i just replaced the rear brakes and they are not holding, i adjusted them to where they were rubbing pretty good , do you have to bleed them?

 

not unless you replaced the wheel cylinders
you might need to adjust them again or the cylinders might be seized
if you did NOT open the system pull a drum, have someone push the brake pedal slowly, and make sure the cylinders are working
Or do you mean the parking brake won't hold???