Why would the bike stop if you pedal backwards?

Ok then. Just use solvent, baby powder won't do anything. Brake cleaning fluid works, Acetone, paint thinner, certain cleaners like Purple Power, Simple Green, etc, works but you have to rinse with water when done with those types of cleaners, as a last ditch effort if you don't have anything in your garage gasoline will work; just don't be smoking anything when cleaning with gasoline, Acetone or paint thinner! I would take the tire off first before you clean.

I forgot, you need to clean the brake pads too with the same stuff you use on the rims before you use them on the clean rim.