I recently lost my brakes, typical of a bad master cylinder. Pedal goes to floor, pump it a few times and it catches sometimes. So, I replaced the master, bench bled it, bled all the lines in the right order, but every time I bleed the left rear I get air. Lots of air. I haven't found a leak of fluid anywhere, and now the brakes act like you would expect brakes with a ton of air to feel. Where should I be looking?

Thanks!

 

Wheel cylinder or caliper in the rear?

regardless if you are getting air, keep bleeding that corner, get it all out sometimes the air comes in passes. I personally always do atleast each corner twice.

If you bench bled correctly I would just stay on that corner bleeding with your partner a few more minutes

 

replace the wheel cylinder or rebuild the caliper.

 

When you write 'just getting air', is that as in air bubbles in a clear hose with bubbles going into fluid in a clear jar? Or just air coming out of a bleed screw? If just the bleed screw, you may think it's air. Have you checked to find if the line from the master cylinder to the wheel isn't clogged with rust?
If you have access to an air compressor, blow air through the line. No air from bleed screw, line is clogged.

 

Sometimes a wrap or two of Teflon tape on a bleeder screw will help. If the bleeder screw doesn't fit the hole tight enough when bleeding, you can get air in through the loose threads.