Yep... it can be a pain in the butt.

Here's a couple tips you might consider.

On the 66 Impala I just did, I split my trunk pan sheet metal at the middle of the rear under brace spot weld line. (Chevelle has the same basic brace structure)

To find the cut lines, locate your underbraces and examine their structure. You'll see they are shallow "C" sections with an "L" on each leg that spot welds to the trunk pan. That's your "split" point for your sheet metal.

locate the spots welds you can see in your trunk pan. That's the underbrace location. Drill thru the trunk pan from above with a small bit to mark and verify that you are in the CENTER of the under-brace leg that is spot welded along the trunk pan. Do this on both ends. Now, using those reference points, pop a chalk line there. Cut the upper pan on that line with a cutoff wheel. Just cut the pan, not the brace!

You will now have a butt joint in trunk floor which is backed by the brace leg. Very easy to weld. Grind out the remaining spot welds on the OLD pan side of the cut you made.

Once I made this cut, I drilled out the L and R spot welds where the pan joins to the quarter lowers, as well as the front to rear brace spot welds. (not replacing the old braces in my case). I cut the trunk pan to wheel well points LEAVING a small amount of lap from original trunk pan where it lapped onto the the wheel well curve...to provide a lap point for the new pan, and I then cut off the "new" lap bends that were part of my replacement trunk pan (my old trunk pan was very solid here, and I wanted to preserve the old spot welds underneath, etc.)

I did the same trick in the front with the brace. Once all spots are cut, the old pan comes right out.

I predrilled my new pan (NOT the underbrace) with 15/64ish sized drill bit to provide start points for spot weld points to the underbraces and used a mig welder set hot to simulate spot weld points on the braces. With this trick, you get an nice clean flat weld when you're trying to simulate factory spot welds. Not to hard and saves a bunch of grinding and mess. Wire brush that metal shiny before you try this! (Yes, I am a weldor)

Splitting the old and new pans at the underbrace meant I was easily able to butt weld the new pan to the old pan at these points. Very significantly, by using this method, the weld joints cannot be seen from beneath. They are hidden by the brace flange. Even the factory spot weld appearance is preserved from below, because the weld is from above. Because it is a "backed" butt joint, it is easy to weld and the new and old pan and are solidly joined to each other and the brace. Easy to weld, easy to hide, and structurally quite sound. Still gotta control your heat on those long butt joints, but the thick brace makes it easier. Then just grind smooth and finish your butt joints on top (in the usual way, and to your level of satisfaction) in the trunk area, and you'll have a strong and invisible repair.

That's how I did it, anyway. Came out nice and invisible from bottom and top.

Cheers

Keith

 

I did the one piece dynacorn and it fit like a glove. You could actually slip it in with both drop offs in place but I had one quarter and drop off to replace anyways

 

Thanks guys. Great feedback!

Ron

 

If you need the part hidden by the bumper, then definitely go with the one-piece pan!!

 

Yes that is the issue. I went with the multi piece and have found that the only way to get the extension is with the one piece as far as I can tell.

 

This is one piece the chinese got right the first time. well worth the money IMHO. break the spotwelds from the tailpanel and remove all but the very forward body bushings throughout the cab. Leave the forward most bushings on the firewall 1/2 threaded, jack up the body with an engine hoist and place a large 4x4 long enough to cover the width of the frame between the body of the cab and frame just before the rear wheels and insert the new pan between the frame and tailpanel. easy as pie.

 

Best I can tellthe full pans are made by one company. SS396 says their's is dynacorn but they have the wrong picture on ss396's site but the dynacorn site is correct. Any comments?

 

seeing that the tooling to stamp these would be EXTREMELY costly, I don't doubt it one bit. others like Goodmark put their names on others products anyway. The only negative thing I have to say about this pan is this: DON"T stand in between the gas tank braces if you've got other work to do. Although the 1 piece pan is supported well via the rear panel, the side body bushings the front crossmembers and such, the thin sheetmetal still will give way with an adult male working in the trunk. It stretches very easily, so a heavy piece of lumber laying across the gas tank braces would be a very good idea.