Originally Posted by
AKHIker
Our community groups gets all kinds of bikes to rebuild. We have no issues with front derailleurs on the 42t or the larger road bike ones. Occasionally we have issues with replacing front derailleurs on 48t 3 ring front derailleurs where no matter how low we set the derailleur or how close we set the limit screw it doesn't shift well or won't shift from 2nd into 1st. Guessing it has to do with slightly longer spindle length of some older bikes?
We've tried a variety of moderate priced derailleurs and some cheap ones. Price doesn't make a difference. Sometimes one will be able to be adjusted to work but another needs another 1-2mm you don't have in order to be properly adjusted.
Anyone else have this issue? Any brands that seem to work better in these cases? Or might a derailleur set for 3x8 or 3x9 have enough range to be adjusted for these old 3x7s?
Replacing spindles on these bikes isn't an option. We'll do total rebuilds for high end bikes and collectibles for sale but it's not feasible for the charity ones. Really frustrating when it's an otherwise great condition bike.
Thanks
What's important about spindle length is how it matches with the crankset. The resulting chainline is what needs to be reasonably correct. Common triples went from 45mm, (common in the days of 48T outer ring combos) to more modern specs of 47.5mm or more (to better match 135mm rear hubs and larger seat tube diameters). The FDs were made to match this chainline change.
So, you need to check chainlines, and try to match FDs that were designed for such. Older FDs for lower chainlines and more modern for longer chainlines.
Another thing about cranksets that commonly had 48T outers, is that these are commonly older and were not as refined as later designs. It was a known issue and chainrings have been improved to assist.
Below is Shimano's early attempt.
