Rear Guards & Tail Panel

With the wheelwells finally in place I can start to prepare all the fiddly corners & edged on both the body shell and the new quarter panels to enable them to fit together correctly.

Here is a shot of the rear end after a dummy assembly to see how all the new pieces come together - almost gives enough incentive to continue!
And no, that old couch next to the car is not my bed after the wife kicked me out for spending so much time on the car.....

I've used the method shown in the Mustang Monthly "How To" section under the heading "Quarter Panel Repairs" as my guide on how to do this. Basically, I am spot/plug welding the rear quarters along the front, rear & lower edges - while butt welding the top edge all the way from front to back (back to where the new quarter panel cuts in and joins the trunk drip rail).

However, as both aftermarket quarter panels are not a perfect fit, there is a HEAP of work involved in making sure everything lines up properly from a measurement and aesthetic perspective. This is a warning not to expect a good fit initially!
While the chassis construction was a "build to specification" job by constructing everything according the original engineering drawings, positioning the rear panels is more of an art. There are simply no dimensional measurements I can find that state exactly where (for example) the top outside edge of the rear quarter should be, how high the top edge of the tail panel should be, etc!
A BIG assumption I've made to guide me to where the rear quarter & tail panels should be (an assumption I had to make actually) is that the original trunk lid is very straight and undamaged. If this is true then I figure that if I re-fit the trunk lid to the body shell as perfectly as possible along its upper front edge - then I will have a good guide for positioning the rear quarters to give me the correct panel gaps along the trunk sides (as well as a guide for panel contour, height, length, etc). This is where many many many trail assemblies come in handy as well as an eye for what "looks right".
Here are some shots of various "dummy assemblies" to check panel fit. I had to reshape several edges to make them parallel with the trunk lid. Note that I have temporarily cut away some of my "space frame" and mounted the rear-end (nice & level) on blocks to refit the trunk lid.

I had to "unpick" spot-welds on (both) the rear quarters and reapply them properly to get the panel contours to match the profile of the top edge of the rear quarter extensions.
Notice the major panel gap mismatch between the right-hand trunk edge and the combo' of the rear quarter panel and extension. Lots of work needed to get this gap right!

I also have a "fallback check" in place as I have once again set the bodyshell perfectly level (ie, it is rigidly mounted to the ground at the leaf-spring mounts and wont spin on the rotisserie). This means that no matter what I do on one quarter panel, I can compare its height and width with the other quarter panel to make sure they both end up the same. The following steps need to be done when replacing rear quarters......

• Repair any rusted supporting panels that the new quarters attach to - to get the foundation right. I fabricated various custom patches for this. I found that the lower door-jams (just above the sills) had small areas that needed patching on both sides. Once patched, the internal faces of exposed metal were painted with Rust Bullet (while the external faces will of course get protected by body paint).


• Next I prepare any plug/spot-welding surfaces by removing the existing paint primer and replacing it with U-Pol weld-thru copper primer.


• Next I heated & removed the lead filler that was applied by Ford at the join of the trunk/roof/rear quarters. This is followed by some panel beating to straighten up any edges where I drilled out old spot welds.


• Next I refit the trunk lid and set the gaps as close to 3/16" as possible ensuring the trunk-lid height was flush with its adjoining front panel (the panel situated between the trunk and the bottom edge of the rear window).


• Now I could trial-fit the quarters to check/fix panel fit and required panel gaps.


• I also replaced the trunk "drop offs" as these were cheap to buy, easy to install and provided a perfect new surface to plug/spot weld the lower edges of the new quarters to.


• For better long-term rust protection I removed the temporary primer from the inside surface of the rear quarters along the lower edges and up over the wheel arch - and coated the bare metal with Rust Bullet.


• And lastly, I used my trusty measuring tape to make sure (first the chassis and then) both quarters were the same height (above level ground), width (for panel gap and from vehicle centre) & depth (flush with the rear face of the quarter extensions).

Below you can see the inside lower surfaces of the quarters better protected with Rust Bullet.

