Frames were on the way out in American cars in the early '60s. A frame is a set of
steel girders. The engine, radiator, springs, and such all bolt directly to the
frame. The car body sits on top of the frame and is also bolted to it. The body is
usually several pieces bolted together. It is possible to remove the body and still
be able to drive the car. Most pickup trucks still have frames, and these are visible
inside the rear wheel wells under the bed.

In the early '60s, automakers started moving to the so-called "unibody construction".
In this type of car, most of the body is welded together into one piece. Sections of
the body are built solidly enough for the engine, radiator, springs, and such all to
bolt to the body itself. There is no separate frame. One disadvantage of the
technique is the methods required to repair damage. With the older cars, a
"fender-bender" means you must bolt on a new fender. With the new ones, the existing
body must be straightened and patched.

Some cars have what appears to be a frame welded to the underside of the body. Two
with which I am familiar were the Econoline series through about '67 and the '63
Fairlane. Some people call these subframes. There are also cars that have removable
frame-like sections which stiffen up either the frame or the unibody. These are also
called subframes. My '40 Ford has a girder frame with an "X" shaped subframe in the
center.

George Patterson
    If you want to know God's opinion of money, just look at the people
    he gives it to.

Cars were going frameless way before the 1970s.

The first domestic American companies to switch all passenger car production
to unit construction were Hudson in 1948 and Nash in 1949. These companies
merged in 1954 to form American Motors, and all of that firm's production
(except for certain Jeep models) was unibody until the end came in 1987
with the Chrysler buyout.

On the other hand, there are still some cars today built on a frame, such
as Ford's Crown Vic.