Marks Cobra Build

Body and wheels

Body On working height frame

wheels and tyres fitted

The body is back home now fitted to a trestle for good working height. Ill start collecting the materials and equipment together to tackle the molding edges and flashlines etc.

The wheels have also been delivered, I went with the 18″ CHB wheels from Image ordered through GD. I’m very pleased with the rear wheel offset finding those E type rear axles has definitely been worth the effort. the dished look is just very right.

Image Wheels CHB

http://www.imagewheels.co.uk/chb-alloy-wheel/

Tyres : Michelin Super Sport:-

275/40/18 rear
245/40/18 front

Just trying the boot lid against the rear wheels to get a feel for the colour scheme. The plan is red wheel bands on the rims and some red accents on the car but all the metalwork including windscreen and roll bars in satin black – like the wheel finish.

So Thats Black Stripes on main background colour Ral715 with red accents

Original Plan was to have sidepipes but as time goes on I’m swaying towards no sidepipes Photoshopped out the side pipes and added some graphic. Ok this graphic looks OTT but may do something more subtle in place of the pipes?

Body Arrives

Body, Uncategorized

Just a little later than planned I’m now the proud owner of the MK4 body. I collected it together with a host of other stuff at the end of May. I’m very happy with the color choice its Ral715 slate gray.

My Mk4 on the left

The car with the stripes is another of Andy’s customers its a MK3 in a much darker painted grey with very subtle stripes very nice indeed!

The gelcoat finish looks very good. At one point I was going to Ask GD to do the flashline removal and panel fitting etc. but after further consideration I thought it was something I would rather attempt myself…. so on the road and back North she goes to receive some tlc….

20160527_102121 — Collected on beaver tail trailer, journey went without a problem.

Engine Gearbox and Clutch

Clutch, Engine, Gearbox

The LS3 crate engine and Tremec Magnum gearbox has arrived.
Slight problems to resolve.
The yoke I had acquired was a 27 spline yoke from the tremec t56 unfortunately it does not fit the magnum gearbox.
The Yoke needed for a magnum transmission is 31 spline as detailed.

Dana Spicer 3-3-5961X
1350 Series Slip Yoke 31 Spline fits Tremec T56 MAGNUM and TKO 600 Transmission
Length to center of u-joint… Dimension #1 = 6 1/2 inches
Barrel Diameter… Dimension #2 = 1 11/16 inches
Barrel Length… Dimension #3 = 4 1/2 inches
U-joint cap diameter… Dimension #4 = 1 3/16 inches
U-joint width… Dimension #5 = 3 5/8 inches
Series… 1350
Spline count… 31

magnum yoke

Good news – called GD and sounds like they have one in stock. Ill order up a full propshaft from GD as soon as I do a trial fit of the engine.

Tried the engine and transmission in for size and works out the prop gap is about 366mm I guess the actual prop length will be something a little shorter than this with an allowance for a bit of clearance on the sliding spline.

Clutch Trial Fit

What on earth was I doing a clutch trial fit for you may well ask, well the truth is I wasn’t meant to but after fitting the clutch and pressure plate housing I started to do a bit of reading up to find out what the odd looking connection was on the slave cylinder. Whilst searching for information on the slave cylinder fluid input fitting which turns out to be “Quick Disconnect Fitting” I also discovered that I had inserted the pilot bearing the wrong way around. It said nothing on the instructions I received with the installation kit about direction for the pilot bearing and although I did notice it had a slight difference I chose to put it in with the needle bearings visible and closest to the transmission. My logic was simply to get the needle bearings further along the shaft end.

Turns out my logic was wrong and the bearing goes in with the closed end towards the tranny, obvious when you realise that this is the grease seal end. OK so the clutch has to come back off – no big deal but how the heck will I get the pilot bearing out that i just drifted in with a 3lb hammer? My first thought was, OK its just going to get butchered out and buy a new pilot bearing but a quick google check and low and behold some genius on youtube had figured out a 3 minute solution. All I had to do was pack the centre of the bearing with grease and insert a close fit (15mm) drift through the centre of the bearing, strike it with a hammer a few times and low and behold the bearing jumps out. Extreme Hydraulic pressure pushes it out from behind – what a good trick – and it works – youtube to my rescue!

Now on to the problem of that Quick Disconnect which got me searching in the first place. Apparently these fittings are used quite extensively in the USA and the idea is to enable disconnection of the slave cylinder for removal of transmission during clutch service etc. without introducing air into the system so alleviating the need to bleed.

