When I had a flat earlier this year I decided to check the drums on the rear of my '80 C-10. I looked on the back for an adjustment hole so I could back off the self adjuster, nothing.
I was beginning to think it was just my truck, until I read this thread, so now I know what to look for. Thankfully if there is a knock out in the drum itself it should still be there, looks to be the original drum.
Thanks again for all the info, save me alot of cussing
trying to get the damn things off.