Hi. I am working on a 70 Challenger that got weak brakes after sitting without bleed brakes for a month. New Bendix booster, MC etc. No change. Ssbc kit. Good pedal and brakes grab good when pressing pedal slightly but no way near locking when stepping on it.
I notice that when bleeding the rears (before the fronts) the pedal does not bottom out - like only 2/3 travel. When doing the front the pedal bottoms out. Is this usual or am I experiancing an obstruction in the rears lines that is hydro locking the system? Like the rear axle rubber hose collapsing?

I just had the same problem and it WAS the rear hose! It had colapsed and NO fluid would go through it at all!

Thanks! How was your rear brakes. acting during bleeding? Mine act normal except the pedal does not go all the way to the floor.

My hose was collapsed so tight that i couldnt get any fluid out of the bleeders at all, therefore the pedal wouldnt drop at all when cracking the bleeders open.

OP, what does your pedal feel like ? mushy like there is still air trapped, or solid like it should feel ? does your booster have an adequate vacuum supply ?

Pedal is normal. Grabs good with light pressure, but when trying to stop fast pedal gets hard and car stops slowly.
vacuum is good. Also tried with a vacuum pump. 18+ hg and no change.
Like said: Feel is good and normal. You really Feel the power assist at light braking but under Heavy braking the stopping force just isn't there. This started after the car sat a few weeks with the front calipers removed.
I noe suspect the proportional valve in the combination valve to act up and block flow under high pressure.
Any other ideas?

SSBC is notorious for poor performing disc brake kits.

there have been several threads on this site about them with pretty much the same symptoms as you are experiencing.

Here's one in the Handling Forum.

Another site offers this thread for your reading pleasure.

Thanks. But this setup worked good. Had some parts off and after putting it back together and bleeding it the stopping force was somewhat gone. Like something blocks the lines when pedal force is increased.