I have 68 xr-7 with a 302 2v engine. The other day when I was taking her out for her daily drive, I started to back out of the garage when the car sorta jumped and made a nice creaking sound. After the creaking was over, the brakes were back to normal, yet they were still very stiff (meaning hard to push). When I got back to the garage I noticed a thick black powder where the brakes were. Could this powder be some sort of brake material and could the brakes just be fogged over.