Hi! I am working on a 70 Challenger. Has poor brake performance with all type parts tried. Different boosters, MC's, calipers etc.
Currently has 2-3/4" (or so) chrysler slider calipers, 11,75" rotors front, Bendix style booster and a proper MC for the set-up (all from Dr.Diff).
Rear discs from Ssbc. Wilwood adjustable prop. valve in rear line and a disc-disc combination valve.

Brake feels normal and grabs great for light breaking, but when pushing the pedal further it is like hiting a wall. Rock hard pedal and not nearly able to lock the brakes on loose gravel! Flat out dangrous to drive in traffic.

I have tried all different settings on the prop. valve without change.
Brake warning light works , but does not illuminate, so I don't think the valve gets tripped.

Feels like the rear brakes are hydro locking and prevent pressure to the front.

Bleeding fron brakes is easy and normal. Pedal will bottom out when pressure bled.
When bleeding the rears I noticed that the pedal not will bottom out but stop where it stops when all is bled, about half way through total travel.

What am I missing here?
Only things not changed is combination valve, prop. valve, hard lines front and calipers, hard lines and hoses in the rear.
All boosters tried worked great and I even plumbed in a vacuumn pump that pulled 20hg to make sure there was no problem in that eria.

Had the combination valve open but could not spot anything obvious wrong.

Really ned help with this one!!!

Thanks