what it sounds like it could be is in the back drum there is a cylinder with a wheel and spring on it, when you pull the hand brake there is a little spring (the one you lost i assume) and bracket that clicks the little wheel over to auto tighten the handbrake,
try taking this spring off and winding the wheel all the way back so its loose (you will be able to tell if you did it the wrong way because it will be hard to turn and the drum housing wont fit on again because the shoes will be pushed out)
this should work because it will stop automatically tightening the drum everytime you pull on the hand brake, if it does work put the spring back on with out tightening the wheel again, if it eventually starts doing it again you might have yo leave the clip off all together.
what happened with my AE82 was the prev owners lost the spring from the left side so only the right side would stay tight.
PS if you would like me to take some pics of what i mean because i did a sh*t house job of explaining it, PM me.
hope i could help!