The Quick Disconnect is the big orange part in the picture. The other opening is for the bleed nipple which is lengthy so it can just be bled from the bellhousing opening. I’m going to fit external bleed flexi pipes so I plan to modify both of these fittings. Pretty easy on the bleed side since its just an m10 fitting, so a standard male end of a flexi would work here but the quick disconnect is not so simple since its fitted into the slave cylinder aluminium casing with a flat o ring and groove, held in place with a roll pin. I think the simplest method here may be to cut this orange bit off and have the blank pipe end threaded to m10 with a taper. That way I could fit an m10 female/female extension fitting, effectively replacing the orange part with this.

m10 female

I’ll figure this out over the next couple of days and report my solution here.

Trial fit to get prop length

Things are starting to get heavy LS3 and Tremec Magnum in place.

Engine back out to sort the clutch slave issue here’s a pic of the new fittings. The banjo fitting on top is for the remote bleed flexi this replaces the long brass bleed screw (above). The setup on the lower input shows the new fitting that replaces the ‘quick disconnect’ (orange plug above). It was easier to turn this fitting with a standard male metric brake end as shown, but since I already had my flexi pipe with a male end just adding a standard female/female coupling in between joins it all together.

clutch slave fitting

With this complete I can re-install the engine and gearbox in the chassis.

Brakes

Seem to have all the brake lines connected now… I had a moment of doubt, the brake line fitting kit I obtained (which includes the majority of the brake lines and T junctions), had the same flared ends at each end of the lines ( ie. a double flare).

This is a picture of the double flare (concave) on pipe end and in this circumstance I have no doubt it is correct since it is mating to a male (convex) fitting. However, at its other end you can see it is going inside a T junction and the T junction is concave internally, therefore I might have expected this length of pipe to have a bubble flare (convex) on opposite end… hmmm curiously all the ends are double flares.

I wasn’t expecting that and pondered whether to follow this logic for the other connections I had to make myself ie. the ones going into the callipers. I did do a bit of google research on the subject and found some suggestion that double flares can be used in all circumstances (male and female counter ends) and may have better reliability when used in circumstances when the fitting is connected/disconnected repeatedly. (maybe a brake expert can chip in on this one because I’m still unsure).

In the end I decided to follow the same logic as the professionally supplied lines and double flare each end.

The Jag calliper support brackets I acquired are a little shabby, so my son made me some new ones in stainless steel. Good Job Josh ( I knew he’d come in useful one day….:)).

Handbrake Calipers

Well as much as I was pleased I didn’t have to strip the jag parts myself ( I acquired these from someone’s aborted build ) it does have the odd drawback, here’s one.
I sent the handbrake callipers off to Wards to be refurbished not really knowing some parts are missing.

Once I offered the handbrake cable up I realised the parts where missing some critical bits (the swivel block ends). I then tried to order the ends from Wards only to be told those parts are not available separately, and the ends should never be taken out…
Oh well not to worry – who needs a handbrake.

Body update

Body

Not had much to do lately, simply because I have no other parts… things should start getting real busy soon. Just had confirmation my engine gearbox clutch etc. are all arriving next week. then I can start with engine installation wiring etc. plus Just had confirmation from Andy that body is still on schedule for early May. Sounds like I’m first in the mould after Stoneleigh so lots of action coming shortly. I have to confirm the colour to Andy next week… out with the RAL charts ral-k5-faecher

Bumpsteer

Front Suspension

Setting the bumpsteer was interesting I firstly tried clamping straight edges and using line of sight to keep them parallel. This did identify how far out it was to begin with (quite a bit) but I didn’t feel confident about achieving the best position this way since it was difficult to perceive very small changes.

Out with the trusty Hilti Laser (this is a self-levelling type of laser so I clamped that on the wheel disk fired straight ahead, in the direction of travel onto the garage door a few feet away. After some plotting of curves it quickly becomes obvious that you can’t really do it this way since the observed travel is a combination of bumpsteer together with scrub (the in/out movement of the wheels caused by the wishbone radiuses) and camber change effect (caused by the unequal wishbone lengths). Geometry-Model wishbones

You could use the above method by calculating the amount of scrub then plotting the curve that is created by the radius arm travel Then whilst measuring bumpsteer the best line that could be achieved is the compound curve shown above right. But even then you would also need to account for the camber change that is happening throughout this movement.

The method of shooting the laser perpendicular to the wheel disc is better because this eliminates the scrub effect since the laser will not move “off line” due to scrub, it moves off line only due to bumpsteer. ( plus a bit of vertical change due to camber change).

You could use a mirror clamped flat to the disk and fire the laser at the mirror as has been suggested before but I’m not convinced what the mirror brings to the party, I feel it just complicates the setup.

