[Walt Fricke]

While flushing my brakes it occurred to me that I can easily measure how much fluid I have pulled out of each caliper. If I knew how much fluid was in the system, I could stop bleeding before I drained either side of the reservoir (I'm thinking about pre-1988 911s, with no clutch MC).

The reservoir holds X, and the two sides of the reservoir (for the front and for the rear) hold X-A and X-B (maybe they are of equal size) below the center divider.

Each line to the front calipers holds a certain amount. The common line to the rear holds a certain amount. The lines at the rear to each side are as close to equal as maybe not to matter, though the right side one is shorter by a bit.

And then the calipers themselves hold something. I'd be inclined to use "pistons fully retracted" (as in changing pads) as the spec, but knowing what it is with very thin pads would be useful.

And so does the MC.

That way, after the turkey baster (I have an alternative - a huge plastic syringe)has removed the old fluid from the reservoir, and you have poured in new, you can determine when you have flushed the left rear, then the right rear (much much less), then the two fronts (right maybe a little bit less). If this is less than what you put in, you are good and can top off the reservoir and call it good.

I have a spare reservoir, so when I have time (leaving on a trip soon)I can measure its capacity easily enough. Knowing the length and ID of the lines should allow calculating that. I can measure the ID of a line, but don't have a full set to measure. I've not fiddled with the calipers to figure out how much fluid is inside them, and don't have one handy. I do have a spare MC somewhere.

Anyone ever tried to figure this?

The 2.7 little white spec book says the brake fluid reservoir holds 0.2 Liters (200 ml). A typical can of fluid is 500ml. Plenty, but the trick is to avoid getting air from an empty reservoir into the lines.