[scottk]

Manual brakes which came factory with metallic pads or shoes also would normally come with a smaller bore master cylinder than their non heavy duty counterparts, to generate the extra line pressure needed... which means a lower pedal. Or they would simply come ONLY with power brakes. Most semi mets will require higher line pressure. The friction properties are not the same, and so are not well suited to a manual brake application, though they do reduce fade.