So letting the master cylinder level go too low while bleeding one of the wheels means you have to bench-bleed it?

No, you just need to top off the master and start all over............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Once you let a reservoir run low enough, it will suck air and introduce it back into your brake lines. The whole idea behind bleeding the lines is to get the air out. With air in the lines, your brakes feel spongy because you are hydraulically compressing the pockets of air. Fluids are virtually incompressible, so, no air... no compressing, and your foot on the pedal meets with a more solid resistance.

One of these days, I plan to install some of those speed bleed screws to make the bleeding process easier.

Jerry

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There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Well I'm cheap, and used an aquarium airline rubber flap check valve to replace/flush the brakes on my parents car today. Attach to nipple with airline tubing, crack nipple open, start pumping (and make sure you keep the reservoir full).... (and remove all the old fluid from reservoir and fill with new before starting)

Only took me 30 minutes.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Not so, just resourceful.
I'll have to check it out.

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

Why doesn't it also introduce air into the master cylinder?

It does introduce air into the master cylinder. It has to go throught the MC to get to the brake lines. That is why you have to re-bleed the MC plus the brakelines if that happens.

This is all based on personal experience. I found out the hard way.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Thanks.

I was under the impression there were internal nooks and crannies that get bled while bench-bleeding, and then an external circuit directly from the reservoir to the wheel cylinder that gets bled in routine brake bleeding.

Because there is a separate procedure to bleed air from the master cylinder, I figured there must be a somewhat isolated circuit that gets bench-bled.

Probably wishful thinking, since I am concerned about the wear and tear on the new brake lines I made and the probability I will have to get a new rod bushing for the re-installation.

Dude. I suck at brakes.