73 dart brake problems

Yes, you bleed the M/C first.
There are three ways to do that;
1) if the caliper-pistons are well out of the calipers, you can gently push them back in, one atta time, clamping them in when done. This will force the fluid back up the line and through the M/C chambers, and into the reservoir. The cap better be secured on, or the fluid will fountain up and outta there.
2) You can remove the lines from the M/C install short lines,looped back into the reservoirs, below the liquid line, and start pumping.When no more bubbles come out the loops, you are done.
3) you can fill the reservoirs and tickle the pedal until no more air bubbles pop out. The calipers need to be in their proper locations or the pistons C-clamped in. Tickling involves two persons;one watching and the other tickling. The tickler will gently push the pedal down about a half inch, and release. This will push a tiny bit of fluid down the line, and the release will allow the air to pop back out. The pedal down-stroke may need to be increased slightly, and the stroke-release speed adjusted to make it work. It sometimes takes a bit of fussing to get it to start, but once you figure it out, it goes fast and easy. I do this all the time. Once the air bubbles stop popping out, increase the stroke and repeat. When no more bubbles at all pop up, you should be done. Once the learning is done, it will only take a few strokes to get the air out, or something else is wrong. The whole thing after the learning, shouldn't take but one to three minutes.