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Old 04-02-2021, 03:24 PM
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TheBandit TheBandit is offline
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Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,654
Tunnel Fabrication

I've always thought of my car as a vehicle (pun?) for lifelong learning. I take on projects to challenge my knowledge, skills, and experience. That's why I often do things the "hard way" - the resulting personal growth is always a payoff, even if the results on the car aren't perfect. Yes it can be frustrating - failure is frustrating - but it has always been worth it!* Swapping this big transmission into the car was another great opportunity to learn and stretch myself, especially with the need to build a transmission tunnel.

To start the tunnel replacement project, I cut and bent a 1" wide piece of 20awg sheet metal to serve as a profile template. I wanted the resulting tunnel shape to be flat at the top with a radius along the edge, so I went through my collection of random pieces of pipe and wood until I found a piece of a closet dowel which made a bend profile I liked. I could use the same pieces of dowel later to form the tunnel. I made several versions of this profile with different dimensions before I decided on this particular one. To make sure it sat level and centered in the tunnel, I marked the centerline, equal distance bend lines, and equal distance cut/alignment lines so all I had to do was line things up in tunnel opening to get it centered and level. To get the right height, I started out with a longer-than-needed profile, laid a long straight ruler from the shifter to the profile, and moved it up and down until I liked it, marked an alignment line on one side, then carefully measured and reproduced the alignment line on the other side. I used basic spring clamps to position it as I made adjustments, then once I was happy I drilled a hole through each side and installed a Cleco clamp. This was my first ever project using Clecos and they are absolutely awesome!

Next I needed a template to get the right shape for my first piece of sheet metal. It tried taping some light poster board over the opening, but it did not want to comform to the shape very well, so I ultimately used a bunch of painters tape instead. I laid strips between my profile and the original tunnel, eventually building up the needed shape.

I quickly found there was no way I could fit a marker inside the tunnel to mark out an accurate edge for my template. That's when a little brainstorming paid off. I grabbed my Xacto knife and used that to cut against the edge of the tunnel, creating a perfect template of the right shape!

I carefully transferred my masking tape template onto a piece of poster board so the edges would not end up sticking together. Then I traced that template onto a piece of sheet metal. It's worth noting that before I even cut the masking tape out of the car, I made match marks at the center of my profile template and the car so could line things up later - I transferred those alignment lines to the sheet metal as well. Finally I drew out flanges that would later serve to overlap the existing tunnel for future welding.

I cut this piece out using a combination of electric shears for most of it and hand shears for a few detail areas. Then I slowly, incrementally bend the piece by hand from the center out until I had a decent fit in the car. This involved going back and forth to my closet dowel and carefully connecting the radiuses of my profile back to the corners where the piece meets up with the original tunnel/firewall area. I did this incrementally and it involved dozens of trips to the car to check fitment, then back to the workbench where I hand belt the piece over various random objects.

The piece was starting to look good, so it was time to bring out one of my favorite new tools:

This is an Eastwood 19" bead roller. I have been wanting a bead roller for more than 15 years, but I could never justify the expense. This project was just what I needed and I am SO GLAD I picked this thing up. I modified the bead roller by attaching my old Grant steering wheel using a 1" set-screw shaft collar welded to the back of the wheel. Here is a quick video review for anyone interested:

For this first piece I used the bead roller three different ways:
1) I installed the polyurethane lower die with an offset/flange upper die and "tipped" the front edge of the piece to make the angled flange that follows the front of the tunnel. This was was a little tough because adding this flange caused the material to straighten out, so I had to reform it a few times until it stretched enough to keep the* both the curve of the tunnel and the flange I needed for attachment.
2) With the offset dies, I added flanges along the bottom left/right edges of the piece. This was very straight forward, but I should note I also followed up with the polyurethane lower die so I could tip an angle into the flanges.
3) With the smallest beading die, I added partial beads on either side that meet up with the original tunnel beads from the factory.

Here is how the pieces turned out. I was really stoked!

Now it was time to create the rear profile to establish the shape of the main section of the tunnel. Once again I cut a 1" wide strip of sheet metal, measured center line and bend locations, and adjusted the height using a long ruler until I found just the right shape and position. I narrowed the profile of my bent piece about the same amount as the narrowing of the tunnel open, so when viewed from the top the entire tunnel would taper toward the rear.

For this template I decided to try poster board again. To be honest this did not work the best. The poster board I was using was just a bit too thick to establish the bend at the top edge. You can see in the photos it's a bit deformed, which later meant the metal wasn't a perfect match, however because I used overlapping pieces it did not make any difference to the final fitment.

Here is where thoughtful planning and patience came in. I've learned over many projects sometimes I have to remind myself to slow down and take the time to think a project through. When doing layout, it's imperative to get your mind in the right place and even step away and come back to check over or adjust your work. Below is the layout I put together for making this section of the transmission on a sheet of 20awg steel. You can get a sense of how much thought I put into laying out the bends, cuts, flanges, and beading paths. I labeled areas that would become bends, bends or flanges and I also cross hatched the areas I intended to cut out to avoid mistakes. This took a lot of time with a few good rulers. I can't stress enough how important a good layout is and you'll see how that translated into the finished product further in this post

Here's a video screengrab of cutting out this piece. I have to say, electric shears are AWESOME. This was my first project using a set and it's so so much better than using a jigsaw or hand shears. The metal does not deform at all and it cuts quickly. It's also very easy to line the edges of the shears up to cut lines for a very accurate cut. Electric sheers, step bits, Clecos, punches, and bead rollers are now my favorite sheet metal tools!

Once the piece was cut out, I used offset dies in my bead roller to make panel reliefs. All I had to do was carefully follow my layout lines. I did this in a single pass on the bead roller and most of my lines met up well. I could point out some of the faults, but most people would never notice. The best thing about these reliefs is they did not distort the panel whatsoever.

Next it was time to form the radius edges. The right tool for this would be some kind of a sheet metal brake. A magnetic brake would be my choice if I had unlimited funds, but I learned a long time ago you can do a lot with just your hands and a few random objects & clamps. Here I am using closet dowel as my bend radius, a 2x4 to keep the dowel reasonably held down, a pair of clamps to hold it to the workbench, and my hand/knee to bend the sheet metal as I supported the dowel with my other hand. I worked along the edge back and forth and checked the bend angle with a simple protractor until I had a consistent bend from side to side.

I cut a quick and dirty hole for the shifter to poke through, then ran it to the car to check fitment.

WOW! I had envisioned something like this, but seeing it in sheet metal just blew my mind. I could not believe I made this myself. Back to the bead roller to add & top flanges and a bead...

You can see my goal was to match the factory floorpan bead and carry it over the top and have a flange along the edge for overlapping & welding.

At this point I felt the fitment was close enough that I could cut out my two access areas and see what they looked like. I also began adding Clecos to "suck" the pieces together and keep things in position. Each of these cutout areas serve a purpose. The rear one is long with lots of room behind the shifter so that I can lift the transmission completely into position before sliding the transmission shaft forward through the clutch as I mate it to the engine. The front cutout makes it easy to reach my hand in to access bell housing bolts. I found both of these very helpful when R&Ring the transmissions at various stages of mockup.

With a few more Clecos, here is how the transmision tunnel was shaping up


Ongoing 70 Nova build:
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