[unclebubbles]

While you were changing the caliper, did the reservoir run dry from the line dripping? That may be where your air came from. You asked if the master cyl could be bad, well it could, but as long as it stayed full of fluid no air could get in it. How are you bleeding it? If youre using a helper to pump, be sure they know how to do it. I learned that lesson the hard way years ago, and still have the t shirt. Thats when i started doing it by myself . You can buy a kit to do it with, but its easy to improvise with some clear neoprene tubing(that fits the end of the bleeder good and tight), and a fruit jar. You can also use a large syringe. If one ran out of fluid, i like to reverse bleed it, so you dont have to fight with it to get that last little bit from the master cyl, down to the wheel. Air bubbles actually would rather go uphill than down. The syringe(60cc works good) works great for this. I have a stand made , where i can hang the jar, or syringe high enuff to see it, and tell when the air is out. If you do have to put a master cyl on it, make sure you bench bleed it before you put it on. Good luck.
Later
Ed