More brake woes

[cluxford]

Buick

C5 Vette disc front end
Original 13" drum rears
7" Dual booster with Corvette Master.

a bit over a week ago I lost all vacuum and got a super hard pedal

The booster has been playing up for a while, works, doesn't work I just never changed it. Now I had to.

Got a new one. Installed it.

Rears lock almost immediately and pedal is so touchy it's crazy.

Appears in the 5 years of daily driving this the booster never really worked. Or not well anyway, as now this thing is so touchy.

Locking the rears ain't fun. So it had no prop valve in it. I installed one over the weekend.

Bled it, drove it, still locking rears and pedal goes literally to floor before it grabs.

the push rod in the booster where it connects to the master is so hard to adjust. If I use the measuring tool, to adjust it, car drives fine for 20 mins then locks the rears and I can't drive it.

So today I adjusted the rear shoes all the way in, so they are so loose that the park brake cannot even be adjusted (runs out of adjustment) for the park brake to hold.

Again cold driving, pedal to the floor then rears lock up.
20 mins into driving, awesome. Solid comfortable just right pedal, not too touchy, and starts to brake with about a 1/2 press on the pedal, front won't lock but they grab before rears and pulls the car up nicely.

This is driving me nuts. I'm at a loss why cold braking has no pedal and locks rears (even with them adjusted so far inwards the park brake doesn't work) but once everything warms up (20 mins of driving) it's perfect.

Anyone ever had this problem.

Only changes, new 7" dual booster and then an adjustable prop valve to rears.