non-mopar website, but gives a good summary:
3. Brake Drag
Brake drag occurs when your brake pads fail to release the rotor when you raise your foot from the brake pedal. Drag may stem from either mechanical or hydraulic issues. Mechanical issues include misaligned or corroded brake calipers, improperly installed wheel bearings, or incorrect push rod sizing.
On the hydraulic side of things, brake drag may stem from excessive heat, faulty flex hoses, or problems with the master cylinder piston. Under normal circumstances, when you release the brake pedal, the piston moves back to its resting position. This movement lowers the amount of pressure acting on the fluid, allowing the calipers to open back up.
Yet if a piston has become damaged or misshapen, it may not move smoothly inside of the cylinder. As a result, your brake calipers may not release in sync with your brake pedal. In this case, the only solution involves replacing the master cylinder.
Brake drag may also stem from a master cylinder containing an excessive amount of brake fluid. The master cylinder contains a special reservoir used to house the fluid that flows back in when you release the brake pedal. Yet if the cylinder has too much fluid, this reservoir won't have the space to accommodate the influx. As a result, the calipers remain under pressure and fail to release entirely.