My latest coffeetable book mentions that Hudson had the first all-steel roof, beating GM to market by a month in late ’34. The ads on this page clarify how it was done. Hudson simply inserted a steel panel for the midsection instead of the wood and cloth that everyone but Pierce had been using all along. GM did it in a more high-tech way, with a new press that formed the roof all in one piece.
BUT: GM retained wood framing in the rest of the body until ’39.
Hudson had already adopted all steel framing for the rest of the body in ’29, ahead of everyone but Dodge. When Hudson switched to the steel roof panel, it was the first in the industry to cut out ALL wood.
I’ve always wondered why most makers kept the soft spot. Even Dodge, the first to eliminate wood studs and rafters in the rest of the body in 1923, stuck with the wood and chickenwire. The Hudson method would have been easier in the ’20s when roofs had a simple curve. The insert would only need to be cut correctly, not pressed or rolled into a compound curve.
Chrysler adopted the Hudson trick in ’36, thus becoming the second with no wood at all.
By ’39 everyone was all steel, and everyone was using the GM method of forming a roof.
Polistra's Mill 