This blog is intended to document the build of my Gardner Douglas Mk4 Cobra; partly as IVA evidence, bit primarily to help others learn from my mistakes and/or successes.

I will endeavour to post as often as possible, with a view to entering a single post for a particular element of the build process, however inevitably some things may not be completed in one go. All posts will be tagged so it should be easy enough to find the information you seek.

Please subscribe to receive emailed updates and feel free to post any comments or questions which I will make my best efforts to respond to.

Tuesday, 20 September 2016

Engine Update

I was originally planning on using an LS3 with T56 Magnum 6 speed gearbox but as the cost of this combination is around £10K I started exploring other options.

Although there seem to be plenty of small block Chevy and Ford engines available I want a modern engine so started looking at Audi, BMW, Jaguar/Range Rover and Lexus.

The 4.2 Audi V8s are plentiful but trying to find a suitable RWD gearbox is near impossible, I did briefly consider building a Quattro Cobra but shelved the idea.

BMW M62 engines are also affordable but I have heard that wiring them is very difficult so decided against that.

Jaguar and Range Rover engines are also readily available but do get quite expensive if looking for power.

So that leaves Lexus. The 1UZ-FE engine is found in LS400 and SC400 UK registered cars from 1991 - around 2000 and whole cars can be picked up cheaply. The pre-95 cars had stronger conrodssoncan handle a lot of power without modification and the 98 on engines received VVTi which bumped the power up from 260bhp to 280bhp and increased fuel economy. 

I managed to buy a low mileage (127K) 1998 LS400 with current MOT for £550, so it comes with the VVTi engine and 5 speed auto.  Having an MOT meant I could give it a good shake down on the run home and it ran like a dream. 

Another bargain I found was a M112 suoercharger which I got for £300.  It came off a Jaguar X350 4.2 and they even threw in chargecoolers for free. I'll probably put it through the IVA in standard form then shoe horn the Supercharger on afterwards. 

These engines are known to be extremely strong and reliable but only ever came with auto boxes, however do get transplanted in to lots of drift cars so it is possible to convert them. I plan on either using a BMW 6 speed or a Supra Turbo 5 speed by means of an adapter plate and bespoke flywheel. 

                              1st   2nd   3rd   4th   5th   6th

BMW ZF-S6-37  4.35 2.45 1.68 1.23 1.00 0.85

Supra R154        3.25 1.96 1.31 1.00 0.75

The Supra gear ratios seem preferable with the GD Euro rear diff but the BMW gearbox is cheaper, more available and known to be very strong so the dury is still out on this one. There's also the issue of IVA/DVLA and the 'one major reconditioned part' statement which might force me to buy a brand new box. If that's the case, I might go for the T56 after all.

LS400 giving up its heart

Tuesday, 23 August 2016

No More Bling

I never really wanted a Cobra with loads of shiny Chrome as I'm trying to build a modern alternative, but didn't think there was any other option for certain things such as the windscreen so just settled for it.

After recent discussions with fellow builders, I have decided I am going to go 'bling free' after all. The chrome/shiny bits I already have are:
- Windscreen frame and stanchions
- Fuel filler cap
- Headlight surrounds
- Wiper spindle ferrules
- Wiper arms and blades

The wiper arms and blades haven't been fitted so I will see if I can return them to GD and I'll buy black ones, I think Classic Mini ones fit.

I have made enquiries with a few local powder coaters and the consensus it that Chrome can be coated after being shot blasted to ensure good adhesion, and cheaper than I was expecting too.

I now needed to remove bits from the car, the headlight surround and wiper spindle ferrules just unbolt and the Aston filler cap needs a couple of roll pins knocking out but the tricky bit was the windscreen.

The powder coating process involves oven baking which isn't good for the rubber seals which meant the glass had to be removed and after speaking with Brasscraft (they make all the UK Cobra screens) I was assured it was possible.

