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How to Install a Trunk Floor in a 1957 Chevrolet Bel Air

No Junk In The Trunk - We install a mini-tub trunk floor in a '57 hardtop for a solid trunk and more room for tire.

Patrick Hill Apr 23, 2014
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When we started working on this '57 hardtop in the 2013 issue of Chevy Classics, it had been sitting for almost 20 years, as its owner tried to figure out a course of action for fixing its solid but hacked up floor and firewall from a previous owner's butchering. Thanks to the ever-growing Tri-Five Chevy parts market and Classic Industries, instead of a complicated series of patches involving metal fabrication, we were able to install a brand-new, one-piece floor and firewall, solving most of this car's ills. That just left the trunk floor.

The plans for this '57 involve bolting it to an aftermarket chassis of some sort, stuffing in the baddest LS motor the owner can build, and turning the hardtop into a monster Pro Touring machine. To achieve this, we knew at least a 315-width tire would have to be installed out back. This meant mini-tubbing. So, the fairly solid trunk floor was gonna need to be modified, along with repaired, because of rust in the floor and the tailpanel area. Once again, Classic Industries provided the perfect answer: its deep-well trunk floor, which comes pre-narrowed for a mini-tub installation.

Even though it took a little more work than the passenger floor, the trunk unit went in fairly easily, and the fit was perfect. In this story, we're going to cover getting the floor in place and ready, so in the next installment we can measure and cut for the mini-tubs, weld them in, weld the floor in place, and finish up by installing the tailpanel. Once done, our '57's body will be as good as new—with all-new metal from the firewall to the trunk—and ready for us to begin the next phase of the project.

Classic Industries Parts List
Tailpanel – TF400652
Deep Tub Trunk Floor – TF400952

1957 Chevrolet Bel Air Trunk 2/23

1 Here's what we started with. Overall, our trunk floor wasn't in bad shape, but the metal on the passenger side was a bit thin with a couple of pinholes, and back by the tailpanel and tail brace, there was some rust.

1957 Chevrolet Bel Air Stock Wheel 3/23

2 One of the reasons we're doing this install is to make room for a mini-tub modification, so we'll be able to stuff at least a 315-size tire in the back. With the stock wheeltubs, this is impossible.

1957 Chevrolet Bel Air Remove Old 4/23

3 The first step in removing the floor was using a MAP gas torch to melt away all the old paint, Bondo, and lead on the seam between the tailpanel and taillight-area metal.

1957 Chevrolet Bel Air Tailpanel 5/23

4 Once we started digging, we realized the car's original tailpanel was badly rusted out, along with the tailpanel brace underneath it. This is a normal area for rust on Tri-Five bodies, as it's a collection point for water running down the back of the car.

1957 Chevrolet Bel Air Cut 6/23

5 Using a Sawzall, we cut inside the tailpanel seams to remove the panel. We'll go back later and drill out the spot welds holding the end pieces to the rest of the body and prep them for a new tailpanel install.

1957 Chevrolet Bel Air Tailpanel Brace 7/23

6 Under the tailpanel, we found serious rust damage to the tailpanel brace. Fortunately, the new trunk floor comes with the brace already installed. If all you need is the brace, Classic Industries sells it separately.

1957 Chevrolet Bel Air Cut Floor 8/23

7 To make things easier, we started to use a Sawzall to cut out sections of the floor.

1957 Chevrolet Bel Air Plasma Cut Trunk 9/23

8 After a little bit of fighting to get the Sawzall into certain angles, we pitched that and grabbed our plasma cutter and used it to carve up our old trunk floor. The plasma cutter made quick work of it.

1957 Chevrolet Bel Air Trunk Floor 10/23

9 After about 30 minutes of cut-ting, here's where we stood. We stopped short of the factory shock mounts because we'd need to do some more delicate work to get that section removed.

1957 Chevrolet Bel Air Grind Old 11/23

10 Because of 57 years of corrosion, trying to find the factory spot welds to drill out on the old floor would've been nigh impossible and extremely time consuming. To get the rest of the old floor removed where it was welded to the inner quarters, we started by using a grinder to knock off some of the edges left, and split the metal in a few places.

1957 Chevrolet Bel Air Driver Side Corner 12/23

11 We found some rust in the driver side corner down low. We'll clean and patch up this area with some metal before we install the floor. Be prepared for this on your car.

1957 Chevrolet Bel Air Remove Trunk Floor From 13/23

12 After using the grinder, we grabbed a heavy hammer and a large flat-bladed screwdriver, and split the remnants of the old trunk floor away from the quarters. It took some time and patience, but was still faster than hunting down all the factory spot welds.

1957 Chevrolet Bel Air Clean 14/23

13 After all the old metal was removed, we went back with a clean up or "flap wheel" to dress the flanges on the inner quarter where we'd be welding the new floor in so we'd have good, clean welds.

1957 Chevrolet Bel Air Remove Back Seat 15/23

14 If this were a normal trunk floor install, we wouldn't have to remove the back seat brace. But since we're going to mini-tub our car, it has to come out. On this one we used our Eastwood skip-proof spot-weld driller (PN 11276) to drill out all the factory spot welds.

1957 Chevrolet Bel Air Back Seat Brace 16/23

15 With all the spot welds drilled, all it took was some light prying and the back seat brace popped out. In the next part of our story, we'll cover the modifications to the back seat brace that are necessary to go along with the mini-tub install.

1957 Chevrolet Bel Air Flatten Out 17/23

16 Before slipping in the new trunk floor, we went back with a body hammer and dolly to flatten out the flanges on the inner quarter.

Classic Industries Deep Tub Trunk 18/23

17 Here's our new Classic Industries Deep Tub Trunk Floor, PN TF400952. It comes with the tailpanel brace already installed and with the factory spare tire well deleted. The area where the wheelwell cutouts are has already been narrowed, saving the installer a lot of time.

1957 Chevrolet Bel Air Install Trunk 19/23

18 AntiVenom Performance's Greg Lovell is the Herculean type, and he muscled the floor into place by himself. For most, it'll be good to have a second set of hands ready to help you get the floor in place.

1957 Chevrolet Bel Air Set Trunk 20/23

19 Supported by a couple of jackstands, we had the floor set in place to check fitment, which was perfect. It lined up beautifully with the Classic Industries passenger floor we installed back in the 2013 issue of Chevy Classics. From here, we clamped it in place.

1957 Chevrolet Bel Air Wheelwell 21/23

20 With the new, narrower floor and the stock wheelwells still in place, you can see how much width is allowed for the mini-tub modification.

1957 Chevrolet Bel Air Trunk Floor 22/23

21 From the inside, here's how it looks. Part of the mini-tub job will involve modifying the rear of the passenger floor, which we'll cover in the next issue. But in the picture you can see how it fits like a glove with the passenger floor.

1957 Chevrolet Bel Air Trunk Floor 23/23

22 And there you have it. We only have the floor clamped in right now, since it will have to come back out for installing the mini-tub kit (also from Classic Industries), but in the next installment we'll cover welding in the floor, mini-tubs, and the new tailpanel. After that, our '57 will be ready to have what's left of its original Matador Red paint blasted away and the body prepped for whichever chassis we decide to mount underneath it.


Classic Industries
Huntington Beach, CA 92648
Seffner, FL 33584
Eastwood Company
Pottstown, PA 19464



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