I was bleeding the brakes on my '83 yesterday and in a mental lapse, allowed the fluid level in the front chamber of the reservoir to get lower than I like. I could still see fluid in the orafice which goes to the PV, but the front chamber was essentially empty. Anyway, after bleeding the brakes my pedal effort is now better than it was, (although not as good as I would like), and I can easily lock up the brakes, which wasn't the case before. I'd imagine pedal effort would be even more mushy than I started with if the master cylinder had gotten air in it. No?

I guess my question would be, how would I know if I inadvertantly got air in the master cylinder and if it now requires bench bleeding?

 

Sometimes you can't tell if air is trapped even if you bleed the brakes over and over again and visually there is no air in the lines. If you let the level of brake fluid get to low you will probably have to bench bleed the master cylinder. The brake pedal will feel a little spongy.