The frame is made of two sections, the lower bit that sits across the scuttle and the rest. These are held together by 2 flat head screws at the bottom of each side. A sharp flat object needs to be run around between the seals and the glass, I used a 6" steel ruler. I then used a flat head screwdriver to prise the lower corners apart, I could then gradually ease the two sections apart.

The top frame is more difficult as it wraps around 3 side so there is more friction in the seals, I had to resort to a nylon faced mallet here! Whilst holding the glass, I lightly tapped the corner of the frame outwards each side, then upwards from the bottom.

This process was repeated gradually each side until I could pull the frame off the glass, thankfully with everything still in one piece. Now the seals can be removed for reuse when it all goes back together.

Two roll pins for the hinge and catch removed with a hammer and punch

Glass removing tools! 

This shows the two screw holes at the lower edge on each side. I'd already removed the lower frame before I remembered to take pictures. 

Prising the seal off the glass, a Stanley blade would probably have been better in hindsight. 

Two parts of the frame ready for the powder coaters 

Saturday, 20 August 2016

Fuel Filler Cap

I actually fitted the fuel filler a while ago but never wrote it up.  GD offer 2 types of filler, Aston Style and flush fit, I went for the Aston style.  This is a decision that needs to be made at the body order stage as the relevant recess need to be bonded in place.

The first thing to do was rub down and polish the fuel filler recess, this was done by hand due to the confines of it.  The centre of the mounting surface was found and an 76mm hole was cut with a holesaw.  

The Aston filler cap comes in two parts, the threaded flange and the cap itself.  The two parts were separated and the flange bolt holes drilled to 5mm (these were already pre-marked on the underside) and countersunk.  With the flange held in position on the car I then drilled through for one of the mounting holes, then bolted it in place to drill the rest.  The flange was then removed again to make the gasket.

I used countersunk Allen head bolts, but you could use button heads.

I bought a large roll of 1mm thick rubber gasket material off ebay along with a tool to cut circles (basically a compass with a blade attached) and some punches for the bolt holes.  I then made my gasket at 135mm diameter with a 76mm diameter hole in the middle, remember to cut the outer dimension first otherwise you'll have no centre left for your compass point!  With the ring made I placed it on the car under the flange and marked bolt holes which were then punched out.  I used an M6 punch just to give a bit of wiggle room for the bolts.

Gasket cutting made easy with cheap tool (left)
Bolt holes punched and gasket offered up (right)

The flange and gasket were then bolted to the car and the cap screwed on.  Initially it didn't tighten up in the right place.  The cap comes with several shims, the thicker red ones are 1mm think and the thinner blue ones 0.4mm thick.  After some experimentation I needed the 3 thick ones to get the cap to sit in the desired position.

Bolted on to car, looking lovely (although I may still get it powder coated black yet....)

Rear wiring loom

There are four main looms for the car:
1. Front
2. Rear
3. Dash
4. Engine

The Font loom has already been installed, although not exactly as per the GD manual, see this link for the blog post.  The dash loom can be purchased from GD (which is probably preferable if using the standard layout) however I will likely create my own as my layout will be different.  I already have an LS3 engine loom, that will stay in the cupboard until I get the engine.

To start with a pilot hole was drilled from the boot in the bottom left hand corner above the rear axle tunnel, this appeared behind where the passenger seat will be. I then opened this out to around 15mm and cut a strip out below this to allow the loom to fold downwards.

The loom is then fed through bit by bit from the cockpit, around the near side and behind the boot latch striker plate. The front part goes down the rear bulkhead, along the transmission tunnel then half way up the front bulkhead where it will meet the front loom behind the dash.

Within the boot, the loom follows the corner down the axle tunnel, across the floor and along the rear edge finishing at the offside rear lights. There are 3 main bunches of wires:
  1. Fuel system (fuel pump, level sender)
  2. Nearside rear lights
  3. Offside rear lights
There is also a lead just as it enters the boot for the number plate light and provision for reverse and fog are available at either side rear lights.  The loom comes with crimped bullet connections but I've changed these for Superseal connectors (for the lights at least) as they lend themselves better to being disconnected/reconnected repeatedly and offer a more OEM look.

