Floor pans, unibodies and handling question(s)

[ChallengerHK]

I was up at my brother's place today, looking at the car and doing some planning, and I need to get some advice and draw of the knowledge here.

Some background: first, as some might remember, I had the left front floor plan replaced a few years back. My fault for not checking the work better when I first picked it up, but the work wasn't done well. In the middle the pan sits about 1/2 inch or more above the torsion bar cross member.

Second, as some might also remember, I'm a fan of spirited driving. Might car will not be a boulevard cruiser. On the way up to my brother's I detoured into the country to drive some windy-twisties, even with the Hyundai. With the Challenger, I'm planning on the same.

Third, my brother is a very knowledgeable guy when it comes to cars, but his stuff runs in different directions. He's got a 62 Jeep that my father bought the year I was born which he mud bogs in, and in cars he's more a drag racing guy, so handling is not his forte.

That's the setup. What I'm trying to figure out is what is the best way to address this floor pan issue. Here's what I see as the options, som of which are from my brother:

1) Fab some sheet metal "Slivers" that would be welded between the current floor pan and the torsion bar cross member. My concern is that handling will differ from side to side (which is also my concern as it is).

2) Fab another steel cross member to fit near the current member and reinforce the entire chassis. This would be a flat piece, something like 1/4" steel running from side to side. My concern here is weight.

3) Get another replacement floor pan, cut the one that's in now out, and put the new one in right. My concern here is that the new pan, on closer inspection, the new pan seems to be significantly thinner than the original pans, something like 30%. On the other hand, this may not make a difference.

4) Get pans from a car being parted and replace some or all of the original pans. Other than potential cost I'm not sure if I have a concern with this one.

So what do you guys think?

[72rtchallenger]

I pick 3 or 4 and put the pan in right,,new ones aren't as good but shouldn't make that much difference 

[HP2]

Certainly the best way is to do it over and get everything nice and tight. But, if your in a pinch, you could add spacers to shore up any movement. Doing this eliminates twist, but creates a more difficult fix later. Newer panels tend to be made form high strength steel, so while they are thinner they do retain a high percentage of the original steel's strength.

Have you started checking the car for square and plumb yet? It may not be too far out at present, but it never hurts to verify.

[ChallengerHK]

I don't want to do this more than once, so if it needs to be fixed my thought is fix it before I move on. That having been said, my nephew has good body skills but I don't know about his frame skills. I'll have a talk with him and see if he's up to verifying frame integrity. If he is I can have him do that, but if he's not and I have to farm it out it will probably have to wait.

[HP2]

The factory service books provide a pretty extensive set of reference measurments. I think there may even be a set in the oval track chassis manual as well. Verification isn't difficult, just time consuming with the number of diagonal measurements to be taken and compared.

[ChallengerHK]

I'm getting to a point where I can take a weekend every now and then and head up there to do some work on the car myself. If the issue is time, I'll spend the time and consider it well spent.

Thanks for the feedback. I know about using plumb bobs for point-to-floor distance. For measuring point--to-point distances is a tape measure good enough?

[Hopalong]

I had my car checked for squareness (?) after I tore it down.  It did have all the sheet metal on at the time I threw about 500 punds of sand bags over the front crossmember.  I took it to a body shop that a friend works at and they used their fancy alingment jig.  For reference they used a 67 mustang schematic.  It's pretty close as far how the cars are built.  I think it was worth the time and money.  The plus side is that the guy said it was the squarest old car he has seen.

[HP2]

Yes, a tape measure is accurate enough, so long as you have the sameperson running the smart end at each point to ensure it is copied from the other side.

[ChallengerHK]

Righteous. Assuming that I can get some time to get up there (pretty good assumption) and that the car makes it inside the garage by then (I'd call it 50/50 for this one) I'll check it out.