With a couple of simple clamps fixing the laser approximately perpendicular to the disc at any point will allow exceptionally accurate readings to be made very swiftly – horizontal movement of the laser line only represents the element being induced by the steering arm…. Job done.

The further away you can put the target the better since any slight movement is exaggerated, in my case I was able to get an almost vertical line at 4m distance that’s definitely zero bumpsteer (well near enough). Again well done GD for excellent geometry around the steering rack chassis elements. This would not be possible unless everything was in excellent geometric harmony.

Ok that’s the end of this boring bit (Civil Engineers white helmet off – petrol head back in place…..)

Did I mention I was impressed with GD’s chassis geometry J?

As you can see I have been rather milking this part of the build simply because I have no other parts… However things should start getting real busy soon. Just had confirmation my engine gearbox clutch atc are all arriving next week then i can start with engine installation wiring etc. plus body is still on schedule for early May so lots of action coming shortly..

Alignment and geometry

Rear Toe

And now the Civil Engineer in me comes out… Prepare to be bored by this bit.

Setting up the caster and cambers on the front and camber on rear is relatively straight forward and well covered elsewhere, however I seemed to find a lot of ambiguity regarding the rear toe set up. Consensus suggests there should be a slight toe setting but how much?

GD suggest “10 minutes (with 10 minute tolerance)” so that suggests 0 to 20 minutes is acceptable?

Haynes manual states rear “wheel alignment Parallel +/- 1/32” or (0.08mm)” they must have a decimal place typo since that’s 0.8mm. so that suggests acceptable range of -0.8mm to +0.8mm

Jaguar Wheel Alignment Data (from Jaguar dealership see below)

This is helpful, it gives the data 3 ways and clears up a bit of mystery/ambiguity I think.

Toe in mm 0.8 (+/-0.8)

Toe in deg 0.10 +/- 0.10

Toe in deg 0°6’ +/- 6’

I’m going to assume all of these measurements are a combined measurement (ie the total toe between the wheels), so a toe of 10 mins would mean 5 mins at each wheel. Therefore, I’ll aim at 5 minutes/side. Jag data specifies anything between zero and 12mins combined (zero and 6 mins per side).GDs figure of 10 minutes refers to combined toe so that’s 5 minutes per side… Voila everything’s on the same page more or less, I’m happy and your bored!

Geometry-Model

Rather than try to measure 0.8mm over 15” it is much easier to set up a string line system (fine thread or braid is great for this) to measure 3mm over 2.4m (which is a nice distance to gauge an accurate setting), and conveniently is the approx. distance between centreline of rear axle and steering rack so easy to set up a nice square. I have to comment at this stage on the accuracy of the Chassis – so far I have been extremely impressed at the accuracy obtained in manufacturing the chassis, which translates into very little and even shimming of running gear components. I know how difficult this kind of accuracy is to achieve – so “hats off” to GD for their Jig work!

ISL_7954

Couple or recommendations here.

1 – make absolutely sure that the straight edge you use to clamp to the disc, which acts as the alignment throw for the toe measurement, is absoluteley straight and perfectly clamped to the disc. Any tiny amount ‘out of true’ for your staraight edge will make this measurement useless.

2 To adjust the toe use shims between the wishbone carrier bracket and the diff to achieve the desired toe of -3mm at 2.4m away – but I would suggest removing the GD back carrier bracket before making these adjustments. It was my experience that the holes in this bracket are very “tied up” to the shaft diameter therefore it was impossible to correctly adjust the toe with this bracket in place. All you would be doing is inducing stress into the shaft and needle bearings in the wishbone bush. Once the correct toe is achieved offer the bracket back in place and make any adjustments to the holes filing as necessary. On my set up slight slotting of the holes was necessary to enable perfect fit and inducing no sideway out of alignment stresses onto the shaft ends. Only then torque this back bracket back into position.

Suspension Front and Rear

Front Suspension, rear suspension

Found the short Drive Shafts and Wishbones, these aren’t essential as I already have the standard ones but I really prefer the deep dish on the rear Wheels – Keith A has used these same shafts on his build and has recently acquired his wheels – they look just right.

On Cue received the Diff and hubs back just before the Easter break so that gives me plenty to go at Easter Weekend.

I have identified a small problem with the front wishbone bushes. I used Superflex bushes after and could not get them to close up properly. In the end I had to dismantle them and take a closer look. Turns out the internal crush bushes as supplied by superflex measured 37mm. This just wasn’t allowing the bushes to compress and i worked out 2mm needed to be turned off the internal bush length. Just to be certain Keith A sent me some close up pics and measurements of his set up and these confirmed the bushes need to be 35mm. I called Superflex and they were helpful but too slow. By the time they sent me revised bushes I have already turned the originals down to size and everything fits fine now…

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-45209203189216__1080x608-ARGB_8888-1964174781

Rear Axle put together on the Saturday and chose to lift it in since I already had the front end built up so it was getting a bit heavy to lift the chassis – seemed easier to lift the axle with the help of the engine lift and a jack to control the angle it went together superbly. Compliments to GD jig work as these bolts around the diff are pretty tied up little room for error when the weld the frame up.

