We had our first deep freeze last night and it seems to have affected my brakes. The first time I step on the pedal, it is solid. I can force it to move down and the brakes still work, but it feels frozen at first. Would this be moisture in the lines or something having to do with the booster/MC?

Is it the front or back that is frozen? are you still running the drums in back? In the past, I had a truck with drums that would sometimes freeze the mechanical parts in the drum do to water being present. sometimes the e-brake mech would also freeze causing the drums to stay engaged. I don't recall doing anything except running with the brake on for a little bit to heat it up and then letting it sit for awhile. sorry couldn't be more help.

Well its just the pedal when first pressed after sitting in something like 20 or below all night. The first time I press on the pedal, it feels like its not going to move. I can apply some decent force and it will go down at which point the brakes feel like normal. After that initial push they work like usual and thats it.

Water freezing in the drum internals, I'd guess.

One reason to not set your parking brake in freezing weather. The shoes may not release fully and you can end up with some really, really hot parts.

When it warms back up, you should probably also bleed the brakes completely, starting with the lines that are longest (rear, front passenger, then front driver) with fresh, never-opened brake fluid. Check your master cylinder cap to make sure it's sealing well, too.

Brake fluid also really likes water, so never allow the system to be open for long, don't use old, opened fluid cans, etc.

John B.