Drilling hole in to cockpit area

Loom behind passenger seat position (looking rearward)

Number plate light lead just inside boot

Fuel system bundle

Nearside lights

Loom goes behind boot latch plate to offside lights

Superseal plugs

Rear loom connects to front loom behind dash (black & white plugs)

Windscreen Washer

Now that the daunting bit of fitting the wiper spindles is done, I turned my attention to the washer system.

In an effort to keep the engine bay as clutter free as possible I have decided to install the washer bottle in the offside wheel arch compartment (idea shamelessly stolen from Rob's blog), I may also install a float switch to tell me when it's low.  The bracket for the bottle is fitted to the inner wing and the bottle just clips in.

Like many others I've opted for a single washer jet in the centre and this was install 40mm back from the rubber seal of the windscreen. A simple 8mm hole and nut on the back, the hose then follows the wiper bundy tube and enters the wheel arch compartment above above the pedal box. The wiring will also follow the same route for the pump.

Tube will be cable tied to Bundy tube

Tube enters wheel arch compartment above pedal box

Bottle fits snuggle in wheel arch compartment
Washer nozzle looking neat and tidy

Tuesday, 16 August 2016

Windscreen Fitting

I like a good 'shape change' to show progress so it was time to fit the windscreen. I removed the support legs from the windscreen by undoing the 4 screws each side then put the screen back in a safe place. I've read a few blogs where jigs had to be made and bonded to the body to transfer the mounting holes to the legs but my legs were already pilot drilled.

There is also a drawing within the build DVD files so I transferred these measurements on to the legs to check the pilot drill holes. This showed that they were the right distance apart but slightly off the centre line. I figured that I could elongate holes if need be so opened up the holes to 8.5mm, slowly and with light pressure to avoid the drill grabbing the brass.

Next I cleaned and polished the scuttle area before drilling a line of holes where GD had already marked the scuttle each side. These were then filed to a rectangle and gradually opened out until the support legs slid through easily and the mounting holes lined up. I then removed them and refitted to the windscreen before sliding the whole thing back in, this can be done on your own by standing in astride the transmission tunnel but it is much easier with a helping hand.

I had to shim the legs out a bit with penny washers between the legs and mounting points each side. There needs to be about a 6mm gap between the outermost points of the lower frame and the scuttle and 930mm from the top of the windscreen and the rear bulkhead return, the rake angle can be adjusted slightly by elongating the mounting bolts slightly if needed but mine was spot on. I also measured the distance between the edge of the frame and the top rear edge of the door opening, both sides should be similar and again mine were pretty much spot on.

The centre stay bracket is awkward. I first placed the lower piece on the scuttle lining up the screw holes in the frame and marked where it will sit. Next the screen was removed and bracket laid in place so I could mark and drill the holes. The two brackets and centre stay was then installed on the screen before putting it back on the car, the tricky bit was getting the button head bolts through the scuttle, but needle nosed pliers helped here. These will require a cut down allen key when I finally tighten them up, but for now they are left loose as the screen will come off for safe storage.

The screen will stay fitted for now while I mark up for the windscreen wipers and washer jet, then  it will be removed and the gaps around the stanchions filled with silicone. 


Stanchions were already pilot drilled, markings are as per the build manual

Stanchion slots were pre-marked by GD, these were chain drilled then opened out with a file

Nearside stanchion installed
Looking more car like now

Centre stay fitted

Windscreen Wipers

I have been putting off fitting the wipers but it was time to bite the bullet and get on with it so the screen could be removed and stored safely again.   

The build manual states that the spindles should be 415mm in from the outside edge of the screen stantions and 5mm forward of the screen rubber seal so these measurements were marked on the scuttle. I then used one of the rubber gaskets to mark the elliptical hole. This left a measurement of 512mm between spindle centres.

