Advice needed on fitting RD rear floor pan at crossmember area Options

[doug_b_928]

I have the RD rear floor pan replacement piece. I'm looking for advice on how best to install it at the trans crossmember area.

I cut out the area underneath the rear trunk reinforcement (because I butchered that area not realizing that it was spot welded on top and to see what it's like inside). I still need to remove the remaining spot welded bit of the original rear trunk floor (didn't have time to do that yet). Here's a pic:



It would be nice to cut the whole thing to blast the inside and epoxy prime it. But, my concern is getting a nice finished edge on the weld seam on the crossmember. As it is now I can cut the RD piece to fit my current hole and most, if not all, of my repair work at the crossmember area would be covered by the new trunk reinforcement. In this scenario I'd just be replaceing the rear floor and the section of the crossmember under the trunk reinforement.

I could spray some cavity wax or some other product into the crossmember to try to deal with the the rust in there. Though, I suspect the better option is to cut the whole thing, which raises another question. If I cut the whole crossmember, what is the best way to make the seam between the RD part and the existing?

Here's a pic of the measurement of the existing crossmember (from where it starts to raise it's profile). From where the profile raises to where it lowers is about 2 3/4".



And here's a pic of the RD part measuring from the same spot. From where the profile raises to the end of the panel (It's just straight on the front end, so doesn't come back down) is about 3 5/16".



So, if I cut the whole crossmember, what's the best way to make the seam? Here's what I'm thinking:

Cut the crossmember but leave enough to flange, flange it, then cut the RD piece to fit over the flange, spot weld to the flange and bead weld the seam, grind smooth as possible then a bit of filler to remove any imperfections. I don't want to spray seam sealer on these seams because it wouldn't look correct. I could leave the RD piece longer in the area of the trunk reinforcement and bend that area in a brake to meet the trunk floor in front of the crossmember.

How would you guys do it?

[jmitro]

I used Eastwood internal frame coating (with the attachment hose and nozzle) AFTER welding the trunk floor in place; my thought process was that trying to paint it BEFORE welding would just burn off the paint in the areas close to the welds. Use the access holes on the bottom to insert the nozzle.

my car is also on a rotisserie, so I can turn it upside down to let gravity do its work and coat the entire inside of the transmission support

[cary]

I used Eastwood internal frame coating (with the attachment hose and nozzle) AFTER welding the trunk floor in place;

Afterwards is always preferred. Doug's going have burn back from the flange in the trunk. Then both sides of the support when he welds the bottom back on. Building the rally cars at Rothsport I'm seeing about and inch of burn back on painted or undercoated areas.
I'd probably spray it all down with the nozzle only before. Weld. Then use the wand thru the holes and do it again after welding.