Porsche started hot dipping their cars in 1976 (not sure if it was only 77 MY 911/912E/924 or if 76 build 76 MY 911/912E as well), which
unfortunately just missed ALL MYs of 914s, because the 76 MY 914s were actually built in the 1975 calendar year. I believe it was a matter of not adding to the overall production costs, lack of customer demand &/or knowledge about the benefits, unavailability of the materials &/or processes/machinery as a result of post-WWII shortages, the lack of European countries using salt on their roads in most cases during that period, or a combination of these.
Remember that German industrial capacity was utterly destroyed in WWII, and then 1/2 of the country was "lost" behind the Iron Curtain - e.g.: Porsche started 356 production outside of Stuttgart in Austria; & BMW's pre/during-WWII plant was lost to the other side & they had to relocate & rebuild in Munich). So the German mfgrs. were literally pulling themselves up by their own bootstraps (with help from the Marshall Plan), and incrementally getting back to being top manufacturers.
But the zinc coatings & galvanizing was only part of the rust story on Porsches & other German cars from that period, as the steel - both in the various steel alloys' composition & raw materials used played a big factor. According to my one Grandfather who had worked at J&L Steel in Pittsburgh PA as an industrial engineer - and who used to lecture me on my 914's inferior steel - post WWII German steel up through the mid-1970's at least, was generally considered inferior to USA steel alloys & quality within each type, mainly due to the higher scrap (recycled) steel content.
And so all 1940s-70's European cars were considered by many in the auto industry to be even more rust prone than their US built contemporaries for the steel alone - aside from galvanizing. Once a few mfgrs. started galvanizing (incl. any of hot dip, spray paint, electroplating, etc.), then everybody jumped on the bandwagon to do it. I think it was the hot dip process & tanks in the assy. line which made it feasible production time-wise & economically viable to rust treat the metals.
Also IIRC, old school galvanized steel is made more brittle for panel stamping & prone to have the galvanization chip off, as well as being toxic when subjected to welding (perhaps more important in the days when people did the welding on bodies - not robots).
Anyway, that's my take on it!
Cheers!
Tom
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