70 charger disc brake swap...calipers won't release.

[coffeeguy]

In the midst of doing a disc conversion, the kit was basic with no master or proportioning valves. Got a rebuilt master for disc/drum set up and  cannot get any pedal (booster was bench bled)  and the reservoir for the front goes down but no sign of leakage. When  I crack bleeders (with pedal back in  normal position and under no push) I get a big blast of fluid like it was being pushed hard.   I am thinking  the stock proportioning valve is set up for front drums and is hold the line pressure up .  Is line resistance built into the proportioning valve or the master?  Do I need a disc/drum proportioning valve from something newer?  Are there any other  items in the system that could cause this line pressure to remain so high

[John_Kunkel]

Welcome to the board.

There is no prop valve in a factory drum brake system, only a splitter (safety tee). When you bench bled the MC did you get good flow from both outlets with no air bubbles? It kinda sounds like the bench bleed was incomplete. One way to check is to disconnect both lines from the MC and plug the ports....with the outlet ports plugged you should get a rock hard pedal with little movement.

One thing that will trap pressure in the lines is a misadjusted booster pushrod, if the pushrod is adjusted too long it will prevent the rear piston in the MC from exposing the reservoir return port and pressure will be trapped in the front system.

[coffeeguy]

Bench bleed it(twice just to be sure). I undid the boster from the fire wall and tried again the fronts still held pressure.  I then reattached to the fire wall and pump them 3 times and cracked the line going to the front brakes  it was under a lot of pressure judging by the amount and speed fluid leaked out.  Could I have a drum/drum master instead of what  was suppose to be a disc /drum one?

[John_Kunkel]

When I said pushrod adjustment I meant the one at the front of the booster, not the one hooked to the pedal.

With everything in normal position, remove the lid on the MC and have somebody slowly depress the brake pedal...you should see a "burble" in the surface of the fluid in the rear (and maybe the front) reservoir. If not, the pushrod is adjusted too long. If still in doubt, loosen the nuts holding the MC to the booster and allow the MC to move forward 1/4" or so; this should release the trapped pressure.

If the MC has unequal sized reservoirs (large in rear) it's a disc brake MC.

[coffeeguy]

Backed off firewall nuts again and pumped it while it was backed off and it has now responded . I was able to bleed the  brakes.  Thanks for the pushrod hint