Quote:

I still think the prob is in either the booster or the M/C especially if all 4 corners are locking



Absolutely. My FYI was simply a reply to the "shoes installed wrong" comment. I personally do not think that is the O.P.'s problem.

When locked up:

1. Separate the mc from the booster slightly to see if they unlock. If that unlocks them, look to the rod length or booster or check valve.

2. If it doesn't unlock them, crack the hydraulic lines at the master and see if there's trapped pressure (in which case it's a mc issue).

Down to just a blue car now.