New power disc brakes, soft brake pedal

[Reyals Bemus]

I just installed power disc brakes on my '64. I used Early Classic's conversion kit with dropped spindles. Its a great kit, very complete and very easy to install. It came with a new Raybestos 1 1/8" master cylinder. I'm also running a new MBM 11" booster listed for '67-72 trucks. Had to fab a threaded connector to hook it onto my existing push rod, but other than that it seems to be a nice booster.

Rear brakes remain completely stock. The whole system was in good working order before the conversion. Well... as much as any manual all-drum brake system could be.

The problem I'm having is a very light brake pedal. It seems to go down a couple inches before engaging the brakes. However, when it does, the brakes work really well. The truck comes right to a halt. But there is just no positive feel to the pedal! Before you guys suggest all the usual things, I'll just confirm what I know.

- I set it up for no slack in pushrod. Pedal immediately actuates the booster.
- Correct rod is between booster and m/c.
- Bench bled the m/c profusely.
- Bled the whole system repeatedly using the old school two man method. Open, push, close, release.
- Rear shoes are adjusted properly in the drums. No excessive play.
- No leaks throughout the system. Triple checked.

For testing purposes, I blocked off the m/c ports while it was in the truck. The pedal felt much higher and firmer, so I don't think my problem is in the m/c, but I could be wrong. Upon hooking it back up the rest of the system, it went back to feeling soft and low. Do I still have air somewhere? I've already poured two quarts of brake fluid through it in my bleeding process.

Any ideas?