It cost them over $200 million to switch their name from Datsun to Nissan. I could never figure out why. Neither word has any connotation in English: equally null, not positive, not negative, just random pairings of syllables, as far as Americans are concerned. Maybe the words have meanings to the Japanese.
The story I heard, which I could never verify, is that the Datsun name was tied to military production during the war years (as was Mitsubishi and other manufacturers). Somebody decided that was hurting sales. However, by the mid-1980s I don't think anyone in the U.S.A. remembered or cared about the name. After all, Mitsubishi kept their name despite producing the Zero fighter-planes. The Datsun name didn't bother my dad when he bought a Datsun 510 in the 60's, despite having fought in WWII and being part of occupation forces in Tokyo. The war was long over.
No real idea about the name change. My perception at the time, unlike all those here with fond Datsun memories, was the name Datsun was tied to the old “made from beer cans” meme about Japanese products being inferior.
Datsun later shot themselves in the foot with execrable commercials. Awesome! GMAFB