As I’ve previously mentioned, I’m completely changing the rear 20% of the tail. The stock tail is a single pivoting piece that supports the tail lights and has an integrated “diffuser.” This approach is easy to implement, but the pivot motion interferes with the wing and exhaust and the molded diffuser is more of a parachute that anything else. Mine will have a fixed rear bumper that supports the wing, tail lights and a functional diffuser. The engine cover will hinge backwards towards the tail.
About 18 months ago I chopped the tail. Before taking a reciprocating saw to it, I spent some time thinking about how I would maintain the correct orientation once the hinge points were cut off. I welded a temporary support to the top of the rear suspension brace. It has two locating pins (borrowed from the nose) that stick through the tail to index and support it in the middle. From the underside I drilled a hole through the temporary bracket and the fiberglass - this got the X/Y coordinates perfect. I then tapped the bracket, enlarged the hole in the fiberglass and screwed the indexing pins in. By threading the indexing pins up and down I was able to get the Z axis perfect. I then added a jam nut so that it wouldn't move.
While the indexing pins locate the tail they won’t prevent it from deforming when the duck tail is removed due to a combination of the weight of the wheel arches and tension in the fiberglass which is released when the duck tail is removed. To address this, I tapped holes in the tube and installed leveling feet upside down. Since they have a ball socket I was able to get the wheel arches perfectly dialed in. I was careful about how I cut the tail so that I can use the removed piece to validate that everything is where it's supposed to be. As can be seen in the video above, the tail doesn’t deflect when the chopped section is removed.
Temporary support bar welded to top of rear suspension brace; two leveling feet and two indexing pins
Right-side indexing pin (left) and leveling foot (right)
Right-side indexing pin sticking through the fiberglass
With the tail chopped, indexed and supported, I needed to stiffen the engine cover and provide a way to mount the hinges. While the final version will achieve this via carbon fiber tubes and bonded steel plates, I have a lot to figure out before then. So, I welded some right-angle to a 3/4" square steel tube and bolted it to the back edge of the engine cover.
I’ve also started finalizing the tail subframe which is made of 1” OD 0.120” wall 4130 tube. It supports the wing, transaxle oil cooler, rear bumper, tail lights, titanium exhaust, and engine cover.
Tail subframe with temporary wing and hinge mounts welded to clamping two-piece shaft collars
Rather than design and fabricate a hinge I looked for an aftermarket billet one. The majority that I found are for 60s and 70s muscle cars and I settled on 60’s era Mustang trunk hinge. I didn’t want to splurge on the billet version until I had proved things out, so I bought a stamped steel one on eBay. I’m glad that I did because I had to hack their mounting plates to get them to fit around the temporary tube bolted to the back of the engine cover. The hinges have vertical slots to facilitate adjustment so I fabricated some temporary plates with horizontal slots. I didn’t want to tack weld them to the tail subframe so I purchased several clamping two-piece shaft collars with a 1” ID and welded the plates to them. This provides a lot of adjustability and is easy to remove when I fabricate the final version.
I took the same shaft collar and slotted bracket approach to temporarily mount the wing. Once the hinge was mounted I removed the locating the pins and opened the engine cover. It was as smooth as I hoped, but it’s a two-person job because the engine cover has a lot of flex. Once I stiffen it and add air springs it will hopefully be a one-handed, OEM-like exercise.
Engine cover hinged open. The red line indicates where the fiberglass will be sectioned to clear the wheels. That part will be fixed to the rear bumper.
I need to make a big decision on which tail light I’m going to use so that I can begin to finalize the body mods, exhaust and diffuser.