hard brake pedal cant get back brakes to bleed.

I have a very hard brake pedal on a 71 dart,manual brake car.
cant get the back brakes to bleed.tried one of brake vacuum bleeder kits and still no fluid comin out.tried havin someone pumpin the brakes and nothin.what could be the problem?it has new a master cylinder and lines.

Did you replace the rear brake hose?

Could be a collapsed or damaged hose restricting fluid flow.

Hope this helps