96 beretta Rear brakes seems to lock up

On my 96 beretta it has 79000 original miles but i have always had a problem with the rear brakes. They seem to lock up and the body of the car in the rear seems to drop down at same time. It does this with the ati lock fuse in and the fuse out. I have replaced the shows several times and at first all seems well then it starts locking up again. Has anyone else experienced this problem.

Im going to assume that your rear wheel cylinders are not leaking any fluid onto the brake shoes which might give a similar symptom...If the brake fluid has never been changed out I would first bleed out the brakes..dont let the master cylinder go empty with no fluid...then if that didnt solve the problem I would change the proportioning valve if you have one....it might be going bad

well i did another complete brake job and still had same problem. Then i found that the rubber brake line that feeds the passenger side caliper was bad. I replaced it and now everything seems fine.

Also you may want to check for straightness.