I'm sure the treatment varied over the years, but I believe originally, when there was anything used on the frame, it was a satin coating called 'chassis black', not long lasting on exposed areas, and no primer under it, never what we'd now consider "painting", with prep and primer coat ... I've never noticed any evidence of paint under things removed from TF series truck frames
mummdogg - maybe your truck was produced as 'cab/chassis' and the rear section of the frame got the chassis black because exposed
Bill
