Once upon a time UK Fords and German Fords differed. And once upon a time UK Vauxhalls and German Opels differed. Then Ford and GM unified their European operations. How long did that take?
The process began for Ford in 1967 with the creation of Ford of Europe. For GM it is a bit hazier because their UK and Continental brands kept their names. Ford’s UK and German design centres co-operated on the 1972 Ford Granada. For the 1976 version, Merkenich handled the design. After 1976 there were no more UK-only models (Cortina), as one after another the range became uniform on both sides of the channel: Fiesta, Escort, Sierra, Capri and Granada.
If we turn to GM we see more muddle. Opels could be bought in the UK though Vauxhalls did not sell much (if at all) on mainland Europe.
[Above: the merger of model lines; a black dot means an EU-common model.]
GM had Opel and Vauxhall share some elements of the cars known as the 1972 FE-Series Victor and Rekord D. Then for a period the there were grille and lamp differences. By 1979 the UK had no more UK-only cars when the Viva ended production. Opel lost the large KAD cars in 1970 and the EU-common Senator/Royale didn’t really duplicate the sheer imposing scale of the KAD cars. 1977 seems to have been the year after which all new cars in production in Europe were identical models engineered in Ruesselsheim.
What else did I learn? That Ford’s German operation did not have as broad a range of cars as Opel did. I seem to have left the 1968 Escort out of my timeline. It was a Euroford built in Halewood and Genk. Ford’s 1967 amalgamation began the long contraction of Ford’s UK activities: the ending of Granada production, shifting the Sierra to Germany, ending production of the Focus and then Fiesta until finally its manufacturing amounts to engines. The last vehicles made in the UK by Ford were Transit vans – production ended in 2013.
To answer my question, it takes about a model cycle of seven to eight years to unify two ranges of cars under one brand.