The worse the weather gets, the more useful it is to have your bicycle running properly. I usually have a few wonky things going on...a kickstand that I have to nudge back into place after riding over a bump, a shift lever that needs to be retightened every few months. I'm sure there are people who would spare no expense and effort fixing these things immediately, but they don't really bother me. I can work around it.
So, when my rear brake line started freezing up earlier this winter, I just used the front brake. It's not the safest thing to do, but not really a problem on dry pavement and moderate speeds. Then came the ice and snow. Riding with compromised traction AND compromised brake management was not okay.
Fortunately, I had just read an explanation of frozen brake cables and how to repair them, courtesy of Bakfiets en Meer. "Blue Belle" was particularly susceptible to this problem due to her brake cable setup: an exposed cable which uses short lengths of cable housing to route around curves. The cable gracefully follows the step-through frame, requiring an extra turn where the top tube meets the seat tube (see photo!).
I ordered new brake cables on amazon.com (for 70 cents each!) since the old one was rusty and frayed at the end. I unscrewed the clamp at the rear brake, which allowed me to pull the cable all the way out, through all of the cable housing bits and finally out of the brake lever. As it came out of the low point section of housing, rusty water poured out. Yuck yuck yuck! I took all of the housing bits and squirted WD-40 oil through them until it ran clear. Then I reassembled it with a new cable. Hopefully the remaining oil inside the housing (and maybe a plastic bag in heavy rainstorms) will keep it from happening again. For now, I am frost-free and good to go.