Brakes Question

[Longhorn Al]

I replaced a lot of stuff on all 4 wheels this weekend (drums, shoes, cylinders, most springs). I bled each cylinder. Now when I was driving up and down my driveway to adjust everything, we noticed only the front tires were grabbing. The rear tires kept rolling and didn't seem to be braking.

We listened to it while it was running and I was pumping the brake. A "swooshing" sound came from right behind the booster each time I pumped it.

Could this be the culprit? Or is something else keeping my rear brakes from working properly?

Thanks for any help.