Notice (below) also that I deviated from OEM spec's along the bottom edge of the tail panel by grafting in some 2mm wall thickness 2" x 2" box tube. This tube solidly ties the rear frame rail together and provides a nice flat surface for spot welding my new tail panel to. The primary reason for the box tube at the rear though was to give the new large capacity stainless steel petrol tank a solid mounting point. The stainless tank is straight out of my old Ute and has a recess in it for fitting the battery (a recess for the battery just like current BMW sedans). This makes the tank/battery combo quite heavy and in need of solid mounting points. This design also keeps all significant rear weight items as low as possible to the ground.

Once the quarters were prepared I tack welded the top front edge as seen below. This makes sure the whole panel doesn't lift at this crucial spot (its right where the door closes and so the panels need to line up). I re-hung the doors as well - as a guide to make sure everything lined up and was a flush fit. In this photo you can see the initial tack welds that i put every 2 or 3" along the top edge of the new quarters in preparation for the final butt-weld. Thankfully, the new panel contour along the top edge was quite close to the original metal profile as can be seen here if you enlarge the photo. And yes, a final patch will need to put into the pillar!
Here is a shot from the rear showing the plug & tack welds. I'm leaving the surrounding old paint and body-filler in place for now to stop surface rust....

And shown below is the other quarter after fully butt-welding the top edge and then smoothed off with the grinder (using a sanding disk). Everything lines up nicely!
With the quarters in place it was time for the tail panel and associated trunk drain channels on the outer edges. I couldn't get my hands on the trunk drain channel corners for a Fastback so I used both the original pieces I cut out and a set of new coupe trunk "drain corners" to fashion new ones - just another few hours of custom fabrication... ho hum.
One thing I did find was that my trunk lid was slightly warped by about 5mm from one rear corner to the other, and, that the final shape of the trunk itself (when shut) is affected by the existence of the rubber seal or not. I had to re-attach segments of the rubber seal to get my final contours right. Lesson - don't remove the rubber seal if going down the path that I did.

Other than that, I had to adjust the section of the rear quarters (where the extensions bolt on) to get the tail panel to sit parallel with the ground. One side was "formed" higher than the other - which is what you can expect with these aftermarket items. As the tail panel was a simple flat sheet of steel (and nice and "square" when measured), it was clear that the back of the rear quarters were the problem.

And here is the result (but not a good exposure I must admit). I've temporarily sprayed any exposed metal with black epoxy primer to prevent rust. Mmmm, maybe a matt-black Fastback would look ok!?

Floor & Rear Wheel Wells

With the full chassis now installed I can cut back on the existing space-frame to free up room to install the floor. I can also now drop the front of the rotisserie back down on the garage floor - as I had chocked the front up on blocks to make the whole shell perfectly level and rigid (for accurate installation of the chassis). See the shot below of the various blocks used to lift the front of the car to a "factory level" position - just prior to chassis installation.

I used factory standard '65 Mustang chassis spec's I found on the Internet to get these measurements right. Something interesting I found with this car was that one side of the roofline (measured at the highest point of the driprail) was about three-quarters of an inch higher than the other side - even when all other frame and sill measurements down to the floor where the same (factory tolerances for 1966 maybe?)! This really surprised me as you just couldn't tell one side was higher than the other when looking at the car (looking at it either before or after dismantling). So I pulled the high-side of the roof down and made sure I corrected all critical body and frame measurements to within about +/- 1 millimeter of factory spec's.

But before the floor actually goes back in and makes it harder to access the whole body shell, I cut out the old rusted front frame extensions, repaired the areas on the front frame where the extensions attached and welded in the new extensions. Here is a sequence of shots showing the extensions being restored.....

Notice just how many spot welds are done at the factory to hold these extensions on! The shot immediately below shows the extension "stubs" that remained after cutting out the rusty floor - flared open by my cold-chisel after drilling out the spot welds and "enticed" them off.

Now notice how much rust protection was done in this area (none!). I cut out the rusty portions of the frames and replaced the cut-outs with new metal.

