I posted this in body too. Hoping i hit all knowledgable groups.
I have a 69 convert that has severe rot on the frame and needs replacement. Until now i didn't have the floors out to see the frame. I picked up a standard A body frame as the replacement knowing I would have to box it in-thinking making a box. Now that I see what a real convert frame looks like I'm at a loss. I picked up some plate and was going to weld in a 3" piece to close in the new A frame sides. As its just a 350 cruiser I wasn't overly concerned about strength like duff's owner did on his. My question to you is should I still add the plate and then to that weld something like 2x4 square tubing the length to allow for the trans and floor supports to reach? Or should I insert several tubes into the open frame sides, make a web connecting the front and back, and then fill in with plate? Here is the a-body and then whats in the car now. I hand drew the web idea. anything I do will be 1/8 inch plate. Any advice would be greathttp://www.chevelles.com/forums/attachment.php?attachmentid=42598&thumb=1&d=1307754372 (http://www.chevelles.com/forums/attachment.php?attachmentid=42598&d=1307754372)http://www.chevelles.com/forums/attachment.php?attachmentid=42599&thumb=1&d=1307754406 (http://www.chevelles.com/forums/attachment.php?attachmentid=42599&d=1307754406)http://www.chevelles.com/forums/attachment.php?attachmentid=42600&d=1307754434 (http://www.chevelles.com/forums/attachment.php?attachmentid=42600&d=1307754434)

I had a similar situation with a 66 convertible. I used a 66 hardtop frame, and then cut out the original boxed areas from my rusted out convertible frame. I welded in patches to the boxed areas where they were rusted out, and then welded the convertible boxes into the good hardtop frame. Going to be more work, but if done correctly should be as strong as original when done.

thanks I think I will get or fab some up.

you can (sometimes) pick up Elco frames with damage cheaply, and cut out the mid rails, remove the boxing parts and install to your frame.

I got a nice pair of mid rails with boxes to stiffen the frame on my 71 Monte from a 69 Elco for $30. Yes, I need to remove the sections, but they are factory and can be shortened to work.

Aren't all 64-67 frames all similar in wheelbase except for the longer tails on the wagon-Elco frames? Get a nice Elco frame and shorten away.

Good luck,
Tom

Is your existing frame solid enough to cut out the rotted parts and replace those sections with pieces cut off of the donor frame?

Thanks joe. No unfortunately not only are they rusty and around the body mounts are gone but it looks like someone already messed with it at some point. I am going to just use square tubing to mimic the original frame design. Like I said this isn't going to have any high horsepower so I think I will be ok.

horse power should not be an issue. 2x4 square would be massively stronger than the stock frame in any condition.

Frank do you think putting plate to seal off the frame and then welding the 2x4 to that along with the ends is good? Also on square tube with 1/8 or thicker wall what chance is there of warping? I know sheet and thinner will move but will this also where I should keep it cool and move around?