Joined: Feb 2012
Posts: 19,345
Likes: 5,463
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
The issue with residual flux, IMO, is that it absorbs moisture out of the air. Just look at a joint that's sat after brazing w/ flux. Over time the flux will change, it softens and changes from the glassy nature it has after brazing.
It's my feeling that residual flux can speed up any rusting that might otherwise happen, so I like to remove it as best possible or seal it in so no additional moisture can reach it. Andy
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AndrewRStewart