We Have Floor Pan!

I have mostly finished installing the floor pan on my 356. There are about 20 plug welds left to complete, as well as a bit of finish grinding and a bit more hammering, but the majority of the project is finished. It is a major sense of accomplishment to have come this far, and it is the first time since I purchased the car that you haven't been able to see through the bottom!

The project went pretty much by the book, as described in the 356 Registry Technical and Restoration Guide. However, for those who don't have access to the book or are just curious how the process went, I will give my own abbreviated version here.

1. To review: before you do the floor pan, there are a lot of other areas that need repair. The floor pan rests on the interior ledges/flanges/sills made up of the inner side longitudinals, the front bulkhead, and the rear bulkhead. It is also spot-welded to a flange running down either side of the tunnel for rigidity and strength. If you haven't already repaired these areas on your car, you need to. See my previous journal entries over the last 6 months to see how I did it.

2. I purchased my floor pan, along with all my other replacement panels, from Restoration Design, but it is the same design as those offered from all the other vendors I know of. The floor pan comes in two sections, front and rear, which are overlapped slightly in the center to form a tubular section. The panels will need to have at 1/2-3/4" or maybe even a bit more trimmed from the sides and perhaps the front and rear to fit your car.

3. Take careful measurements of the interior dimensions of the floor pan area. You can use this to determine how much to trim from the replacement panels after measuring those in turn. Alternately, and perhaps better, would be to jack up each replacement panel into the proper position beneath the car, pressing it against the bottom with a couple of bottle jacks and sections of 2x4 to distribute the pressure. Lean into the inside of the car and scribe/magic marker the inside border of the floor pan. Now, you can trim around the floor pan, adding 1/2"-3/4" width (or whatever the width of your sills are) to the outside of the line you scribed, so that the floor pan will actually rest on the sills of the inner longitudinals and bulkheads.

4. Trim the panels with air shears, nibbler, cut-off wheel, whatever does the job quickest, in the straightest lines, that you have. Trim less than you think you should, and re-measure as in step 3 to make sure you did it right. Easier to take another pass, and trim off more metal, than to cut too much and find out you have made the replacement panel too small for the opening.

5. Punch holes around the perimeter of the replacement floor pan panels with your punch tool you use for plug welds. You will not be able to do plug welds inside the tunnel area very easily, because access is limited. I skipped making plug welds in this area, instead choosing to lap-weld the front center area from beneath, and the rear center area beneath the access area for the transmission coupler.

6. Using a helper (it is much easier with a helper!), slip the rear section of the floor in from the bottom of the car, overlapping the side opposite you on the inner longitudinal. Now, to get the thing in place, slowly and carefully bow the part you are holding up towards you, pulling the panel towards you at the same time. If you do it right, the panel will fall into place on top of the sills, and not be bent. If you do it wrong (and you will), the panel will not reach your side of the sill and will want to fall through; you will have to repeat the process. Make sure you don't permanently bend the floor, you just want to bow it slightly.

7. The front section slides in beneath the rear section. Repeat the process outlined in step 6.

8. Make sure that you have a good fit of both panels. The middle section of the front and rear panels should overlap and form a length-wise "tube" which fits underneath the bump-up in the tunnel edge. If either piece is too far forward or too far backward, you have more trimming to do. Likewise if the pieces aren't sitting centered, and any of the reinforcing stamped sections are resting on a portion of the sill. Take your time, make it right. Once you start welding, it will be hard to go back and re-do anything. If you have to take the panels out to re-adjust/trim, do it now!

9. Jack up both front and rear sections of the floor pan underneath the tunnel with bottle jacks. Spread the force of the jack out over the panel with some sections of 2x4. This is required to get a tight fit against the tunnel, because there is no way to clamp. It also helps straighten the floor pan, which was probably bowed a bit when you slipped it into place.

10. Secure the floor pan to the inner longitudinal sills and the front and rear bulkheads with self-tapping sheetmetal screws. Again, there is really no way to clamp, but you need to insure a tight fit of the body against the floor pan to get good welds.

11. Plug weld on either side of the places you put screws. If you need to get the fit of the areas you are welding tighter than they are before welding, use hammer on top and dolly held underneath to bring them together.

12. If you don't already have your doors installed, put them back on the car now. You need to frequently check that they close properly during the floor pan welding session, to make sure you aren't warping the body with heat. More of a problem on open cars than coupes; I had absolutely no problems. Better safe than sorry.

12. Continue to weld in the pan, using the usual skip-welding techniques to reduce localized heat build-up, paying special attention to heat build-up at the edge of the tunnel if you have left your wiring harness installed! Do not rush, take breaks if things are getting too hot.

13. When floor pan is completely in place, lightly finish grind your spot welds.

Phew! All finished, and hopefully no daylight visible from through the floor anymore.

There are other pieces that attach to the floor pan that now need to be mounted, including the pedal cluster bracket, mounted from beneath, the toe board brackets, and the front and rear seat rail mounts. I will hopefully get to tackle them at the end of the week.

Posted by pbrown at July 7, 2004 10:05 PM