How do self bleeding master cylinders work?

[TJ Hopland]

I get how you used to bench bleed a master cylinder with the little loop of hoses.

I really dont understand what is going on with what appears to be the norm now days that they call self bleeding where you just install the plastic plugs and then have some vague instructions about never going more than one inch and maybe slow and maybe waiting between strokes until you see some shooting fluid or maybe not.

Anyone really know what is going on with these things? That last few times I have messed with brakes on both old and not that old of cars has been a real pita to bleed and with the low quality of parts now days its hard to tell where the issue is.

[Wayne Womble 12210]

Two methods will work.  Use the little hoses and lay them over into the reservoir. Keep the hoses below the level of the fluid. Then work the plunger. The hoses will pump fluid but not suck air. A few pumps this way will remove the air from the system.

The other method is to stop the ends of the ports or the little hoses with you fingers. Pump the plunger and let the fluid flow when you push the rod and stop the flow when you release. Use your fingers as a check valve. Its messy, but will do the same job.