47-55.1 Pressure bleeding

[72Mountaineer]

Using the Motive pressure bleeder on my brakes on the '53, MC/power unit/prop valve is below the floor, stock pedal. Not getting much pressure at all out of the back, front is better, can't really see any air being expelled at all. Rear line has 10lb valve, front has 2 lb, everything is new. The reason for the Motive is typical bleeding isn't working, pedal goes to the floor on hard braking and the thing just doesn't want to stop good. Front discs and S10, rears are 2nd gen Camaro drum, drums are adjusted OK. Is this a typical thing with below floor MC?