An example is the Plymouth, Chrysler's entry-level brand that saw production for more than 80 years until it was discontinued in 2011. For many of those years, Plymouth ranked third in sales in the American market. Unfortunately, beginning in the early 1950s, Chrysler Corporation entered a seemingly never-ending period of boom and bust sales levels. The long, complicated story is summarized here.
From around the middle of the 1930s through the 1952 model year, all four Chrysler brands (in ascending price class order: Plymouth, Dodge, DeSoto, Chrysler) shared the same basic body, differing mostly in grille design, trim and length of hood. However, the differences were strong enough to make each brand visually distinctive. For 1953 and continuing into the early 1960s, Chrysler fielded two bodies for its standard size car lines. DeSoto and Chrysler shared one, while Plymouth and Dodge shared the other.
Chrysler was profitable enough during most of the 1960s that its various brands could share bodies while maintaining distinctive looks, in part due to economies resulting from the elimination of DeSoto in 1961. But the 1970s were increasingly difficult for Chrysler, and Plymouths and Dodges soon became almost indistinguishable. Below are some examples of how this played out. Plymouths are shown in the upper image of each pairing, Dodges below.
Even though the basic body was the same, stylists were allowed to create a number of fairly expensive differences. Examples include the profiles of the rear side windows, trim on the body sides, a rear fender micro-tail fin on the Dodge, and different grille details (though the grille openings seem identical).
Shown here are two compact-car models, the Plymouth Horizon and the Dodge Omni. Price differences were small, the Dodge's interior trim might have been very slightly ritzier and the exteriors featured different grille bar patterns and placement of side chrome trim.
We are now a model year away from Plymouth's demise. Above are Neons, Chrysler's compact-car line at the time. Differences between Plymouth and Dodge are insignificant. Badge engineering at its finest.