How to Replace a Trunk Floor

by George Nenadovich


The first item to remove is the gas tank. This will require you to completely drain the tank. No need to handle extra weight when gas can easily be emptied. The two straps shown here hold the tank to the gas tank braces which are welded to the bottom of the trunk floor. The rear screws are 3/8" hex head. The front bolts are 9/16" hex head. It is a good idea to spray the bolt threads with PB Blaster to aid with removal.

Here is the inside of the trunk with the lower arrow showing the opening for the gas tank sending unit wire. The upper arrow shows the connector for the sending unit wire.

Here is the gas tank with the left arrow showing the ground wire (notice end of wire is missing due to corrosion). The right arrow shows brown sending unit wire. Since the tank is out....good time to check the sending unit, inspect inside the tank for dirt and paint the tank. This one is in excellent condition...despite some minor flash rust on the top.

Here is a show of the trunk floor which "appears" to be in ok condition but the arrow shows sunlight passing through from the bottom............bad fiberglass work by previous repair person.

Here is the driver's side tank support. Due to massive corrosion....lower arrow indicates where the capture nut broke loose from the factory snap-clip. When this happens use a wrench to grab the 9/16" hex nut and then remove the gas tank bolt. Upper arrow is the tank ground strap with end still in way to remove this due to corrosion.

Here is the passenger side gas tank very good condition for being 37+ years old.

Here is the driver's side gas tank support....heavy corrosion.

Here is the passenger side support with gas tank capture nut still in place. Small bracket above it holds the 70 gas tank vent in place.

Another pic showing driver's side corrosion and sunlight coming through the floor.

Here is a bottom side view where light was passing through when viewed from above.

Someone tried to fix this floor using fiberglass when the proper way to fix the floor is to replace with new metal. Someone used cardboard as a form to keep the fiberglass resin from falling through the large rusted-out areas.

Here are some basic tools needed for trunk floor pan removal. I like to use the air shears to remove most of the metal quickly. You can also use a plasma cutter but those are expensive when compared to the air shears. The drill is used to drill out the factory spot welds. I like to use the 5/16" "bullet tip" design available from Home Depot. The Bosch 4" grinder will come in use for the spot weld removal and new spot welds. The 90 degree die grinder works great in tight places such as the body supports and tank supports where the air shears will not work.

Since I have the body off the frame.....I like to place towels over the trunk lip/edge to provide a comfortable work surface since I will be spending many hours leaning over the edge.

Here is the trunk floor after I removed all the fiberglass....about 1/4" of it over the entire floor surface. Now it is clear the amount of trunk floor rust. Good thing about this rust on the driver's side is easy removal of trunk floor since all metal is basically rusted away.

Here is the new one-piece trunk from National Parts Depot Part C-12981-110A. This is from their Chevelle catalog. Cost is $90 and this has worked well for me on many cars. This is the wide version. The narrow version is only slightly narrower. If the entire trunk floor is bad, you will need to get the three piece set.

Here is the trunk floor after my first rough cut. Notice badly shaped need to be clean here...just need to remove most of the bad material and inspect gas tank and body supports. Notice left gas tank support is was badly rusted.

Here is the driver's gas tank support.....badly rusted. These are also available from National Parts Depot, C-12981-125B, for $30 each. See pic below.

Another pic of the gas tank support.

Here is the tank support with gas tank ground screw still attached. Notice there are 6 welds for this end. Upper arrow indicates where one factory spot weld was not good and easily pulled loosed from the trunk floor.

New gas tank support from NPD....excellent reproduction.


Here is the one-piece just placed in trunk for measurements. This easily slides through the trunk opening. Fit is excellent. Now is the time to take a Super Sharpie marker or similar and outline the new trunk pan on the exisiting metal.

Here is the spare tire hold down. New pans do not come with this so use the 5/16" drill to drill out all 6 welds.

Here is the new pan...notice no spare trunk hold down. Never throw away old metal until the job is complete because you never know what items you may need.

Here is the passenger side gas tank support. Arrows indicate the factory spot welds drilled out of pan in order to remove the rusty metal...some of the metal wound up on the ground below. Try not to drill through the supports.

Same support with all spot welds ground flush using the 4" grinder.

Here is the final cut. Notice black line above it. This is the edge of the new panel.

Upper arrows indicate outside egdges of driver's side tank support. This insures the new tank support is placed in exactly the same location as the original. The lower arrows indicate location of factory spot welds for support.

I like to use this product, phosphoric acid, from Home Depot to neutralize all rust. This works well. Spray it on with a garden spray or old paint gun. Let it work overnight. Use a brass brush to remove any chalky residue and then wipe down with lacquer thinner.

This is a good product to spray on all areas to be welded and those that need additional corrosion protection such as gas tank and body supports.

Here is the rear body mount capture nut. Now is the time to use a 7/16-14 tap to clean the threads and repair the capture cage if needed.


Here is the hole punch/panel flanger and Cleco pliers with pins. This set-up works

great for install all kinds of sheetmetal.


I punch holes in the new metal every 2-3 inches and then use a 3/16" drill bit to drill the corresponding holes in the exisiting sheetmetal. This ensures a nice, clean and tight fit. You can buy the pliers and pins from Racer's Parts Wholesale and the punch/flanger from Harbor Freight

Picture showing spot welds to hold trunk pan to new driver's gas tank support. Repeat for the passenger side.

Here is the front side of the pan. All these holes will be drilled with a 3/16" bit and then install Cleco pins.

Here is an overhead view of the entire new pan.

Here is a bottom view showing nice, tight fit with new gas tank support.

Here is the pan after all the spot welds are done and ground smooth. I apply a light coat of phosphoric acid to prevent any future corrosion.


I like to use this product available from Home Depot to seal all the new seams. This has worked extremely well to replace the original white seam brush-on sealer. This is black so it blends very well....same item I use for all the cowl seams. Use a small body filler squeegee to apply a nice smooth coat. This will make the trunk pan installation hardly noticeable.


Depending on how much floor rust and how much new metal is needed this job can take from 8-16 hours from start to finish.