I then assembled the wiper motor, bundy tube and gearboxes on the bench after bending the bundy tube to the curve of the scuttle.  The measurements between the spindles on the bench proved to be within a couple of millimetres so I was happy to proceed.

Using one of the outer ferrules as a guide I pilot drilled the holes in the scuttle, gradually opening out up to 12mm.  The holes were finished with a round file until the spindles fit through. The inner ferrules weren't the right angle so needed filing down to match the outer one, which also allowed for enough thread to protrude. 

With everything reassembled it was installed on the car, initially with the spindle gearboxes facing forward but the motor didn't seem to want to line up very well so I turned them around and moved the motor further forward on the mount. I'm still undecided on which way is best so may come back to this again later.... 

The motor is installed on the lateral under dash bar with a strap and rubber pad using M8 bolts. It may need to come ofc again yet as can't judge where the park position is until power is applied. 

Measurements transferred to scuttle 

Bench assembly

Near side spindle fitted 

Gearboxes facing forward.. 

.. and rearward. The jury is still out on which way is better. 

Saturday, 9 April 2016

Front wiring loom

The front loom has been a bit of a puzzle, especially within the cockpit area. I started by identifying and labelling the various parts of the loom using a combination of GDs wiring diagrams and the written instructions. Although this isn't difficult, it is time consuming but definitely time well spent and it certainly helped make sense of how it would be routed.

The standard GD method routes the front part of the loom out in to the engine bay through a 44mm grommet with the engine loom connectors, it then goes under the lip of the bonnet opening. I want to keep the engine bay as tidy as possible so I altered this slightly.

I pulled the front part of the loom (lights, radiator fan and horn) back through the big grommet leaving just the two engine loom plugs and the earth leads to go through the grommet. I then drilled a 20mm hole above and right of the heater ducts (looking forward) and routed the front part of the loom through the wheel arch compartment before going through the inner wing and appearing under the lip in the engine bay.

The loom then splits adjacent to the bonnet hinge; headlights/indicator/side repeater back through the nearside inner wing to the left and the rest to right under the nose cone and through the offside inner wing. The horn lead sits on the engine bay side of the nearside inner wing and the radiator fan cable hangs down in the middle under the nose cone.

Within the cockpit the relays have been mounted upside down in the nearside footwell and the heater fan & battery cable fed through the same hole as the front part of the loom in to the nearside wheel arch compartment.

Grommets have been used where the loom passes through bulkheads and it's all held in place with P-clips.

Relay block fitted with self tappers, just spotted that it's not level so adjustments necessary 

Nearside wheel arch. Head and side light cables to the left, side repeater cable going from left to right

Loom along inner nearside wing

Loom across nose cone, the cable dangling down is for the radiator fan

Friday, 8 April 2016


Before I could install the front wiring loom I needed to underseal the front wheel arches and nose cone. I bought Hammerite Underbody Seal from Halfords (I have a trade card :-D) and dug out an old paint brush.

Every edge was masked off to avoid having to clean it off afterwards, this took ages but preperation time is seldom wasted. When I opened the tin I thought I must have a duff batch as it was stiff, I expected it to be like a thick paint that would set hard. It turns out, it's supposed to be the consistency of a paste.

The instructions say to apply with a brush up to 2mm thick however I applied it thinner and will go back for a second coat, hopefully this will give me a better finish. It's quite hard work due to the thickness and working mostly upside down but the front wheel arches and nose cone have been done and the rear arches have been masked off ready. If I have enough left after that I may do the rear axle tunnel too.

I also bought a spray can of Hammerite Stone Chip Shield which I used for the lower sills.

Pretty thick stuff

I went through quite a bit of masking tape

Offside wheel arch after first coat

Nose cone after first coat

Sills sprayed with two coats 

Thursday, 7 April 2016

Accelerator pedal

The GM LS wiring loom I have comes with an electronic accelerator pedal but there isn't enough room to install it next to the pedal box so some creativity had to happen.

