Since you have a replacement master cylinder, MPHAutos is right to look for pedal clearance. On some cars, most;y older imports, the push rod in the power booster is adjustable and if it's too long, it will hold the brakes partially applied. A misadjusted brake light switch can do that too.
If this was an older master cylinder and the brake fluid pressure releases when the lines are loosened at the master cylinder, brake fluid contaminated with a petroleum product is a real good suspect. That is a very expensive repair. Anything made of rubber will swell. The lip seals in the master cylinder will grow past the fluid return ports and block them. That will keep the brakes applied, then, as the linings heat up and that heat transfers into the fluid, the fluid will expand and put even more pressure on the system.
Monday, March 21st, 2016 AT 1:53 AM