Because the frame-extensions are just a piece of stamped (channel shape) steel and are pushed up as a flush fit under the front frames, moisture gets trapped between the two surfaces around each spot weld. So I've painted the bottom surface of the front frame and the inner surface of the extension with "Rust Bullet". Then I pre-drilled the extensions for the new spot welds, trial-fitted them back on the frame and used a permanent marker to pinpoint where each hole is positioned on the front frame. I then ground away the coating of Rust Bullet at these marks to ensure i had clean metal to perform the spot weld (actually its a Mig weld that simulates a spot-weld by filling up the drill hole in the outer metal sheet). But before mig welding, I sprayed U-POL copper "weld-thru" primer onto each ground-back "spot". I don't think I can do any more to stop rust! The only risk I see is that there is Zinc (in the Rust Bullet paint), Copper (in the U-POL) and Iron in the steel frame - maybe electrolysis can start?..... But surely it's still better than bare metal as found from the factory! Here are the repaired front frames.

And now the new extensions with the inside surface protected with primer (after drilling the weld holes).

And here is some detail of the finished job. Very strong indeed.

As for the rear wheelwells, I used sheets of cardboard to fashion templates for the 3 pieces used on each side (inner & outer walls as well as the wide strip that forms the "roof"). I was anticipating this was going to be a real pain but it was pretty straight-forward. I first created the inner wall template and used the "spine" that remained from the original wheelwell halves as my top contour and the rear frame-rail as my bottom contour - see picture below (sorry about the background glare).

I used the outer guard as my guide to fashion the outer walls and then cut out all the templates. I allowed an extra half-inch or so on each edge in case of error...

After the inner wall was tack-welded in place I once again trial fit the rear guard to fashion the roof section. As I want and original look for the car (no flared guards) the trick here is to give about only half an inch clearance from the outer edge of the roof section to where it would touch the inner surface of the rear guard. This was easy enough to do in iterations as I simply held a permanent marker pen flat against the inner skin of the rear guard and ran it along the edge of the cardboard template. After a few goes of trimming the cardboard back along the marker pen line, the tip of the marker pen no longer touched the edge of the cardboard anywhere when rolled along inside the panel - so job done!

Next thing to do is cut the zinc-coated steel sheet as per the cardboard template and weld it in place. Looks ok in this shot below! I should mention that I took the liberty of moving the diff rebound stops from the outside (wheelwell side) of the rear frame-rail to the inner side. I also positioned the inner wall of the wheelwell inwards as far as possible - so the rear, inner edge of the wheelwell is right up flush against the vertical face of the rear frame rail. I got another inch of width in the wheelwells by doing this - nice (almost tubbed!).

Notice below how the top edge of the inner wall warps once you've welded the (curved) bottom edge. This all straightens up though as you weld the top section on.

Now just a detail shot of the welds. The Mig does a great job as long as the zinc coating is ground back. There are no pin-holes evident at all. All these weld lines will be rust-proofed of course.

I used the old wheelwell spine and various inside panels to secure the new wheelwells. Some exposed welds look a little ugly now, but they will clean up nicely with a grind-back and primer (plus sound deadener).

I had to be careful not to extend the new wheelwells too far into the cabin - otherwise I risked not being able to re-install my various interior trim panels. I also had to make sure I kept all mounting points for the interior trim and fold-back rear seat in their correct positions by welding various jig pieces onto the space-frame.

Once both wheelwells had their tops welded in, I re-attached the rear quarters to start the final fabrication of the tricky wheelwell outer walls. At first I cut another cardboard template to try and fabricate the outer wall and inward facing lip (that runs along the inner edge of rear guard that forms the wheel arch) as a single piece - but this proved way too hard. So I cut the lip off the outer wall and then hand-made the lip. I could then clamp the lip to the rear guard for a perfect fit and then tack weld it in place to the outer wheelwell wall before once again removing the rear guard and fully welding the outer wheelwell wall in place. Confused? If so, then hopefully the following pictures of the successful method illuminate things.....

First I tack-welded the outer wheelwell wall to the roof and cut it's lower edge back carefully so that when the rear guard is fitted, the contour of the lower edge fits neatly along the guard lip. There is less than a half-inch gap as you can see below.

