Originally Posted by
Al1943
The way to check to see if the crankset is in the proper position is to check the "chainline". A triple should have a chainline of 45 mm. This distance is from the center plane of the frame to the center plane of the middle chainring. You can refer to sheldonbrown.com for a chainline description.
Also check to see that the shift cable tension is keeping the FD from moving in enough. This can be adjusted with the barrel adjuster or by loosening the cable at the pinch bolt. But it sounds as if you may have the wrong FD for the crankset. And the FD should fit the down tube without needed a shim. If we knew the size of your chainrings we could make a better recommendation.
Thanks I feel closer to understanding and solving this. I measured my chainline and it is closer to 42.5mm. To reference my measuring I checked my wife's (trek fx 7.2 WSD 2013) and it's about 48mm. No shim in her derailleur for what it's worth. I don't know if I was duped (that's for another thread) but the whole drivetrain has been changed from stock to components from mid 2000's as far as I can tell. The derailleur is a Shimano
Deore XT FD-M761 and crankset is a Shimano Biopace-SG B48. Well the biggest ring says biopace-sg, I don't know for sure about the inner ones. Not sure if it matters but I can tell they're all elliptical. Is the only measurement the number of teeth? By my count it's 48/36/28. From the specs the derailleur is definitely for a bigger seat binder and I can't clamp it down without shims.
I still can't determine whether these are incompatible. Can I just use a spacer in the chainset to make it work? Can I just put in a new derailleur or chainset to make it work? I'm going for a cheap solution that would last at least a year. I've decided to stick with the bike if it makes financial sense, learn more about what I like and don't like before spending a few hundred on tweaking this or going with something different. Thanks for the help.