The brake lines over time start to collapse and when you push brake pedal the fluid pushes the line open allowing fluid to push calipers against brakes slowing the vehicle. When you release the brake pedal the pressure is reduced and start to create a slight vacuum in the line.

The older brake lines will start to collapse not allowing all the fluid out of caliper causing the brakes to drag a bit which over time the friction causes the rotor to heat up and so on..

you have to replace brake lines on both sides, and flush out fluid and refill with new..

that does the trick.. read this on blazer forum site and it worked..

My wife noted smoke coming from the front left tire after she had driven about 20 miles. I replaced the brake pads, calipers, and the master cylinder. The problem still wasn't solved, so I had the car towed to a (supposedly) reliable repair shop. The mechanic said the problem was with a plugged hose, which he subsequently replaced for $101. My wife drove 5 miles from the shop, the brakes were dragging, smelly and smoking. I took the car back and this time they said the problem was in the ABS unit which would cost $750 for just the replacement unit. I hauled the car home and disconnected the ABS unit. The brakes are still dragging!! What now???