Next, use the guard lip to fashion a cardboard template that is then used to cut the metal strip that will become the wheelwell "lip". This shot shows the lip being initially bent over. Hammer & dolly work cleans this up later.

Now I clamp the new lip to the inside of the guard for a perfect fit and tack weld it on. Then I refit the guard (with its included lip in perfect position) and carefully locate the whole guard as if it was being fitted itself for the final time. I then tack-weld the flange of the new lip back onto the wheelwell outer wall (tack weld from inside the wheelwell).

To finish, I grind off the tackwelds that hold the lip to the rear guard - so I can once again remove the guard. This then gives me access to completely weld the lip to the wheelwell from the outside. All that's needed to complete the job is to grind back the welds and cover any exposed raw steel (inside & out) with rust-proof paint.

None of these welds will be visible once the guard is in place so it doesn't have to be pretty. It just needs to have solid welds and have no pin-holes for rust to start.

Body Repairs - New Chassis Installation

While i'm making sure that the rear of the car has been structurally secured, I can start to measure up and weld in place the box-tube that will form the "full chassis". On a standard Mustang, the area where the rear torque-boxes get welded to the inner sills and rear frame, forms a nice hollow void. This "hollow" is right in front of the forward mounting point for the rear leaf-spring. This provides the perfect spot to insert a short piece of box-tube that will connect the rear frame-rail to my new custom length of chassis tube I am running inside the sills. Here is a diagram of where I am adding chassis material to the standard Mustang body.

The areas highlighted in red are the chassis additions (box tube). Tube dimensions are as follows: sill area and sill connection to the factory standard frame rails is 2" X 4" box-tube, sub-frame connectors are 2" X 2" tube. All tube is 2mm wall thickness. The total length of tube added is 3.0 meters for 2" X 2" and 4.8 meters for 2" X 4" tube. This adds just 18kg to the whole body - but improves its torsional rigidity out of site!

Here are some shots of the "sill chassis" being fabricated. With the body shell flipped over you can see the new rear frame rail tack-welded in place and the old inner & outer sill have been completely removed (drilled out the spot welds). As well as removing the bottom-front edge of the old rusty wheel wells....

I fabricated the inner sill out of strips cut from a separate length of 4" X 2" box tube. The gap you can see in the strips is intentional - it gives me a neat gap in the middle of the inner sill (looking from iside the cabin) for welding to the box-tube. This means the box tube is secured to the inner sill not just along its top and bottom edges (when looking from outside the car) but along the middle as well. Very strong!

The new outer sills fit nicely over my new "inner-sill & chassis rail combo", except where the outer sill "necks down" at the front of the car - see below. So I cut the lower edge off the front lower part of the chassis rail, spun it inwards and then welded it back in place. The outer sill now hides my new chassis completely. For the record, the new inner sills are 155mm in height.

Here is a shot of the rear of the sill chassis showing the stitch welding securing it to the inner sills. This is the rear section of the new chassis rails that weld to the front sping mounts (front mounts of the rear leaf springs).

Now (below) you can see the new chassis rail sitting in place with the front edge "inverted" so the outer sill will sit snugly over it. This was just one of many trial fittings.

The shot below shows the new inner sill in place on one side of the car. It is a vast improvement over the old patched-up sills I cut out. In this shot you can see the old rusty sping support & lower torque box still in place on the near side of the car. The new sills will be a perfect foundation to weld the new floor pans to. Check out the holes in the old frame rail at the bottom of the picture!

Where there is a 90 degree bend/join anywhere in the new chassis, I was originally intending to include extra metal to support the join. But there is no need to add the extra metal - it would just be adding redundant weight. With the front of the rear-suspension mounting points welded directly to my new chassis rails, I will nicely distribute the forces being pushed thru the rear axle as evenly as possible throughout the entire car.

This is especially important considering that the big-block up front is heavy, despite being on a diet of various aluminium goodies. Its weight will resist movement when the car accelerates - simply because of its momentum. I have therefore paid special attention to how the new chassis elements mount to the front frame-rails. Any connections pass thru both walls of the existing Mustang front-rails. Welding the new chassis onto just one face of the rail will not distribute the loads evenly and fatigue cracks would eventually occur.

