which replacement front derailleur for vintage Univega triple?

Discussion in 'Cycling Equipment' started by ruftytufty, Nov 15, 2007.

  1. ruftytufty

    ruftytufty New Member

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    I've got a vintage 1982(?) Univega Gran Turismo, w/triple cranks.

    Front Gearing: 52/48(maybe 47?)/36.
    Friction shifting, 5 cog freewheel. Chain is SRAM PC40.

    At one point a few years ago, the bottom bracket needed replacing, and the LBS didn't have the proper cup-and-spindle replacement, so sold me the longest sealed BB available (can't remember for sure now, but I think it's a 127mm Shimano, and I do remember verifying that it was indeed the longest available).

    The problem is that, since crank/spindle geometries have changed, this spindle is shorter than the one it replaced, and has thus moved the crankset in a few mm. Current chainline is about 42 mm (center of frame to center of middle chainring), while center of frame to center of small chainring is about 33mm. The result is that the front derailleur (a Suntour 4532) doesn't move in far enough to push the chain onto the small chainring. We've tried tweaking that FD in various ways to try to get it to shift successfully between all 3 chainrings, but with no success.

    The inner chainring does clear the frame adequately, and if I manually nudge the chain over onto the inner chainring, it works fine, at least for the rear cogs I'd want to use it with.

    I presume that the "proper" way to fix this is to replace the BB with an old-style cup/spindle job, and could probably get the parts from sheldon brown, if i could figure out the right length (unfortunately, I had disposed of the old spindle by the time I knew I should have measured it).

    But, I'm hoping to keep the cost/work down, so I'm hoping I can just replace the front derailleur with one that will move in a little farther.

    I picked up a Shimano FD-TY22 from a local used bike shop, which would clearly move in far enough, but the mechanism hits the rear tire (didn't realize that until I got it home and took the old FD off).

    So, I'm wondering if anyone could point me at one (or a family/line of FD's) that would likely work. There are various inexpensive vintage FD's on ebay, but none of the available specs I can find tell me how far in the shifter cage will go. E.g.
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=190167590565&ssPageName=STRK:MEWA:IT&ih=009

    Presumably a road triple would be more likely to work, since they tend to have a 45mm chainline instead of 47.5. Needs to handle a 52-tooth chainring, but only a 16-tooth spread from large to small.

    I may end up going back to the local used bike shop, but most of what they had was pretty junky, not cheap, and a no-return policy.

    Thanks!
     
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  2. ruftytufty

    ruftytufty New Member

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    Another thought - a further constraint is that since this bike has half-step gearing, there are only a few teeth difference (4 or 5) between the outer and middle chainring. Most modern derailleurs require a min difference of 10-12 teeth - the inner plate of the derailleur is correspondingly lower than the outer plate. In contrast, the inner/outer plates on my original derailleur aren't much different (see attached photo).

    I'm still hoping someone has an idea on this.
     
  3. gclark8

    gclark8 New Member

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    I have some old FDs in the junk box like that, where are you?

    Why not buy the correct BB spindle?

    I had the same length issue with an old campag crankset, so I replaced the Crankset (TX71) BB, (UN26) and FD (CO51). ;)
     
  4. ruftytufty

    ruftytufty New Member

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    San Francisco Bay Area. Can't you tell by my funny accent? :) Anyway, can't just drop by!

    I may end up having to go that route. But:
    - I'm not sure what the correct length is, since (see orig post), I don't have the orig BB parts, and I haven't been able to find specs for this bike. The parts aren't available locally, so trial-and-error doesn't work well.
    - Part of the motivation is that staying w/ a sealed BB would be nice. Hopefully less work than going back to old-fashioned cup/spindle, and easier to maintain (I do ride this in the rain some).


    Hmm. Partly hadn't done that because of the expense, but that TX71 can be had really cheap. I'd lose a little gearing off the top end, but don't think that would be a problem. What length BB did you use? Is your bike the standard 45mm chainline for a triple?

    Thanks!
     
  5. gclark8

    gclark8 New Member

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    I use 122.5mm BB for road frame and 124.5 for MTB with TX71 cranks.

    Consider an Index cassette with a smaller top gear. I use 7 speed Sunrace 11-24, or Shimano Freewheel 7 speed 11-28 on the older bikes. If your wheel is 27" (630) and not 700c (622) that will help too.

    I have a table in a book with bb lengths, yout LBS should have one too. Pity you are so far away, I could help on this one.

    See also: http://www.cyclingforums.com/t403611.html
     
  6. ruftytufty

    ruftytufty New Member

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    You're being quite helpful! If I can figure out all the pieces, I think I will go the TX71 route. So far:

    - found the specs for the TX71 at Shimano site. They say 122.5 BB for 47.5 chainline, which I think will work fine.
    - current freewheel is a 6-speed, smallest cog is 14t. i think i'd still be fine losing ~8% off the top end. but, i'll look to see if i can find a compatible freewheel with a 13 or 12 cog. since the tx71 has a much smaller chainring than my old 36T, i can also get by with a smaller range on the freewheel. any tips/suggestions on what to look for? (at least to make sure i get a compatible freewheel - i don't want to modify the rear spread). the chain i have is a SRAM PC40, which i can't find any specs on, so i don't know if it is compatible with anything above 6-speed.
    - the FD-TY22 I picked up doesn't clear my rear wheel with the current setup, but it might with the smaller max chainring. it looks like the CO51 is built the same way as the TY22 (part of the mech retracts between the seat tube and rear wheel) so it would likely have the same problem. but, there are lots of FD's available that don't do this, in case the TY22 doesn't work.

    I took a look at the bike you built up - very nice job!
     
  7. gclark8

    gclark8 New Member

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    Put a couple of spacer washers in the rear axle and fit one of these:
    ;)
     
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