankset manual. Theres 20mm clearance between the big ring and the chainstay. Inner ring is a bit harder to measure, I'd say there's approximately 10mm. Do you think my BB spindle is too long?

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    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by jobe1 View Post
    I'm using an LX BB (68 113), as was recommended in the crankset manual. Theres 20mm clearance between the big ring and the chainstay. Inner ring is a bit harder to measure, I'd say there's approximately 10mm. Do you think my BB spindle is too long?
    10mm to the granny ring sounds pretty wide to me. That's almost 1/2 inch. I'm an old analog kind of guy. I've always set up triples with minimum clearance, maybe 5mm, on the granny ring. That would move your crankset over about 1 chainring's worth and your front derailleur would have the travel it needs.

    Square taper or octalink? If it's square taper I'd try a 110 spindle. If it's octalink I don't know what to tell you because I don't think that the V2 that you need comes any shorter than 113.

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    It does sound like your BB is too long.

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    Quote Originally Posted by tellyho View Post
    It does sound like your BB is too long.
    +1

    Some of my bikes had the small ring so close to the chainstay that you'd have to look closely to see the gap. Maybe 2-3 mm, close enough that I imagined the ring would scrape when the crank flexed. Never did but you get the point.

    cdr

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    It's octalink, yeh. Hmmm, more hassle! Are road and mtb bb's interchangable?
    Would it be worth trying a different derailleur? I had no trouble shifting when the crankset/bb was on my mtb, albeit with a mtb derailleur and shifters. There are some '06 model campag triples going cheap. And they're 31.8 band-on's so with a shim (my seatube is 28.6) would it make the starting position further out? Or is that accounted for in the derailleur design? Thanks for all your advice, I didn't even consider bb length!

    Edit - Reading through shimano technical documents it seems the mountain bike stuff I have has an "applicaple chainline" of 50mm and the road 45mm which would account for the problems I'm having. Anyone know the campag chainline? It's definitely looking like a new bb will be needed...
    Last edited by jobe1; 03-01-08 at 08:15 AM.

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    You can first disconnect the cable and try to move the derailleur by hand. No shifter will be involved. I suspect that a 10-speed front shifter travels a shorter distance compared to an 8-speed one when it moves from one chain ring to another.

    Check if the derailleur doesn't touch anything. For example, the bottom part of the inner plate of the cage can touch the granny chain ring.
    Last edited by Barabaika; 03-01-08 at 09:49 AM.

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    Quote Originally Posted by jobe1 View Post
    Reading through shimano technical documents it seems the mountain bike stuff I have has an "applicaple chainline" of 50mm and the road 45mm which would account for the problems I'm having. Anyone know the campag chainline? It's definitely looking like a new bb will be needed...
    What's your rear triangle spacing? I'm guessing that it's 130mm. I think that the wider chainline for mountain bikes is to compensate for the wider 135mm dropout spacing.

    Road bike octalink is different from mountain bike octalink (except XTR). So that won't work. You might try a mountain bike front derailleur to see if it will adjust outward the extra space that you need.

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    It's actually 132.5mm ("Our Gnot-rite spacing (132.5mm) allows you to run 130mm road hubs and 135mm MTB hubs" - surly.com) but I'm running 135mm wheels in there.
    I'll have a go with a mtb front mech, I was under the impression they were a no go with road levers though?

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