Thanks for the suggestion, but I removed the calipers one at a time, so it's not that.
I got the new master cylinder bench bled, with no help from the chicken shit bleeder hose kit that came with it, got it in, and bled all 4 corners. A lot of air came out of the lines, but there was minimal improvement, the pedal still goes to the floor without much effort.
I'm about to do some of the tests for the brake booster called for in the TSX shop manual.
Does the brake booster have a high failure rate? I wonder if I can get the master cylinder far enough out of the way without disconnecting the lines...
The booster likely isn't the problem. Alls the booster does is make it easier to push the pedal. If the pedal still hits the floor you've either still got air in the lines or a bad MC.
1. With the engine off, press the brake pedal several times to deplete the vacuum reservoir, then firmly press-and-hold the brake pedal for 15 seconds. If the brake pedal sinks, either the MC is internally bypassing, or there is a leak in the brake system. (mc, lines, prop valve, calipers, wheel cylinders, etc)
2. With the brake pedal pressed, start the engine. If the pedal sinks slightly, the vacuum booster is okay. However, if the brake pedal height does not vary, the check valve or booster is faulty.
3. With the engine running, lightly press the brake pedal. If the pedal sinks more than 3/8" (10mm) in three minutes, the master cylinder is faulty. (If the A/C is on, a slight change in the height of the brake pedal is normal.)