3x8 Sora on an older road bike replacement issues

mbrune

I am working on an old bike for a friend and discovered that their front derailleur spring retainer had broken. It’s an older 3x8 Sora, so I bought 3x9 Sora unit and put it on the bike. I have it the correct distance from the large chainring on install (about 1.5mm) and was trying to shift the front mechanism up to the large sprocket and realized that the cage for the derailleur hangs down so low that makes contact with the middle chainring preventing it from shifting onto the large chainring. Trying to figure out why this would be the case I counted the teeth on the chainrings, turns out the middle chainring is 42 teeth, while the large one is 50. My question is, do I need to purchase a double instead of a triple for this application? My concern is that it won’t have enough reach to shift onto the large sprocket if I do buy a two speed derailleur. Looking for advice. Thank you all in advance.

Munsford0

Struggling to see how it's hitting the middle chainring if it clears the outer one by 1.5mm. Can you post a photo?

MattFalle

generally 2mm clearance for front mech, yah?

have you tried raising it to see if a) it clears and b) still works ok?

its front mech so doesn't matter at all if its x7, x8, x9, etc.

Munsford0

Also my experience that they are not too fussy; fitted a 46/36 CX chainset on the winter bike and the bottle cage bolt prevented me from sliding the FD clamp down far enough so it's way more than 2mm above the big ring. Still shifts very smoothly. that's old 9 speed Tiagra.

mbrune

I’ll post a picture later today, will try raising it up, though it will have to be up around 7-10 mm to clear but I need to see what it does. Not too much choice at this point, either try to raise it or order a 2x setup to see if it will work. It’s the rear part of the cage that’s making contact as it dips down much further than a 2x cage does. With the small difference in teeth between the two top gears there isn’t enough clearance for the rear part of the mechanism to get over the second cog when shifting the chain to the large cog. Not sure how a 30x42x50 makes much sense, but then again, I’ve never owned a triple so I have no idea what the optimal would be. Thanks for the help so far.

Munsford0

My old 105 triple is 50/39/30; thought that was standard Shimano offering. Maybe the middle ring's been replaced at some point?

mbrune

Seems like 50/39/30 is the most common, I doubt she changed the middle chainring, but I suppose if she bought it used it’s possible. I thought about changing it to a 39, but I’m not positive that would increase the clearance. I did raise the derailleur tonight and got it shifting. It’s definitely not ideal, though it shifts okay the little knob on the outside of the derailleur that the chain is supposed to slide over hits the chain instead, so I had to adjust it as far out as it would go with the h limit screw. Personally I’m not a fan of triples, if it was my bike I’d spend a few bucks and buy a double for the front. Easier to adjust and simpler to use. Ah well, hopefully it suffices for her and doesn’t drop too many chains to the inside (seems to want to do that as the derailleur sits higher than it should. Also here’s a picture of what I saw when it was properly adjusted at the front (if you can make it out). The silver bit is the backside of the derailleur coming into contact with the middle sprocket. 😬

MattFalle

if you're worried about chsins dropping on the inside you could treat her to a really cheap plastic anti chain dropper thing - probably a fiver off the internet?

mbrune

Thanks Matt, I did purchase one to put on there, really hoping it works well and is enough of a help to keep the chain from popping off often. The most elegant solution is a new middle chainring, but for how she is going to use the bike it’s not worth the $30 or the time.

Thanks all for the input!