I just completely replaced the entire brake system on a '51 GMC 1/2 ton. New master cylinder, new wheel cylinders, all new lines and all 3 new flex hoses. I made a down and dirty master cylinder bench bleeder out of part of the old brake line with its fitting from the master cylinder. I cut the line short and added a piece of clear flex hose to it. Bolt up the old piece of brake line and run the clear hose back into the top. Leave the filler cap off. With the MC clamped in the vise (Level!) fill it with fluid, then gently pump the plunger. You'll see lots of bubbles coming through that line. Keep at it (it takes a while) until you get a completely clear stream of fluid with no bubbles. I then pulled the clear line out of the cylinder and loosely screwed on the cap. I didn't remove the MC bleeder line from the back of the MC.
I took the cylinder to the truck (still full of fluid) and mounted it. My manual says to attach the clevis that holds the push rod to the bottom of the brake pedal first, but I didn't. First I unscrewed my homebrew MC bleeder and ran in the new line from the brake system. Not too much fluid came out. Then I went ahead and set toeboard clearance and hooked up the clevis. Bleeding the brand new system wasn't hard from that point. For my truck it's driver rear, driver front, pass rear, then pass front. Hope this helps.
David Bush
