What do you mean by crappy shifting?
Everything on a bicycle works together. Even low end Shimano Tourney equipped bikes can be made to index reliably. The trick is that everything: shifter, derailleur, freewheel, chain and even cable housings all have to match. That's a lot of stuff to have to buy to fix up an old crappy 5-speed bike.
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My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.