Coming home from work just now, the brakes on my '85 240 worked fine at first, but I found that if I released and pressed again, the pedal seemed very hard. Seemed like it took at least 10-15 sec for the system to recover after hitting the brakes. It's nearly as cold as I've ever taken the brick out in (-5 F as we speak, or type), and I wonder if the cold makes the booster slow in recharging for another hit. Definitely a bad night for pumping the brakes. What would be other possible causes that I should check out?