Is a 65 Starfire conv frame the same as a hardtop frame?

 

If it is like the A body cars it has the center section boxed. I have a 65 hardtop parts car we could compare pictures. I am sure Joe P would know also.

Larry

 

ALL GM convertibles with full frames came with a special frame that had boxed rails under the sills. Unfortunately, this closed box section retained salt and mud, leading to the common rust-out. Non-convertibles typically had open-section frames since the metal roof provided sufficient torsional stiffness to avoid the need for the extra-cost boxed section. In the 1960s you could order a Heavy Duty Frame option on some cars that was essentially the boxed convertible frame installed from the factory under a non-convert body.

And since the question often comes up, it is not feasible to simply weld flat plates to the open section of a non-convertible frame the way street rod frames are boxed. The factory convertible frames were essentially two "C" channels welded open end-to-open end, making a box section with significantly greater torsional stiffness.

Note that a convertible frame IS based on a hardtop frame, and depending on where the rust is on your convertible frame, you can sometimes carefully cut the additional boxing sections out of the old frame and weld them into a hardtop frame, turning it into a convertible frame.

This is a GTO frame, but you get the idea. Note how wide the side rails are with the added box sections welded in place. Also note that these box sections are not rectangular but are contoured to clear the floor pans. Also, since the space between them is narrower than on an unboxed frame, the trans crossmember is unique to the convertible frame.