Front discs grabbing after booster/master replacement

[1MYTGTX]

A little backstory to my new problem on my new to me ‘67 GTX.
The car was upgraded to pin type front discs from a ‘72 B body. It had a drum brake power booster on it along with a “universal” disc brake master (one with provisions for ports on either side…. Hated the way it looked) It also retained the original drum brake distribution block (no prop valve)
The brakes worked fine. Good pedal feel but required extra pedal effort due to the drum brake booster (which also worked). Pretty much should have left it alone!!!!!!
Fast forward to my brilliant idea to put in a repro Bendix booster (from Cass @ Dr Diff) and swap out the master for a NAPA reman I had in stock from my old Charger ( lines exiting on manifold side) and new lines to when my troubles starts
After bench bleeding the master, gravity and old school “pump & hood the pedal down” bleeding, adjusting the booster push rod correctly with the pin tool I am experiencing the front brakes excessively grabbing at the bottom 2” of brake travel. So hard that it will put you through the windshield. Almost feels like a “2 stage” master.
2 things I can think of is possible air in the system (pedal feels rock solid with no sinking with car off) or could it be possible the distribution block is jammed?
I realize it should have at least the A body disc/drum prop valve that Cass sells but wouldn’t having that prevent the rears from locking up? The problem I am having is just the opposite. The fronts are locking up at certain pedal travel. Super sensitive.

Any ideas?? Sorry this was so long but I wanted to give as much info as possible

 

[Sixpactogo]

First thing I would do is put the correct Proportioning valve on in place of the drum distribution block to see if that fixes your problem. Mis-matching parts is not a good idea. If using a distribution block was a good idea for disc brakes, you can bet the engineers would not have updated to the proportioning valve.

 

[1MYTGTX]

Yes I concur with that statement but it was working fine before I added this booster/master
I think I will try and put the original master back and eliminate that. Sadly already sold the booster.
Should have left it alone!! LOL.

 

[Sixpactogo]

In my experience, I tried using the drum brake booster on my upgrade to front discs. It wouldn't lock any of the brakes. I did some research and found that drum brakes need about 400 psi where discs need about 800 psi to operate because of the volume they require. That is why they created the dual diaphragm booster in the first place. That said, I think you are heading in the right direction. Just need the right combination.

 

[1MYTGTX]

Update....problem solved. Not 1 but 2 faulty boosters. Third booster from MBM Brakes solved my problem. Had to enlarge plate as well as the firewall itself but all is right with the world now..

 

[luckylee]

I am ordering a bendix brake booster from cass for disc brakes. He’s got a new style one that you don’t have to hack up the bracket and firewall to install. $250 plus shipping

 

[1MYTGTX]

I am ordering a bendix brake booster from cass for disc brakes. He’s got a new style one that you don’t have to hack up the bracket and firewall to install. $250 plus shipping

Yep. Those are the 2 I had