What fitting is this?

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Edelmann #258302 is most likely the adapter for your master cylinder. Most parts stores stock them. If the store has a different brand,they should be able interchange Edelmann to their brand.

Thanks for that info. I have purchased something like this and I'll let you guys know if it works out. If it doesn't work I'll have to drop back and punt. Hoping this'll work because I want to focus on the EFI conversion.
 
So I received a 9/16-18 fitting today in the mail. It's the same as the other fittings I have, so that's not it.

I ended up calling dorman and got ahold of a tech. They pulled a drawing and it showed 9/16-20. That a really oddball thread but apparently for a period starting in 73 Chrysler changed to the slightly finer pitched thread. I ordered a couple from summit today. There are very few to even choose from. I picked up both a wilwood branded and an Edelman branded one. Hopefully this works out. Really would like to button this side project up and at least get to drive my new car!

Edelmann 258303 Edelmann Brake Adapter Fittings | Summit Racing
 
You did some better detective work than some of us did. Guess we were blind because the answer was easily accessible. Rockauto shows the front or secondary port to be 9/16-20 on the 1972- 1975 Dart master cylinder, which should have taken us to Edelmann258303. Sorry about that.
 
Test the Edelmann fitting first before making your brake line. I bought one for my later model two-bolt aluminum master cylinder because it has that same weird 9/16-20 thread and the Edelmann fitting was too short. There wasn't enough thread on it to firmly seat the double flare on the brake line to the seat in the MC. I ended up going to the pick-n-pull for the proper fitting.
 
Test the Edelmann fitting first before making your brake line. I bought one for my later model two-bolt aluminum master cylinder because it has that same weird 9/16-20 thread and the Edelmann fitting was too short. There wasn't enough thread on it to firmly seat the double flare on the brake line to the seat in the MC. I ended up going to the pick-n-pull for the proper fitting.
That's exactly why purchased two types. Fingers crossed.
 
For those people that do not want the hassle of using adapter fittings, just do what Chrysler did. Chrysler's oem brake line came with the correct 9/16-20 nut fitting on the brake line, so the adapter is not necessary. Search eBay for 9/16-20 inverted flare tube nut fitting. Of course this means you will have to make your own lines.
 
For those people that do not want the hassle of using adapter fittings, just do what Chrysler did. Chrysler's oem brake line came with the correct 9/16-20 nut fitting on the brake line, so the adapter is not necessary. Search eBay for 9/16-20 inverted flare tube nut fitting. Of course this means you will have to make your own lines.
I made that decision long ago. I even save the nuts off lines for fiture use.
 
For those people that do not want the hassle of using adapter fittings, just do what Chrysler did. Chrysler's oem brake line came with the correct 9/16-20 nut fitting on the brake line, so the adapter is not necessary. Search eBay for 9/16-20 inverted flare tube nut fitting. Of course this means you will have to make your own lines.
Yep, that's what I did. I'm making my own lines pretty straightforward stuff just a bit time consuming.
 
I knew it was 9/16 I just couldn't remember the thread pitch. Glad you found it.
 
I ended up going with wilwood part number: 220-5248.

It's a 9/16-20 inverted flare, straight to 3/16 tube with no other adapter required.

PXL_20210619_102944965.jpg
 
That proportioning valve knob interferes with the voltage regulator. Now I gotta either figure out a new location for the voltage regulator or just go ahead and install the internal reg alternator I have already.
 
... new location for the voltage regulator ...
On my 3 classic Mopars, I mounted the Vreg on the inner fender next to the alternator. That makes the wiring short, simple, and easy to trouble-shoot. I already had "IGN" and "GND" sources there for other things. Smart to run a dedicated gnd wire from the case of Vreg, rather than rely on a rusty sheet-metal screw like the factory did.

I vaguely recall the 9/16-20 thread you dealt with, but its not coming to me. I do have a bag of brake tube nuts from picked cars, all "junk" to wifey, but valuable to me since saves fussing. On all 3 classics, I used the MC from a 1999 Breeze - 7/8" bore & one of the last years for dbl-flare ports. Two are power-assist and one manual brakes.
 
Got the brakes bled and working over the weekend. Plenty of power but too much pedal modulation. I'll probably stick with it for now but eventually probably switch to a 1in bore MC.

By the way I used a new power bleeder. Motive tool pressure bleeder. Man that made fast work of the system.
 
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I was thinking that the valve was plumbed wrong according to this diagram. I am working on the same project and mine was wrong. Larger part of the MC goes to the rear port and the smaller part goes to the rear which is closest to the valve.





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You are correct about that for the most part. The reasons behind that are MC volume for the front port is smaller, and presence of a residual valve. I removed the residual valve because I don't have drum brakes. I had to choose which end got the larger volume. Either way one set of disc brakes was going to have a smaller MC volume. In a daily driver application this is a problem because as pads wear down the fluid level decreases. I'll just be sure to keep an eye on it. I won't be driving it too much anyhow. Maybe when I swap MC to larger piston I'll try to find an equal volume unit.
 
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