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TD5 To Series III Bulkhead Conversion

TD5 To Series III Bulkhead Conversion

My bulkhead has reached the end of its life; in fact it should have been put down years ago! The top rail is totally shot, both foot wells are holed and rusted and at least one of the feet is seriously corroded. The answer is to either find a replacement – rare as hens teeth in good condition, purchase a converted one, very expensive with a long waiting list or make my own from a new bulkhead, the option I took.

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The old and very tired bulkhead

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Replacement TD5 bulkhead (Part No AHA710460, Panel Assembly Dash - £198.95 inc VAT as at 9th May 2008)

Amazingly, given the number of years between them, the changes between a Series III bulkhead and a TD5 are fairly minor and should be relatively easily overcome.

The basic plan is…
  • Remove the old transmission tunnel from the SIII bulkhead as it is required in the newly modded bulkhead.
  • Remove the hinges from the SIII bulkhead if as I do, you wish to retain a folding windscreen.
  • Remove excess brackets, lugs, captive bolts etc from the TD5 bulkhead.
  • Remove the transmission tunnel from the TD5 bulkhead as it is the wrong shape and size
  • Remove both foot wells from the TD5 bulkhead as again they are the wrong shape and size. (It may be possible to leave these if you are going to be fitting a modern heater and matrix and cable throttle – this is not covered in this article).
  • Weld in new Series 3 foot well repair panels
  • Weld in the old Series 3 transmission tunnel
  • Weld on the old Series 3 window hinges
  • Make any needed holes (including WaxOyl access points) and any other desired extra mods
  • Protect the bulkhead.
1. The old transmission tunnel is most easily removed by angle grinding it out leaving excess metal around it. This can then be removed and tidied up as required once you can start test fitting it in the new bulkhead. Make sure you don't cut away too much – study how it fits in the S3 bulkhead and how the TD5 one is put together before cutting – even as it is, having cut it out, I still have some nerves over if I cut out enough or not!!

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Series 3 bulkhead with the transmission tunnel removed

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Demo of how it will fit with the repair foot wells

2. Removing the window hinges is fairly straightforward. Just make sure you cut wide enough, they have an outward pointing lip on each side. You will find that they still won't come out after you have cut round – there is a strengthening bracket inside the bulkhead. However, it only uses a couple of spot welds and a cold chisel deals with them effectively.

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OS bracket showing lip

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NS bracket removed showing strengthening bracket

3. There are a fair number of excess bit to remove from the TD5 bulkhead. Each of them can be simply cut off and ground smooth.

This large bracket in front of the passenger can be simply removed, four welds.

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A captive bolt above the drivers footwell…

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This bracket above the drivers vent…

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On the engine side of the bulkhead, there are two pairs of spikes on the window rail – designed to fit in the bottom of a fixed window. Off they go…

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Lastly another captive bolt on the arch over the transmission tunnel…

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In addition, there are a pair of bolts (covered with plastic caps) a bracket and a captive nut on a bracket that I envisage *could* be useful in the future. For now I am going to leave them but they can easily be removed if required.

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4 and 5. It is easier and makes sense to remove both the foot wells and the transmission tunnel at the same time. For the main part it is a case of drilling out spot welds, lots of them (85 to be precise!). Spots should be removed from the side that you don't wish to retain – this means minimal damage to panelling that is to stay. In addition there are eleven welds that need dealing with as well.

Removing spot welds is a painstaking and slow process. You need to cut slowly to ensure the bit doesn't burn out, doesn't jump and that you cause no damage to other body parts. This strains drills which tend to heat quickly, so you have to break frequently to let them cool – this is just as well because it knackers your arms anyway! Basically allow plenty of time for this.

I started off across the transmission tunnel (two rows of spots inside the bulkhead) using a spot weld cutter. It's a clever tool that cuts around the weld and has a depth stop. It leaves circular nubbins on the underneath plate that need to be ground off. It did a good job as long as it lasted but soon started throwing teeth.

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The cuts

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Sheet folded back (note the scratches where the failing cutter started to jump around)

I then resorted to a solid spot weld drill. This is much more robust but it does rely on you manually checking that you don't go too deep. Continue across the foot well tops (inside) removing a double row of spots. Next continue down the side of the foot well. This line of spots is welded to a lip on the outside front of the bulkhead pillar.

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Across the foot well and down the wall

Next drill the spots down the door seal strip – from inboard, not outboard.

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At the top of each foot well/pillar there is a horizontal weld. You can't cut this without damaging the lip or internal structures (possibly with a Dremel). The alternative it to grind it as thin as possible – the leftover weld will still hold things and will be used a bit later….

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Remove the spots from across the other foot well (double row) and down the well wall and pillar door seal lip. There are also two horizontal welds at the top corners where the transmission tunnel meets the top of the wells. These can be cut… but with great care so you don't damage metal you want to keep.

