when I rebuilt the front calipers on my '79 300SD, I bled the empty calipers and lines by just opening the bleedscrew and letting the air come out. Eventually the brake fluid appeared so I closed the bleed screw and did the other side the same way. I made sure the brake fluid reservoir stayed full while doing the "gravity" bleeding operating.

The brakes have worked perfectly ever since, over 6000 miles.
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