Ok now this one has me puzzled. So far I've experienced several days of sub-zero temps, saturday and sunday low temps were -32 and -37F and the car started however now my brakes are rock hard. I changed the fluid last summer during a caliper change so Ive ruled out ice formation but now Im lost. It takes a lot of force to get my brakes to apply after the cold snap and even after parking in a heated garage (sallyport) no change at all. My vacuum pump is good (diesel) and all the hoses are in good condition. I have strong vacuum present on the check valve and all my other vacuum accy's work just fine. Should I look at replacing my master cylinder or dig further? Never heard of a freeze damaged master but I guess anything is possable or does this sound like a damaged brake booster?

So far my diesel 760 has thumbed it's nose at the cold weather and started just fine at -32F with the only problem being a frozen radiator that left me driving 160 miles with only the heater as a means of keeping cool... Can't figure out why the radiator froze up when the mix tests good for -45F but who knows. Just kept under 65 MPH and the gauge hovered at the 3/4 mark only to cool down at stoplights. The only uncool thing is my stopping ability and Im out of ideas here.

Help maybe?

Thanks in advance

988