Wow! I had to do that with my Bug several years ago! But I would have to loosen the bolt on the master cylinder piston in order to relieve pressure!
Turned out that the wheel cylinders (drum brakes) were too incorrect. Accidentally installed VW bus parts instead of bug parts...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car