Michael Alvarez

So guys i have a 2004 gmc sierra 2500 hd diesel. So it started with the front driver side. i had a mobil mechanic look at it and he said it was a bad hose and replaced it. that didn't solve it so then he said it was the caliper then. Well I replaced it and everything was good. Not even 30miles of driving I smelled the burn again. BOTH OF THE REARS WERE STICKING OMG! i drove back home and they were cherry red hot. so question should i replace the Rotor? Also when i got home i bleed the rear brakes. they were good, i got fluid to the back so i know i am sending fluid to the rears. So do i have two bad calipers now? i just find it hard to believe thats it!! I have 134000 miles on it only. And i do have the star type bolt in the back does anyone know what size it is? And come to think of it when I was braking driving home when i would push down i would hear a buzzing sound is that normal? and the pedal would go practically all the way down. I had my wife press the brakes pedal and i saw no leaks whatever. Is that just telling me that the rears are bad? please some guide me in the right direction.