The next few shots shows how I connected the 2" X 4" "sill chassis" to the front frame-rails. The connecting piece runs at an angle to the frame rails to promote strength but still allows plenty of room for larger tyres to fit. This angled connection should not only transmit acceleration forces cleanly to the front of the car but help control twist in the body shell too.

Firstly - measuring about a hundres times before cutting the holes in the frame-rail. The holes in the inner & outer walls of the frame-rail need to be offset from each other as the connecting piece comes in at a slanted angle (not a right-angle) as mentioned. This was tricky to get right!

Trial-fitting the connecting piece.....

Welded in place.... and a perfect fit.

Other side of the car now done too.

Photo from inside the engine bay showing the welding done to complete join.

This shot gives an overall view of the new chassis in place while I "trial fit" it with the outer sills removed. I'll soon be able to remove some of my "space frame" (to install the new floors, etc) as the new chassis is tieing everthing together again.

Below you can see the chassis finally welded in place with sills included.

And below is a shot showing what actually resulted - based on the original drawing I made (at the top of this post). It hasn't varied too far from the drawing. You can clearly see the zinc-coated box tube as it protudes from the front of the sills and connects to the front frame-rail, as well as the rear "stub" that connects to the rear spring-mount.

Not much chassis flex now!

Over and above installation of the "sill chassis", I am also installing the more conventional "sub-frame connectors". As I am replacing the floors and the front frame extensions, it is relatively easy for me (by way of the rotisserie) to install fully welded connectors. These will really tie things together and give me two protected channels within which I can run fuel lines and battery leads from the trunk area up to the engine bay of the car. But rather than weld the connectors to the front frame extentions via pieces of 3mm plate, I am inserting the connectors inside the rail extentions and then welding them in place. Fabricating things this way gets me two nicely protected tubes running from the rear of the car all the way to the engine bay.

Once the chassis is complete i'll be able to install the new wheel-wells (you can see in the photo's that i've alreay started them). The rear panels & wheel wells will probably be the next chapter.

Body Repairs - Rear Frame.

Every person that restores an old car gets some sort of surprise at how much more work there is in a project than they initially think. Very occasionally this is a pleasant surprise (less work) - but mostly not. Once I spun the car over I could fully see the extent of rust damage to the frame - the frame I was hoping to use to connect my new chassis elements to. Checkout the old welding repairs on the rear frames in these shots........


And yes... I had to angle-grind through the old sagging leaf-springs to get them (with the diff) out. Apart from severely rusted threads, the front leaf-spring bolts could not be undone as the bolt/nut heads were rounded off.

You can see the nice big rust hole in the frame rail right where the leaf-spring bolts up.

It was soon apparent that i'd either need to graft in full-length reproduction rear frame-rails or make up new frame rails from sheet steel. The cost of each repro' frame-rail is about $300AUD - so $600 bucks in parts (before any labour) would be needed if taking this option.

This seemed expensive so I did a quick internet search of specifications for "automotive" structural steel sheet and found that CA260S-G or CM350-G specification sheet were the likely candidates for me to build the rails from. These steels have the tensile & yield strength I am after, are great to weld and Bluescope Steel make the CM350 in the 2mm (80thou") thickness that I needed. But finding a supplier that could get me just one sheet is almost impossible! I could easily order it in 1000Kg lots, but just a few pieces is a big problem.

Something else that needs to be considered is the safety requirement to have frame-rail "crush zones" so the Fastback will actually deform in case of a serious collision. Weighing all this up with the added (many) hours needed to fabricate rails from steel sheet - I have elected to go for the reproduction frame rails. Now I "only" have to remove the old rails and graft in the new ones - still a lot of work!

The rear quarters, sills and tail panel were the next items to look at. I've described in a previous post how I found that both rear quarters had been replaced and pop-riveted in place.... well here are some shots of uncovering the joins and removing both old quarters.....


Check out the pop-rivet holes (below) where the quarter meets the sill! I had to drill out about 50 rivets all up on each quarter. I simply used an industrial wire-brush in the 9" angle grinder to remove the body-filler covering the rivets...

