On Sun, 26 Jul 2009 20:22:04 -0700, Jeannot wrote:

> I'm looking at converting a 2004 crown victoria to a convertible. I can
> cut, I can weld, I can paint.
>
> Of course, my objective is NOT an automatic roof, or anything I can
> drive at 100mph, or anything air-tight. It'll be a very occasional
> drive...
>
> Is anyone crazy enough to have attempted something like that? What are
> the challenges?
>
> And people, please, no replies like "can't be done", "I wouldn't do it",
> etc...
>
> Thanks!

I just _can't_ lurk for a while on a newsgroup! I just read a post and
dive right in...

Pretty much since day 1 closed cars have gained a considerable amount of
body rigidity and strength from the roof. With new cars needing to be
light and crash-proof and all the rest this trend has only intensified.

So when stand there with your sawz-all eying the roof you're
contemplating cutting of a pretty major structural member of the car; if
you want to close the doors when you're done you'll have to replace that
strength before you challenge the car with anything even as mild as
_opening_ the doors.

Do Crown Vic's have frames? If so, then your life is eased somewhat, in
that you 'just' need to beef up the frame and (as already mentioned)
brace the door posts so they can't wiggle out of place. If the frame is
channel, boxing it from the cowl to the rear window will probably
suffice.

As soon as the roof comes off your door posts will be floppy; you'll need
to reinforce them _and_ the back of the cockpit. Cars like the '36 Ford
Phaeton and the '40 convertible did this with great big forged members
that braced the door posts to the frame; this works if there's a frame
member that can carry the load but then your road-noise suppression gets
in a big fight with your body rigidity.

Everything is complicated by the fact that you want strength right where
you can't have material. The best way to do it from a purely
reinforcement point of view would be to run a member straight across the
car, but your passengers might object. This leaves you with needing to
make big "U" shaped members that don't weigh much, don't get in the way,
and won't let their tips move appreciably even when you're exerting
considerable force on them.

Your job on the middle door posts will be complicated by the fact that
you need to lend strength not only against in and out motion, but against
fore and aft motion as well.

I'd seriously consider a member that went behind or under the rear of the
front seat that tied the two door posts together -- figure that it has to
stand up to someone slamming a front door at the same time that a ten
year old is swinging on an open rear door.

And finally, keep in mind that you can't learn stuff unless you screw
stuff up, and you can't screw up a project unless you start it.

--
http://www.wescottdesign.com