1979 TransAm Rear disc brakes & parking brake

I have a 1979 Trans Am with 4-wheel disc brakes. I've had to replace the rear disc calipers and I can't get the parking brakes to work. Setting the
brake pulls the levers on the calipers OK and the return springs go from uncompressed to fully compressed (so it's not just a simple matter of tightening the cable). The brake sets a bit on on wheel but not at all on the other. I believe that I have the levers set to the correct positon on the hex nut on the end of the parking brake shaft - I'm not 100% sure here but it seems like I can't go another step? The shop manual doesn't give any hints on the proper way to set up the parking brakes. Is there some other adjustment?
Thanks, Mike
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rotor? I recall some Caddy's of about that era had such adjustments--84 Seville, to be one ex. HTH, s
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