rear brakes locking up

[derail]

I am having a problem with the rear brakes locking up on my '65. I have the e.c.e front disc conversion with spindles,booster,and everything else. The rears are drums from a '72? for 5 lug wheels. Everything on the front and back is brand new including drums, cylinders, etc. The problem is.... when I first bled them (after I bench bled the m/c) I could not get brake fluid to come out of the rears. When I disconnected the brake lines from the rear, there was fluid to the cylinders. So I hooked them all back up and drove it like that for a little while. The brakes were o.k. but not like I would have expected for the upgrades. So, last weekend I had my daughter help me bleed them again. This time, the rears had fluid coming out of the bleeder valves, but the pedal would only go about half-way to the floor. The fronts bled fine. Now if you even barely tap the brakes going down the road, the rears are locking up. I called e.c.e and we have determined that it is not because the piston in the prop. valve is stuck one way or another. I am going to re-bleed them this weekend when I get some help, but in the meantime, any suggestions? Thanks. -Justin