Originally Posted by blackf3504dr
I would have thought the same thing but when my HR on a Ford F53 chassis did the same thing it turned out to be a bad caliper. It wasn't releasing and caused the brake fluid to boil and that caused the brake fade (the peddle went to the floor), after it cooled off the brake peddle was normal. When it happened to us we were in Ft. Wayne IN. on U.S 3 in heavy traffic and it got my attention real quick !
I just replaced all the flex brake lines on my 91 oshcosh, got them all from mill supply, word of caution, be sure when they send them they have the long flare nut on the part of the tube that goes into the caliper, I did not check and I had the short flare nuts on the rear lines , as soon as we added brake fluid to the resevoir it started to leak out at the caliper, the short nuts are for cars and do not push the flared tube up against it's mate inside the caliper. you will need all 5 lines, there is one I was not aware of from the frame to the rear axle you will need a 7/16 flare nut wrench