Joined: Jun 2005
Posts: 9,625
Likes: 40
From: South of Raleigh, North of New Hill, East of Harris Lake, NC
Bikes: Specialized Tarmac, Specialized Roubaix, Giant OCR-C, Specialized Stumpjumper FSR, Stumpjumper Comp, 88 & 92Nishiki Ariel, 87 Centurion Ironman, 92 Paramount, 84 Nishiki Medalist
I think I know the wobbling you're referring to. I'll bet it only "wobbles" when the freewheel is spinning free, that is, the chain is not driving it. I'll bet, when you put it on the rack and turn the cranks, the wobble goes away. Don't worry about that.
IMHO, replace your freewheel with all the gears. The new chain is telling you the gears are worn and the new chain is not seating correctly. If you don't replace the freewheel (with all the gears) you'll be wearing out chains prematurely not to mention putting up with that slipping in those two gears.
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