Front disk conversion performed - HORRIBLE braking - Please advise.

[Nickrc3]

I recently installed the standard MBM front brake conversion kit on my 68' Charger https://mbmbrakes.com/dbk6272-mp-110-1962-72-mopar-b-e-body-standard-manual-master-front-disc-brake-conversion-kit/ and unfortunately, cannot drive the vehicle due to an extremely soft, spongy and low pedal. In addition, I cannot lock-up the brakes.
I utilize a manual master cylinder, Inline Tubing proportioning valve, and an adjustable proportioning valve installed within the rear brake line. All brake components are new, OEM routing of all lines and hoses, and rear drum linings adjusted tightly (minimum drum scraping while rotating).
So, I'm thinking air in the system, but after five 'deep' bleeds (w/ Mity Vac, over several days) and a consistent fluid stream, still experience the issues. Tried tapping the master cylinder with a rubber mallet to possibly dislodge trapped air bubbles - no luck.
Now, I'm thinking a faulty master cylinder seal issue, bore too larger, or a longshot - that adjustable pedal plunger rod is not set to the proper length.

Please explain how the master cylinder bore diameter may affect the system.
Any other suggestions shall be greatly appreciated. 
Thanks Fellows!

[b5blue]

I bought a bleeder tool that pushes fluid into the master to fix that same issue when I replaced my brake lines. Like this:
"Motive Products 0090 Power Bleeder Tank"

[metallicareload99]

I use a master cylinder with a 15/16" bore with 4 wheel discs. Pedal requires effort but the fronts will lockup with carbon metallic pads. If you used the master cylinder in the linked kit the pedal should be pretty hard to push....

I've always had good luck gravity bleading then vacuum bleeding. I usually start by hooking up the hose and then opening the bleeder and let it flow while keeping the master full and then hook up the vacuum pump to the canister and draw out some more

I once had a remanufactured master cylinder leak internally because the drilled holes were not deburred and they sealing cups got all tore up. Something to consider as a last resort if nothing else works 

[Dino]

You have 2 proportioning valves? Did you bench bleed the master cylinder? Is there a 0.020" gap between the tip of the pushrod and the MC?

[Nickrc3]

Hey Dino. Thanks on replying.
Good to hear from you again. Last time we corresponded you were returning to college, furthering your education. Hope all is well.
Yes, it was suggested by the Distributor of the brake system to utilize a secondary 'adjustable' proportioning valve for the rear system - so I did. I also, carefully, bled the master cylinder, but need to check the clearance of the rod more closely.
I'm still leaning on air in the system, so I may invest in four of those 'speed-bleeders'. We'll see...

[John_Kunkel]

Speed bleeders are an added expense but I love them.

Your symptoms are common with a MC that has a too small diameter. With a small MC, the pedal stroke is longer and the added pressure makes single-piston calipers flex more giving a spongy feel like air in the system. Does your car have the linkage between the pedal and the booster as shown below?

If there is no free play in the pedal, the rear piston won't allow fluid to return to the reservoir and the pedal will be high and hard.

[b5blue]

Rear brakes adjusted fully? 

[Dino]

I recently installed the standard MBM front brake conversion kit on my 68' Charger https://mbmbrakes.com/dbk6272-mp-110-1962-72-mopar-b-e-body-standard-manual-master-front-disc-brake-conversion-kit/ and unfortunately, cannot drive the vehicle due to an extremely soft, spongy and low pedal. In addition, I cannot lock-up the brakes.
I utilize a manual master cylinder, Inline Tubing proportioning valve, and an adjustable proportioning valve installed within the rear brake line. All brake components are new, OEM routing of all lines and hoses, and rear drum linings adjusted tightly (minimum drum scraping while rotating).
So, I'm thinking air in the system, but after five 'deep' bleeds (w/ Mity Vac, over several days) and a consistent fluid stream, still experience the issues. Tried tapping the master cylinder with a rubber mallet to possibly dislodge trapped air bubbles - no luck.
Now, I'm thinking a faulty master cylinder seal issue, bore too larger, or a longshot - that adjustable pedal plunger rod is not set to the proper length.