On with Alignment rear toe front caster and camber etc. 4 degrees old skool or 3.9 degrees new skool…

Almost A rolling Chassis – just as well since I have the engine scheduled for delivery in a weeks time so now I have somewhere to put it. ISL_7943

Mark T – GD Cobra Build 2016

Introduction

Well the truth is I’ve never been that much of a fan of originality. I appreciate that its exactly what some people want but each to their own. My ideal is a car that looks superb and drives superb. It really is hard to beat some of the iconic car designs of the sixties but who wants to drive around in a car that feels like an engineering museum piece when we have become so accustomed to the smoothness and comforts of modern driving.

Which Model Cobra

I’m hoping to achieve something similar for the Cobra, ie. a classic shape with a modern twist and under the bonnet a mighty V8 with far too much HP! The LS3 with a magnum 6 speed will be the perfect platform. Its still an American V8 with insane amounts of torque, the all-aluminium construction makes for a ridiculously lightweight package with a modern ecu allowing for switchable maps it can be as economical as a medium family car or as brutal as fully fledged drag racer.

Ok, that’s the kind of desire set down in words – now how to go about it? Of course it would be insane to do this to an original cobra (not that I could afford to) so a modern replica it has to be. That said, I dont feel that a modern tunnel chassis car weighing in at around 1ton and capable of 600hp (after IVA of course) will be too much of a compromise to suffer.

I did consider the other two main rivals in the UK Dax and AK and I can understand why they have a terrific following, there are after all some excellent examples around, but for me the GD design and quality of build is superior. GD may be slightly more expensive for the chassis and body parts but after that the really expensive bits for a high end build are pretty much the same whatever you buy and the difference in price by the time you get to the end becomes much less significant.

December 2015

Getting Started

Well It was on my Bucket List!

I have been planning to build a cobra for a very long time, eventually I decided I best be getting started. So here I am.

I have followed cobras and cobra replicas for many years I think I was buying kit car magazines back in the late 70’s so I certainly was not new to the idea. Last December My wife asked me what I wanted for Xmas and my stock answer has usually been …… (A cobra would be nice) but this time instead of the stock reply ( xxx ### ### xxx) she said well why don’t you get on with it and get one – I didn’t have to be told twice…..

Between Xmas and new year Andy at GD cars was kind enough to open up especially for us to come down and visit the showroom. I had already decided I was buying one so he didn’t have to do a hard sell. Before the visit I had already read enough to convince me that a GD was my first choice and nothing I seen or heard on that first visit changed my mind so I had placed my order before I left…

My Planned build.

I’m going with a modern take on a cobra rather than a traditional route, LS3 engine and no chrome or shiny metal in sight. I know it won’t be to everyone’s taste but….. (its my bucket list!)

Body Colour — choices – I really like the dark red metallic with fat billboard tyres aka the AK new demonstrator. Maybe a little too traditional though.

Plain Black on Andys demonstrator looks amazing!

Then there’s plain grey with red and black accents – my son (who will be helping with the build) prefers this one – so that’s what we are going with for now. I’m guessing I don’t have to finalise that decision right now as the body isn’t due until May.

I’m aiming at something like this LHD car — (all black wheels and black windscreen already on order!)

End of January 2016 I was kindly invited to meet Dale and Keith A, who were both fitting their body on the same day and only live just over an hours drive South from me. It was great to see their cars nearing completion, what a high standard they are both achieving. I was particularly impressed by the attention to detail both in the kit and the workmanship of Keith and Dale….. Thanks for inviting me down!

End of February 2016 – JUMP START

Well by luck or good fortune I was able to get a jump start and acquired a previous GD customers Chassis. He wasn’t able to progress for personal reasons and had not touched the chassis other than fit the brake lines so it’s a clean start and an eight-month time saving for me…

Early March 2016

First Job was to get all the rolling chassis bits together. Diff has been sent off to AllGears of Nottingham to recondition and de-rate – the hubs are off to Wards for refurb.

Both have promised me returns in about 3 weeks so that gives me a few weeks to find some Etype drive shafts and wishbones and get all the other parts ready to make the chassis Roll.

Nothing much else to do except wait…….but then again I’m already quite a bit ahead of time….so not complaining.