How To Install A Trunk Floor

This is the top view of the...        read full caption This is the top view of the trunk floor. B-Bodies are known to have leaky trunks, and this one was no exception. What usually happens is the trunk gets just enough water in it to collect in the ribs under the trunk mat, and there it stays, eventually causing rust holes. The center of this trunk was really bad, and there were a few holes in the sides of the floor as well, so a whole new trunk floor was ordered from The Paddock.

This is the passenger side...        read full caption This is the passenger side of the trunk floor. You can see where water sat in the bottom of the strengthening ribs with the resulting rust etching through.

The first step is to take...        read full caption The first step is to take careful measurements of all the brackets and braces in the trunk floor (such as the spare tire and jack brackets), and draw a diagram of where everything is, as these will come out with the old floor.

Here, Phil Somers is scraping...        read full caption Here, Phil Somers is scraping out the body caulking and seam sealer from between the trunk floors and the inner quarter panel extensions and wheel housing. A screwdriver will work, but a gasket scraper makes it go a lot quicker.

Time Machines has a full rotisserie,...        read full caption Time Machines has a full rotisserie, and the Superbird was on it for this story, but you don&8217t need one at home for this. Phil used a plasma cutter to cut out the rotted floor sections, trimming around the braces and leaving them in place. If your braces are rotted, The Paddock can supply you with new ones. Take the floor out in sections, between the braces. A regular saber saw will also work fine in place of the plasma cutter.

Next, cut out all of the factory...        read full caption Next, cut out all of the factory spot welds that held the floor to the braces and remove what&8217s left of the floor. Spot weld cutters are available from Gearbox Grannies, Eastwood, and a host of other companies.

Here&8217s the top of the...        read full caption Here&8217s the top of the braces after all of the floor has been removed and the spot weld plugs have been ground off.

Because this is a concours...        read full caption Because this is a concours resto, Time Machines coated the inside of all the braces and the rear frame boxes with Ospho, a rust neutralizer. Ospho leaves a protective coating, which makes it more difficult for rust to return. Unless you are doing a concours car, now is great opportunity to coat the inside of the braces and frame boxes with POR-15 for maximum rust protection.

While trunk centers are available,...        read full caption While trunk centers are available, Time Machines opted to replace the whole floor, rather than just the center. Complete B-Body trunk floors are available from The Paddock, and come in two halves--left and right. Here we&8217ve had this half of the trunk floor inside the car and traced the location of the braces with a marker, from underneath the car, onto the repro floor pan.

This is the only part more...        read full caption This is the only part more tedious than drilling the original spot welds out--putting the new ones back in the repro floor. Using the same spot weld cutter, start drilling holes at the perimeter, lined up with the frames and braces outlined with the marker.

After Swiss-cheesing the new...        read full caption After Swiss-cheesing the new floor pan, dress the holes with a grinder, and flatten the area around the new holes with a hammer and dolly.

Spray-Galv, available in aerosol...        read full caption Spray-Galv, available in aerosol cans from most auto body supply stores, is weldable and is used to prep the area along all the seams and welds to inhibit rust.

Eastwood and several other...        read full caption Eastwood and several other companies make weldable primer that will work for this, too. Again, it depends on if you’re concours restoring the car, and whether or not you can paint the bottoms of the floors when you&8217re done.

We sprayed the seams where...        read full caption We sprayed the seams where we drilled the spot weld holes, and the tops of all the braces and frame boxes that we would be welding the floor pans to.

After the weldable primer...        read full caption After the weldable primer dries it&8217s time to set the floor sections in place. Note that we also drilled spot weld holes in the down-standing flange along the fender-side edge of the floor pan.

Use tin snips to trim any...        read full caption Use tin snips to trim any excess metal. Trim in small amounts, because it’s easier to remove metal than it is to add it when you&8217ve cut too much.

Once the floor pan is trimmed...        read full caption Once the floor pan is trimmed and set into place, the spot welding starts. Here, Phil is pointing to the front-most corner on the driver’s side, by the wheel housing. This is the edge of the floor pan that has the down-standing flange. One welder’s Vise Grip underneath holds this flange to the bracing underneath the car. If you don&8217t have Vise Grips that fit this, a friend applying pressure with a piece of wood to keep the panels in alignment also works.

Start filling the spot weld...        read full caption Start filling the spot weld plugs. Here Phil is using a hammer handle to make sure that the new trunk floor is tight against the brace it&8217s being welded to.

The trunk floor halves come...        read full caption The trunk floor halves come out of two separate dies. Running left-to-right in the middle of the trunk is a strengthening rib. Depending on where you trimmed, yours might not line up exactly perfect. Also, the rib doesn’t go to the very edge of the panel in the center of the trunk floor, so there&8217s a small flat spot where they meet. A concours car will have the edges hammered and mated perfectly. On a driver, the whole thing is simply covered with the trunk mat.

After grinding all the welds...        read full caption After grinding all the welds down, go back through and find any that need a little more fill, such as the one shown here.

After all the plugs are filled...        read full caption After all the plugs are filled flush, reapply the seam sealer.

Time Machines prefers 3M&8217s...        read full caption Time Machines prefers 3M’s Fast n&8217 Firm, available from most automotive paint supply houses.

After the spare tire mount...        read full caption After the spare tire mount was removed from the car, it was decided not to reuse it due to the exceedingly sloppy factory weld. To reinstall it, just place it according to your diagrams and measurements you took before you started and weld it in. On this original, you can see where it was spot-welded on one side, but a solid bead was laid down on the other. Sort of.

Except for the final weld...        read full caption Except for the final weld down the center to join the two halves, the trunk floor finished. Time Machines tack welded the halves of the floors together, and will finish the solid weld later when they do the body work on the car. Because it’s a concours car, this seam is going be finished as if it were an exterior panel--body filler, skim coats, and all. However, if you’re doing a driver, just weld in 2-inch increments and allow the welds to cool before starting the next one to minimize warpage. Viewed from the top and underneath, it looks like a factory installation with the spot welds.

Installing body and patch panels can be an intimidating process for the novice, even with the high-quality reproduction panels available today. As a result, most enthusiasts leave the job to experienced shops who do this kind of work all the time. We followed along with Time Machines in Hudson, Florida, as they installed a complete trunk floor in a 1970 Superbird. What we discovered is that this is a job that almost anyone with a welder can do, regardless of experience. Since trunk floors are common rust areas, this is a great confidence builder for the novice to attack before moving on to something bigger. While Time Machines is performing a concours resto on this ’Bird, the process is the same for anyone doing a driver in their garage. We ordered a complete B-Body trunk floor from The Paddock in Largo, Florida, and followed along as Phil Somers and the guys from Time Machines removed the old floor and installed the new.

Aside from a welder, the only tools required are tin snips to trim the new panel to fit, a spot weld cutter and drill, a grinder, and a saber saw to remove the old floor cleanly, though Time Machines employed a plasma cutter. This is also a good time to mention a trick we learned that may aid you when buying your next project car: If you're checking out a car with no carpet or trunk mat, and it's sitting in a poorly-lit garage, throw a trouble light under the car and look at the floor--you may be surprised at the amount of small holes that show up, but otherwise weren't visible before. Finally, though this seems obvious, make sure that the gas tank and filler neck are removed from the car before you do anything. This is a job that can easily be tackled over the course of a weekend by a beginner, and completed with professional results.