Please explain how the master cylinder bore diameter may affect the system.
Any other suggestions shall be greatly appreciated. 
Thanks Fellows!

Hey Dino. Thanks on replying.
Good to hear from you again. Last time we corresponded you were returning to college, furthering your education. Hope all is well.
Yes, it was suggested by the Distributor of the brake system to utilize a secondary 'adjustable' proportioning valve for the rear system - so I did. I also, carefully, bled the master cylinder, but need to check the clearance of the rod more closely.
I'm still leaning on air in the system, so I may invest in four of those 'speed-bleeders'. We'll see...

Man time flies! I have since graduated and have been working the same job going on 5 years!

I clicked the link and that adjustable valve in the picture goes somewhere in the rear line. There should not be any other adjustable valves. You will have a distribution valve where everything comes together, but that should not be adjustable. If that's how you have it, and the push rod has the correct length then bleed the system again. If you still have problems change the MC bore. You can gravity bleed by the way.

[Nickrc3]

Thanks on all reply's Gentlemen.
John, always respected your experience and knowledge. You and other's make this site such a valuable resource.  with your assessment of the single-cylinder caliper and MC bore size. I believe the bore is 1-1/8". Also, the braking is currently full manual, no booster.
Dino, I did observe that the factory plunger rod has a good 1/4" of play before the MC bore is depressed. I did not utilize the adjustable rod that came with the kit.
My course of action shall be to replace the pedal rod with the adjustable unit, adjust to .020, re-bleed calipers/wheel cylinders (again!), and continue playing with that rear proportioning valve. I feel this is not set properly as well.

Thanks again Guys. I shall keep you posted...
 

[John_Kunkel]

the factory plunger rod has a good 1/4" of play before the MC bore is depressed.

With the typical 6-1 pedal ratio, that's 1 1/2" of dead pedal travel.

[metallicareload99]

Your valves look good to me , that's exactly how mine are setup. With my manual 4 wheel discs I have very little dead pedal travel using the stock manual 4 wheel drum pushrod. I tried using an adjustable pushrod but it was way too long

[Dino]

Ok the plumbing is good. That's a regular distribution block where the lines come together. No concerns there. That gap between rod and MC might as well be the Grand Canyon!  Definitely fix that. Also check the bore size; 1-1/8" is best for booster applications. 15/16" or 1" is better suited for manual brakes. Let us know how it goes!

[WhiteOnGreen]

Thanks on all reply's Gentlemen.
John, always respected your experience and knowledge. You and other's make this site such a valuable resource.  with your assessment of the single-cylinder caliper and MC bore size. I believe the bore is 1-1/8". Also, the braking is currently full manual, no booster.
Dino, I did observe that the factory plunger rod has a good 1/4" of play before the MC bore is depressed. I did not utilize the adjustable rod that came with the kit.
My course of action shall be to replace the pedal rod with the adjustable unit, adjust to .020, re-bleed calipers/wheel cylinders (again!), and continue playing with that rear proportioning valve. I feel this is not set properly as well.

Thanks again Guys. I shall keep you posted...
 

The distribution block already have a proprtinal valve for rear brakes. The adjustable valve is innecesary I think 

[Dino]

That block does not have a proportioning function. It divides equal pressure to front and rear drums. Front disc cars had one of two additional brass valves that regulated pre-set pressure. The adjustable valve is needed here to adjust pressure to the rear brakes as needed, be it drums or discs.

[WhiteOnGreen]

That block does not have a proportioning function. It divides equal pressure to front and rear drums. Front disc cars had one of two additional brass valves that regulated pre-set pressure. The adjustable valve is needed here to adjust pressure to the rear brakes as needed, be it drums or discs.

 Nope, the regular distribution block is more square, angle pic is hard but the proprtional valve for disc drum is installed. Pay attention to the bottom valve

[Dino]

I stand corrected!