[Stripes]

On our 1969 Firebird, when bleeding the brakes with a pressure bleeder(at the master cylinder with 10 lbs) I get a great volume of fluid from the front calipers, but barely any fluid from the rear wheel cylinders. Pushing the brake pedal isn't any better, barely a trickle of fluid from the bleeders on either side.

I checked the round brake delay valve (the one with the button in the rear, mounted on the MC) and it appears that the button is seized. However, that valve only delays the application of the front brakes. Does anyone have any suggestions why the rear brake fluid volume is so low? Master cylinder or rear brake hose? I'll replace the delay valve and rear hose tonight and see if it affects the rear, but I can't see how, as they are separate systems.
Any suggestions?