Any common problems resulting in loose-like brakes?

[azitizz]

Hi there, I have a 85 300TD wagon and have all of a sudden started experiencing looser brakes. They still work but you have to push down further and there doesnt seem to be the resistance there was before. This seemed to happen quite suddenly. When parked (with the car running) and feeling, when I push down on the brakes I can feel when the resistance actually does begin it seems to release even a bit further to the ground after a second or two.

The brake fluid is still full and Ive never known there to be a problem with them before. The weather is pretty cold here (-20 to -25 C) however thats never been a factor before. Any thoughts on where I can begin looking? ( I want to spend as little time as possible outside!) Ill need a heated Garage of course to do any real work though.
Thanks