I used the new (2 piece) rear quarters as a template to mark and then cut away the old quarter panels (see photo below). I'm hoping to only use the main piece of the replacement panel -thus not use the second piece that incorporates the rear vent and outer rim of the rear window frame. I marked and then cut in a way that matches the new replacement panel but initially gives me about an inch of extra panel on the car so I can trim things back later if needed.
In the shot below (with some of the outer sill cut away) you can see patches on the lower-forward part of the inner sill. Thankfully, new box-tube welded along the inner sill (to create a hidden "full chassis" once the outer sill is put back) will strengthen this whole area up considerably. But the new chassis work will be in another post...


With the outer sills and rear quarter skins removed I can start to see what it will take to fabricate and add the new outer chassis rails. But I first need to install the rear full frame rails so I have a good foundation for the new chassis rails to connect to. My box-tube "space-frame" that is supporting the bare body needs to be suplimented at the rear to ensure there is no sag when the rusted rear-frame rails come out. So I added some support brackets and welded them from the space-frame to the body at various points (up under the back of the rear window, to the rear tail panel support, wheel-arch supports, etc). You can see where i've removed the old tail panel below. It give you great access to work on the rear-frames and wheel arches. But you need to be careful not to cut away the alignment holes in the tail panel support. These will be used to correctly centre & re-attach the tail panel.

I then drilled out the spot-welds in the floor & boot panels where they attach to the rear frame-rails, or, I simply cut out floor & boot panel with the frame-rail still attached - if it was rusted thru and needs replacing anyway. Keeping the old rear quarter panels, tail panel, front-seat platforms, etc gives me some original metal to use when putting in any required patches. The previous owner had at some stage replaced the inner rear guard panels - the ones that wrap up and over the rear frame-rails and form the outer floor of each side of the boot. So while these are salvagable, just about everything else that attaches directly to the rear-frames has to go. The rear-frames I purchased are from Dynacorn and each one includes the frame-rail itself, front & rear leaf-spring mounts, rear exhaust mounting nuts, rubber stop for the diff and even the outer seat-belt threaded mounts. While they are quality units and will provide a great foundation for the new chassis to weld to, I found one of them was mis-aligned when it was welded on their jig. I had to cut thru a few spot-welds, square the front spring mount up and re-weld it in place.

The rusted wheel tubs are being replaced by cutting out what's left of the inner & outer wheel arches but leaving the central "spine" of the original wheel arch in place. The "spine" (just my word for it) is simply where the inner & outer wheel arches are welder together to form a spine - which is then welded to the body shell up under the Fastback rear vents. You can see one new frame-rail in place below. Note the gap between the new rail and the inner wheel arch - this is where new sheetmetal will be grafted in.

Leaving the spine in place gives me a good template to follow with the new sheetmetal. The inner profile of the finished wheel arches I am making will be much more square in cross section when compared to the original wheel-well. The original wheel-well is formed by using pressed wheel arch halves - great for skinny tyres shaped like doughnuts but no good for whide rims with low profile tyres! The new wheel tubs will give much more room for the modern (square profile) wheel/tyre combo I intend to use.

Here is a shot of how bare the shell looked as I got close the end of the removal of all the "rusty bits". I am thankfull I built such a robust space-frame, otherwise the shell would have collapsed on the floor!

And finally, here are some shots of the new rear rails tack-welded or sitting in place. You may notice the following in these shots........

• Modified frame rail (on the right of picture) to fix dodgy welding & bent spring support.
• Use of 1/2 fibreglass rod to make sure both rear frames line up with the Mustang body.
• New sill chassis components sitting in place within the new outer sills (not welded yet).
• One outer wheel arch removed (just begining preparation for new wheel tubs).
• New rear quarters in place as an initial trial fit (they need to be lifted at the rear).

Just in case anyone is actually following this saga, I am well into the creation of the new chassis. But I need to actually finish it before I put up the next post. Hopefully in a week or two i'll be done as I have a long weekend coming up that should see me spend some time on the car. I would value any comments anyone would like to submit (they don't get displayed - unless you request it), I need all the encouragement I can get at this point!