2002 2500HD Emergency brake cable adjustment

My emergeccy brakes started fading about one year from new, and dealer refused to do any thing about it while still under waranty. Has anyone found a way to adjust the emergency brake cable to tighten the brake. My chevy dealer told me there is no adjustment. I don't have access to a detailed maint. manual. I had a mechanic (non dealer) tell me the adjustment is automatic whenever you back up and apply the brakes it adjusts automatically. I have done that dozens of times with no effect. Eventually I designed and built a cable shortener, and finally I have an effective emergency brake. Any one else had this problem?
Comments?

the adjustment is at the park brake shoes and is not automatic,pull the rear calipers and rotors.youll see a starwheel between the shoes which is the adjustment.

Thanks for the info on adjustment. How come I had to get the straight skinny here? I guess that says something for the Forum. They didn't make it easy did they?
Mel