73 duster Emergency brake?

The funny thing is when I first fired up in the morning and I go to back up. I can hear it making a noise like it's. The back is touching a little bit and then when I drive forward and push on the brakes the back lock up.. But release immediately they don't stay locked up
But it only does it a few times until I drive it and then it doesn't do it. Just first thing in the morning.