1993 cutlass ciera s brake help please!

hello guys, im new to this forum, help would be appreciated on this.i have a 93 ciera s, and everytime i try to press on the brake pedal the rear brakes automatically lock up and the rear tires skid. what could be the problem, i ckecked the drums the lines, i cant figure out this problem. again any help would be greatly appreciated. thanks
saif

I had the exact same problem on my 92 ciera. I ended up replacing the shoes and it solved the problem. The old shoes looked fine but I guess something wasn't quite right with them.

I am having the same problem on my 92 Ciera. What brand brake shoes did you put it?