Lockup works, no reverse

I benched this 518, the owner had it installed somewhere, all 4 fwd gears okay. Lockup works, no reverse, hooked up gauge to rev. Servo port 0 PSI with the selector in rev. Removed gauge, air check it, servo works normal. I do have third gear, I just opened valve body, and the balls are where they belong. If someone could help me out, I'd appreciate it. Could it be the wrong separator plate? Two square holes on big check ball and the one next to it, two square holes are in the middle of the bathtub.