The body side of the bulkhead is now prepared – turn to the engine bay side to deal with seven more welds.

The first is a single simple weld on a bracket on the drivers foot well, next to the transmission arch – just cut it, undercutting if necessary to free it.

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The last six are three on each foot well top support brackets – two outboard and one inboard outboard on each.

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The two outboard welds

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The single inboard welds

The outboard welds again can be simply cut, if necessary bevelling underneath a little to completely sever them.

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The double outboard welds cut

The inboard weld is another matter – it is pretty awkward. I found I could undercut one weld, but the other due to handedness was easier to cut vertically and then attack from inside the well once its position was established. Those who are contortionists may find it a bit easier than I did!

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Passenger side inboard weld, undercut

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Drivers side inboard weld vertically cut and ground from under.

That's it, ready for removal. Firstly work your way around all the spot welds with a cold chisel, levering and tapping to free off any spots that haven't 'let go' yet. Then enlist a helper or two and have them hold and steady the bulk head.

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All spots freed off

Remember the two ground but not cut welds at the pillar/well tops? They are still there and now they come into their own. From the engine bay side, carefully push the wells and tunnels at the bottom, swinging them away using the ground welds as hinges. It will be tough at first until the welds weaken, and in addition, some of the foot well sides/ spots etc may cause things to snag. On mine the driver's side moved very freely, but the passenger side needed a good club hammering on the foot well to free it past the bulkhead foot.

Then return to the body side of the bulkhead and keep folding the tunnel/foot wells combination back and forth, weakening the 'weld hinges'. In fact after a few wiggles, you probably have weakened them enough to tap through with a cold chisel. Once free, make sure your bulkhead is securely position – it is a delicate piece of body work when complete, in this state it is even more so.

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Working the tunnel and wells free

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Out and done!

6 and 7. Next job is to spend plenty of time grinding off any nubbins left from the spot welds and ensuring that all the to be welded joints are taken back to clean metal. I then used UPOL Weld#2 Weld Thru Zinc Rich Primer. This stuff is great. It means that the weld joints are protected, and yet the primer is stable so that the welding activity does not disturb it. The last thing you want is moisture getting into the joints and rusting them out!

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The transmission tunnel in UPOL #2

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One of the bulkhead legs protected

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Window brackets and internal support brackets in primer

I was very fortunate in being able to borrow an air powered punch. This enabled me in about 10 minutes to punch holes through the metal to enable plug welding (welding filling up the holes to attach pieces together and so mimicking spot welding). You can make them manually with a drill bit, but this will take quite some time.

After that, the wells and then the transmission tunnel were clamped in place ready to be welded. We started off with the bulkhead ON the chassis to ensure against warping or misalignment.

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Wells clamped in place

Both of the footwells and the transmission tunnel were tacked utilising a few of the newly punched holes. You will probably need numerous clamps to hold everything in the right positions as the parts are quite springy.

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Drivers well tacked to the transmission tunnel – note the row of holes ready for plug welding

A few tacks are added from the other side as well. I had the roof still on and so with the windscreen in place was able to position the window hinges and tack these on, more on them in a while.

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Everything tacked up

The bulkhead is removed from the chassis for easy access to all the welding. There are an awful lot to weld, and care must be taken to not forget the seam welds on the engine side and four on the internal side. In addition, the engine bay side arch over the transmission tunnel was slightly proud of the tunnel. A hammer soon knocked it back so it could be also welded.

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Arch over trans tunnel knocked back for welding

Going back to the window hinges, original Series uses rivnuts aka nutserts to mount the internal clamps. Instead, I decided to drill right through the bulkhead and eventually use nuts and long bolts. This will prevent any danger of the rivnuts working loose. The holes were marked and drilled carefully prior to tacking and then welding on the windscreen mounts.

The internal support brackets were also then welded in place.

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Passenger side internal support bracket

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Central support bracket

The last welding step was to eliminate the excess holes that have appeared over the years. This is done by simply cutting little squares from some off cuts (the TD 5 foot wells that have been removed are handy!) and plug welding them on through the holes.

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Welded on scrap

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The other side, before tidying.

The next step is to grind all of the welds smooth, and grind all of the hole filling scrap off. With some care and time, you can get great results…

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Tidied up welds

The bulkhead was refitted to the chassis so that various ancilliaries such as heater boxes pedals etc could be test fitted and any extra holes required could be drilled.

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Some test fitting

The last part of this stage was to refit the window and bonnet to ensure that the window folds correctly, (it does!) and that the bonnet fits. The rain gutter is a different shape with the TD5, and even though the bonnet does fit without interference, it is actually so close, I decided to shorten and narrow the ends of the rain gutter just to make sure.

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Window and bonnet on

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Window folded down.

I plan to make some large holes in the bulkhead for future WaxOyling but they have to wait until I have sorted out my dash for positioning.
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JayHoe
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