I've been trying to find a convertible frame to start my build on. Trying to cobble together a 56 98 convertible from a myriad of parts. The biggest roadblock so far is finding a convertible frame. I know that people are successfully turning 57 Chevy 4 door hardtops into convertibles using the original frame. What I'm wondering is this: 1. How close is a Olds 98 4 dr hdtp frame to the convertible frame. 2. Would a Buick Roadmaster Convertible frame from the same years work under the Olds? Not that they seem to be easy to find either. This thing is going to cost me enough as is without having some special frame made for it.
My 55 98 and 56 88 both have pretty hefty frames. Both have big X members, too. On Chevies, only the converts had the X member. Chevy also had an extra piece of 1/4" steel welded under the flame rails on the converts. I think if you used an Olds hardtop frame, and welded in some 1/4 plate under it, it should be enough. Some hardtop models had the same frame as the convertibles, since they were called "hardtop convertible".
I think I answered your question on the Olds facebook page (apologies if that wasn't you). While the frame shape is exactly the same between a convertible and hardtop, the steel thickness of the convert chassis is nearly twice that of the closed car. I think the Buick frame will be completely different, only the windscreen interchanges. Didn't 56 Buicks have coil rear springs rather than leaf?
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