68-72 Floor Pan Installation
By John White
4-6-2007
There are several things to be aware of when installing a single piece floor
pan into your El Camino. First, it does not fit into the doors or through the
back window. It might fit through the front window but only if you remove
the dash and steering column. The advantage of buying the single piece
floor pan is you decide the best place for the seam. I chose to cut it from
side to side between the seat mounting studs. I considered cutting down the
middle, but I thought sealing the seam over the tranny would be too
difficult. Another option is to take the body off the frame but that's another
story all together.
You'll
obviously want to remove the rusty floor. My floor was previously repaired
but done very poorly and they left the old rusted floor installed.
Consequently, the rust continued to spread until it compromised the welds
holding the repairs.
I suggest cutting at a few inches into good metal. For me, this meant
removing the entire floor pan, the storage box behind the cab and portions
of the kickup panels. There are 2 cross braces under the floor pan and
another on the back edge. Be careful not to cut through these unless you
bought the floor with the integral cross braces (which I think only has the
two braces in the middle). Figure 1 shows what about 3 or 4 hours with a
plasma cutter will do to an El Camino floor. Notice I cut a little more than
an inch inside the original floor to rocker panel seam.
Next I stripped the paint from where I expected the new pan and panels to
fit, prepped the metal with acid and used POR-15 over all the surfaces. I
figured that burning through the POR-15 and dealing with contamination in
the welds is easier than dealing with rust in the areas where the metal
overlaps and where seam seal may not be easily applied. Others have
different ideas of how to prevent ongoing rusting. I'll just recommend using
your best judgment knowing that there will be some overlapped areas that
might trap moisture.
I cut the kick up panels to fit, allowing a couple of inches of overlap to the
existing. The kick up panels have a flange on the outside. On my car, the
right hand flange was about ¾" short of the metal behind the kick panel. I
cut the flange off and welded to the flange I left remaining (above I asked
you to note where I cut the floor). On the drivers side, the panel fit
perfectly, and I welded the top of the flange to the metal behind the kick
panel.
I installed the
rear floor pan (the one that fits behind the cab but under the front part of the
bed) first. The front of this rests on a cross brace that also supports the back
of the original cab floor. Figure 2 shows the back of the cab. Notice the
downward brace on the passenger side. This was attached to the original
cab floor pan where the pan ends up just in time to bend over the cross
brace. If you have the original floor, you'll see that this bracket comes
forward of the back panel about 1½ inches.
I point this out because I was surprised to learn my floor pan was about 3 or
4 inches shorter than the original. From my measurements, I found the
dimensions from the back of kickup panels to the front and middle cross
member seem correct. However, the distance of the pan from the second to
the last cross member is short.
There are a
number of ways to compensate. If you want as close to original as possible,
you could splice in some rear floor panels locating the new panels correctly
to the brace or you could cut the floor behind the seat and add a 3 inches
strip to the pan. I opted for adding a 1½ X 3 inch channel over the rear
support. I should mention that I did this to reinforce that part of the body
because I planned to cut the bottom of the back cab panel away so I had
access to the storage box from the cab. Figure 3 shows my configuration.
Once I got the floor pan in place I secured it with about 25 or 30 sheet metal
screws to what was left of the existing floor and to the bottom flange on the
kickup panels. After I was satisfied with the placement, I wire brushed the
areas I was going to weld and then welded it in place.
By the way, even though I removed the paint where I could see it, there was
still enough burnt paint to give me a horse voice and sort throat. I quickly
got a fan to suck the fumes from the car.
Some might criticize my full seam welds instead of stitch welds. I'm OK
with that. However, I'll recommend you use your best judgment keeping in
mind that the floor becomes a shear panel when the frame starts twisting.
The frame might twist because it's old or because you are using smaller
profile tires with tighter suspension or you've put in a 550HP mill with 4.54
gears and a posi. I figure my time is cheap as is wire and Argon/CO2 mix.
Again I say, be sure to think about how you want to manage the frame
energy, especially if you're making performance modifications.
To attach the
floor to the cross brace, I crawled under the car with a 0.09" drill. I drilled
through both the front and back cross brace flanges and through the floor
pan where the cross brace bent forward or back. From the top, I opened the
holes in the floor pan to 0.19 and used screws to draw the floor to the cross
braces. Afterward I drilled ¼" holes between the screws in straight lines
knowing the screws represented the cross brace bends. I opened the ¼"
holes to ½" in the floor pan (not the cross brace flanges) and rosette welded
the pan to the cross member from the top. You can see this in Figure 4.
There is still some unfinished business as shown in Figure 3. I will cut the
vertical support running front to back and install a web across the front that
picks up this support and ties the existing back panel to the new channel.
Each side will receive a similar treatment. These webs will provide shear
support from the floor to the original panel. By tying it into the vertical
support, I'll support up and down forces and distribute them over a larger
area. It also will keep things in the back from sliding side to side.
The final step is to apply suitable rust protection and seam sealing. For
areas that will not be painted, PL polyurethane, which can be bought at the
local hardware store, can be used; it is softer and therefore easier to apply…
especially to that seam that is between the rocker panel and the frame.
Undercoating seems to stick to this product but it is too soft to hold paint.