Andy from GD had mentioned something about mounting it on the other side and connecting it to the accelerator. I first cut the pedal off ensuring I left as much of the lever arm on as would fit within the wheel arch compartment to give the most amount of travel. I also had to modify the shape of it to allow the clevis to fit. It was then offered up, the holes marked and drilled in the bulkhead.

To remove the accelerator pedal I had to loosen all the pedal box mounting bolts which is easier said than done, but I manged it but putting one are through the footwell extension hole. Once removed a filed a couple of flats on the end pedal arm and drilled a 6.5mm hole for the clevis pin. The pedal was bolted back on but the 20mm hole I had drilled in the bulkhead for the turnbuckle wasn't quite right so this was extended down.

The turnbuckle I had was a little short so it was extended with some M6 threaded stainless rod an extension nut. It was then connected and adjusted so the accelerator pedal is the same height as the others.

I haven't ended up with quite as much travel as I'd hoped so I may have to move the turnbuckle fixing down the pedal arm later.

Modified GM accelerator pedal 

Modified GD accelerator pedal 

Turnbuckle connected in footwell 

Modified GM pedal in wheel arch compartment, thete is still plenty of room to get the plug in

Heater box take 2

If you've read my previous post you'll now know how not to fit the heater box! To repair this first effort I sellotaped over a small piece of plywood and taped that over the holes in the passenger footwell, then filled from other side with P40.

This time, I marked the centre of the heater on the lower rear edge the offered it into position before dismantling it, I then marked across the bottom edge and transferred the centre line on to the body.

The heater was again taken apart and the empty box held in position using the marks made in the previous step, I then sprayed through fan mounting hole with some primer I had lying around. This outlined a rectangle and screw holes where the outlets fit.

Two of the holes were pilot drilled which allowed me to fix the outlet ports to the footwell bulkhead with self tappers and mark the holes. These were then drilled out from the footwell side.

To mark the mounting bolt holes I placed a few layers of masking tape on the front of the bulkhead and; with the outlets installed and mounting bolts screwed in from the inside, pressed the box in to position. This was enough to mark the tape so these were drilled out to 10mm to give me a bit of wiggle room.

Now the heater can be reassembled and bolted in position to mark the heater hose outlets. I had already pilot drilled the holes for the battery cables so used the top one of these as a reference to measure from to the straight outlet. These measurements were transferred to the engine bay side and the first hole pilot drilled. I then measured 65mm rearwards from the other outlet and pilot drilled again, the holes will be opened out fully when the engine bay bulkhead has been gelled.

The heater has been removed again for now while install the wiring loom.

Mounting bolts inserted wrong way around to mark bulkhead

Installed as seen from footwell, you can see how far out I was the first time! 

Installed from wheel arch compartment, I used the upper of the two battery cable holes on the left to measure from for the outlets

Tuesday, 5 April 2016

Heater box take 1...

So this was my first major cock up on the build, thankfully it's only inside the battery/heater compartment and not on the outside!

The manual states that the heater needs to be mounted as high up and as far outboard as possible which makes perfect sense. I started by dismantling the heater so I was left with an empty box with no ends on, four M8 rivnuts (I would have used M6 but the nozzle for my tool is broken) were installed ensuring the bottom two wouldn't fould the heater matrix.

I then made a cardboard template which was offered up as high and outboard as possible, holes marked on the bulkhead which were then drilled out. I then put the two outlets back on the box and made sure they fit which they did, great I thought.

What I didn't consider was the fact that when the matrix is back in the outlet pipes protrude inboard and prevent the whole assembly going high enough, so my holes are too high.....doh!

These will need filling and I'll start again....

Heater box fully assembled 

Heater box fully disassembled 

Cardboard template put in wrong position, do copy this! 

Even worse, loads of holes in the wrong place, out with the P40