The Chrysler B-Body platform was the foundation for many of the automaker’s most memorable cars from 1962 to 1979. It’s time for a look underneath. 

In a previous feature at Mac’s Motor CIty Garage, we shared the story of the rushed development of the radically downsized 1962 Plymouth and Dodge full-sized cars. (You can read it here.) The hurry-up styling program for the new mid-sized products was seen as a disaster, even by Chrysler’s chief of design at the time, Virgil Exner. He famously called the cars “plucked chickens,” and as sales plummeted he was banished into retirement.

However, the plucked chickens were a blessing in disguise in at least one way. The  chassis platform hurriedly developed for the ’62 cars, which acquired the name B-body at Chrysler in 1964, would remain in production through 1979 and serve as the basis for many of the automaker’s most memorable cars: Plymouth Road Runner and GTX, Dodge Charger, Coronet R/T and Super Bee, Chrysler Cordoba, and many more. On that basis, the B-body platform is worth a closer look.

To take in the big picture, we go one step back to the ’60-’61 Plymouth and Dodge full-sized cars. Chrysler’s first Unibody products launched in 1960, they were conservatively designed using what Chrysler engineers called a “stub-frame” layout to suit the company’s existing production lines. An evolution of the ladder-frame, front torsion-bar chassis introduced in 1957, the ’60-’61 Unibody platform shared a number of the previous chassis components. Note that the two front crossmembers, which support the engine mounts and the lower suspension points, are solidly welded in place on the front frame runners.

For the carmaker’s new compact Valiant, also introduced in 1960, Chrysler engineers had the benefit of working from a clean sheet of paper, and they came up with a completely different Unibody design. Instead of two welded-in crossmembers, they devised a single crossmember that fastened to the frame runners with four specially engineered 5/8-in machine screws, one at each corner. This stamped and welded piece, which carried all the engine and lower suspension mountings in a single unit, was dubbed the K-member by Chrysler Engineering for the obvious reason.

The K-member system offered a number of advantages, including flexibility in engine selection, location, oil pan configuration, and suspension variations. Also: The bolt-in crossmember allowed the engine and transmission to be easily installed from underneath the body shell on the production line, rather than wrestled into place from above.

Due to the shortened development schedule, there was little time to develop a new chassis for the suddenly downsized ’62 mid/full-sized car. But fortunately, there was a suitable alternative: Chrysler upscaled the Valiant K-member Unibody system (above). The designs are essentially the same, including an identical four-point mounting pattern for the K-member, though there’s one difference. On the bigger cars, the frame runners are a few inches farther apart to accommodate big-block V8s, so their K-members are a bit wider, too. The old stub-frame approach was discarded for the B-body (as it later came to be known) as the other elements of the platform track the Valiant Unibody as well, including the spring hangers and body supports. (Undercarriage photos courtesy of Bring A Trailer.) 

Above, here’s what a typical B-body K-member looks like as viewed from the top, engine compartement view.  In the Mopar muscle-era  performance world, K-members are a frequent topic of conversation, since they are widely interchangeable through the model years to facilitate engine swaps and other modifications. K-members for various applications are produced in the aftermarket as well.

All the Plymouth, Dodge, and Chrysler products that were built on the B-body package are too numerous to list here, though we hit on a few earlier. (Also, the E-body Dodge Challenger/Plymouth ‘Cuda was a close variant.) On all kinds of products from Dodge Coronet to Plymouth Superbird, from 1962 through 1979, the B-body was a key element of the Chrysler story. The final products based on the versatile platform were the ’79 Dodge Magnum and Chrysler Cordoba.