Here's the deal. Just got motor rebuilt and a new tranny installed. The car sat for about three months. While the motor was out I installed a vacuum conversion kit. Now the car is running but when I drive it the brakes get stuck. It's fine for the first few minutes and then the car starts to slow down and eventually comes to a complete stop without me touching the brake pedal. Then they won't release! I know it's in the rear brakes because they smoke! The parking brake is fully released so that's not it. I tried a little trick that worked temporarily. While the car was running I loosened the rear line on the master cylinder until fluid came out and the brake suddenly released! The fluid actually squirted out like someone was applying the brake. What can cause this??? Air in the line, bad MC, bad booster?? Anybody seen anything like this?? Thanks in advance for any help!