I am going to replace my rusty frame at some point on my 71 Conv Cutlass. I had two pretty solid frames at my folks house in AR that I was going to use the best, but some crooks stole them and sold for scrap--probably got $40.

Anyway, I am starting to look for another frame and there is one here on the site in WA but shipping may be a big deal. My other option is to get a coupe frame (which are available fairly frequently) and then get the HPI frame kit to box/strengthen it:
http://www.lateral-g.net/forums/showthread.php4?t=32399

I'm sure this would actually be much stronger than a conv boxed frame anyway. Just wanted to make sure there are no subtle mounting differences between a coupe and a conv? I wouldn't think so, but does anybody know for sure?

 

To answer your basic question, yes, the outer rails of a convertible frame are simply a hardtop frame, so all the mounting points are the same.

As for that HPI frame kit, unless there's some test data proving otherwise, I do not see how it is stiffer than a convertible frame in longitudinal bending. Removing the roof of a car obviously requires frame stiffening in the longitudinal direction to replace the lost bending stiffness. On a beam (which is what the side rails of the frame are), you add material to the top and bottom caps to increase bending stiffness. The boxing sections added to a convertible frame include this additional cap material (think of two "C" sections welded together with the open sections facing each other). Making the hardtop frame into a box helps with torsional stiffness - which is what the HPI kit does - but by itself this does NOT increase bending stiffness. I would not recommend the HPI kit by itself to use a HT frame under a convertible.

 

I'm in the same situation. The frame on my 71 Cutlass Supreme vert is looking tough right behind the front wheels. I would also ask if anyone has clear pictures of the difference between the coupe and convertible frames.

Would the frame work from a similar GM coupe or convertible, Chevelle, skylark or GTO/Lemans?

Any good links to posts or photo albums of swapping a convertible body from one frame to another? Whats the best way to support it during the process?

 

You don't need pictures, simply look at your convertible frame. The only difference is that the convertible frame has the additional welded on sections under the rockers that turn the open channel "C" rails on the hardtop frame into complete box sections. The outer parts of the frame rails under the rockers (and all the rest of the frame for that matter) is identical between the hardtop and convert. The only difference is that these additional "C" sections are welded to the hardtop frame side rails to make it a boxed convertible frame. The "C" sections are welded open end to open end.

 

Are all the frames identical from 68 to 72?

 

68-72 GM Abodies convert frames all interchange.

Henry

 

That aftermarket kit doesn't look like it clears the footwells, or if so, it is very close. I recommend getting the correct boxing pieces--use yours if they are still good, or another convertible frame.