I'm trying to convert my 1988 Bertoni Nuovoitalia from downtube friction shifting to Shimano Index shifting with SIS thumbshifters. At this age it's only got a 6-speed freewheel (14-28), so I got a 6-speed thumbshifter. The original rear derailleur is a Shimano 600 (RD-6207), and I've tried to get it dialed in. It shifts from lower gears to higher gears just fine, but back up to the lower gears is very poor. I thought maybe I needed to get an SIS rear derailleur, so I tried out just a cheaper Tourney SIS (TY-30), and that does just the opposite, higher gears to lower fairly smoothly, but lower to higher is very poor. Question: Will a better quality 6/7 speed SIS RDER like maybe an Ultegra do the trick? Any other suggestions? Appreciate any help. Thanks!!
