Here's the way I'd approach it...
Lock the brakes up again and then open a rear wheel cylinder bleeder to see if shoes release (check both rear wheels after opening only one bleeder). If that doesn't release them than you have bad wheel cylinders, broken return springs or trash in the cylinder not allowing the piston to retract. If that does releases the brakes, do it again and this time open the bleeder on the Hydrovac...if they stay locked up then it's the rubber hose acting like a check valve.
Hope this helps,
Mike B
