Changed the rear shoes and wheel cylinders on my 97 Yukon 2-3 weeks ago, I'm sure I got air in the lines,,,buttoned up everything,,bled the lines by gravity and the old "you push the pedal and I'll bleed 'em" method. But I was never really satisfied with the results,,after about 2 weeks of driving ( my wife drives it as her D.D. ) I noticed the front wheels brake dusted really bad. I jumped in hit the pedal and it almost travels full stroke before it starts to firm up. So I think,,,master cylinder,,,bled and installed a new master cylinder,,pull and inspect rear shoes and check shoe to drum clearance,, run 3 quarts of brake fluid thru the lines bleeding the brakes AGAIN,,,I get bubbles out of the left rear wheel when I bleed it but I can't tell if it's from the threads of the bleeder screw or the line.I'm on my 4th quart of fluid,,, My shop that repairs our service trucks told me I screwed up when I changed the wheel cylinders and let to much air get into the antilock system,,, The pedal travels almost full stroke and now lights the 'Brake" light on the dash comes on,,,the front pads are in good shape as well as the rotors,,none of the drums or rotors are damaged or have ever been cut.truck has about 80k on it. I raised the rear axle on jack stands and put the truck in gear ,,hit the brakes and the rear tires never slow down,,the emergency brake is good and tight and will stop the wheels in a few clicks,, What the hell am I missing here ?????