Originally Posted by
grant40
This bike probably originally came with a Simplex rear derailleur, which they did make some bad ones, but most people get the good ones confused with the bad ones and end up throwing them out. I have started hoarding Simplex plastic derailleurs of any kind and plastic Mafac brake levers as I know there will be a time when all of them will be thrown out.
Almost certainly Huret or Shimano, actually.
In the 1970s, Schwinn used "Schwinn Approved" derailleurs manufactured by 3rd parties. Per Mike Sweatman's Disraeli Gears website,
Huret and Shimano supplied those derailleurs. In particular, Schwinn started using a derailleur branded as the "Schwinn GT300 Le Tour" on their top of the line touring bikes in 1973. That was
a rebranded Shimano Crane GS. They'd been using other Shimano models since 1970.
They also started importing bikes from Japan made to their specifications during the 1970s "bike boom". I'm pretty sure that the bikes imported from Japan were lugged and hand brazed. They also used Japanese (Shimano) derailleurs.
The catalog photo of a 1973 Schwinn Super Sport
can be viewed here, as well as the description. The catalog photo also shows a long-cage derailleur.
The frame is also identified as hand brazed; Chicago Schwinn's were not. So the bike is almost certainly a Schwinn-approved bike made in Japan, and the original derailleur on that bike was very likely a Shimano derailleur.