HOW TO REPLACE A TRUNK FLOOR

THIS ’70 DODGE CHALLENGER’S TRUNK HAS SEEN BETTER DAYS. WE SHOW HOW TO CORRECTLY REPLACE THE RUST WITH FRESH STEEL.

Two-piece or one-piece? No, we are not talking about ladies swimwear. We are referring to replacing your trunk floor. In this case, it’s the trunk floor of a ’70 Challenger that needs replacing as part of a factory stock restoration being performed at Muscle Car Restorations in Chippewa Falls, Wisconsin. Most of you probably already know that Dodge didn’t use two-piece trunk floor panels in anything. The only reason to use a two-piece trunk floor, aside from a case where only one side is damaged, is that it is easier to install. It’s not technically correct, but done properly, will serve the purpose just fine. This is especially true if absolute factory correctness is not an issue for you. But what if you want it perfect? Then you’ll need to install a one-piece factory stamping. Trouble is, a one-piece trunk floor will not fit through the decklid opening, hence the original reason for two-piece trunk floors. Another correctness issue to consider is that the original trunk floor panel extends underneath the taillight panel so to do this right the taillight panel needs to be removed first and then placed on top of the new trunk floor. With older restorations in particular, it was common to cut the floor panel off just before the tail panel to avoid disturbing solid panels and, frankly, to save a lot of work. Keep in mind that particularly in mid-western salt states, these cars could show rust damage inside of ten years if they were daily driven throughout the winter, so it’s not uncommon for MCR to receive cars that have outlived their first “restoration” and now not only need repair, but also need some previous “restoration” work to be undone. Such is the case with this Challenger. It was a pretty good looking driver when it came in, but once it was taken down to bare metal one of its issues is a two-piece trunk panel that was, in places, laid over the top of the factory metal. The good news is that Auto Metal Direct (AMD) produces everything that is needed to put this Challenger back to its original factory look.

It’s obvious from the seam running down the middle and the plug welds at the rear of the floor that this part of the floor has been replaced. It’s not bad work really and not all that many years ago this was about as good as one could reasonably hope for. Since then, the trunk extensions have now rotted away so it’s time to pull it all out and make it right again.

Since the tailpanel has also succumbed to the elements, MCR will pull it at the same time so it and the floor can be replaced in the proper order.

Now this is what we call gaining access. Is going this far really necessary? If just the centersection was being replaced, not necessarily, but because the trunk extensions on both sides are bad and the lower part of both wheeltubs will eventually need attention, removing the quarters is a logical step. It’s also easy to see where the repair panel was cut and then plug welded to what is left of the original floor.

MCR used this nifty file belt sander to grind off the plug welds to release the back edge of the two-piece floor. It’s very precise, and it works very quickly.

With part of the trunk gutters also missing, they will be replaced during this project as well.

This might seem a bit extreme, but since new quarters are also needed the tailpanel is cut off just above its base and the whole back part of the body is removed.

With the twopiece floor removed, what’s left of the original trunk floor can be seen. A Blair Rotabroach Spot Weld Cutter is used to remove the original spot welds so the last of it can be discarded.

This is the extreme rear passengerside corner of the trunk floor where it connects to the trunk extension. It’s easy to see that the new (now old) panel was simply laid on top of the cross brace that runs between the rear framerails and was also just welded to the trunk extension panel. This was considered by some to be a satisfactory repair technique years ago but it is obviously not factory correct. MCR will use AMD’s quality panels to fix this.

Once the entire floor has been removed, any remnants of the factory spot welds must be ground flush so the new panel can lay perfectly flat on the framerails.

The inside of the framerails are sprayed with a rust encapsulator to lock up any remaining rust and to seal the surfaces from any future rust formation. Note that the weld surfaces are taped to keep them clean as Copperweld Weld-Thru Primer will be applied to all the spot-weld surfaces.

MCR applies Copperweld Weld-Thru Primer to all surfaces that will be welded together to stop rust from forming in the seams between the panels.

Locating the trunk floor is relatively easy as it simply slides

in between and is positioned by the wheeltubs

The trunk extensions are easily referenced against the trunk floor; clamps and sheetmetal screws are used to hold them in place for now.

Here’s an obscure part you may have never heard about before. It’s a rear crossmember filler bracket that fits between the rear crossmember and the trunk extension. You’ll want to order this along with the rest of the panels you need from AMD so you won’t suddenly discover that you are missing something.

The tailpanel fits on top of and inside the rear lip of the trunk floor and the spot welds are placed on this vertical seam. The same applies for the rear lip of the trunk extensions.

With the trunk floor in position, the tailpanel and trunk gutter scan now be set in place. The tailpanel centers on top of the trunk floor while the trunk gutters can be fairly well aligned by following the flow of the curves on each end. The filler panel, which was earlier positioned by the quarters, and the original trunk gutters now serve as a reference for the new gutters and ultimately the decklid, which will determine final placement of the gutters, quarters, and tailpanel. Final alignment and welding will wait until everything, even the bumper, is mocked up to be certain that it all fits perfectly.