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The only place for a coil spring is up Zebedee's arse
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Hi all,

Thought I would share this project of mine with you all.

Since fitting the larger tyres to my P38 (235/85R16) the spare doesn't fit into it's usual spot anymore. This past December break I fitted the spare to the roof while we went on a little roadtrip here in SA. It worked, but isn't the ideal spot, mostly because I don't like the look and added wind resistance, but also because my windsurfing gear has to go up there in future. I started designing a spare wheel carrier for the rear in August last year and I've been spending a few hours on it here and there. This afternoon I just finalised the first design revision and sent the parts off for lasercutting. I'll document the build process here.

Spare location on the roof:
enter image description here

Proposed location on the rear:
enter image description here

I'd like to retain the original bumper in this first revision, additionally I'd also like to retain the ability to unbolt the major components and possibly update or change them in future. I'd like to minimize the amount of welding to the existing chassis also.

Overall view:
enter image description here

The carrier will attach and hinge on the chassis on the right rear corner. This will attach to the rear chassis longitudinal member here:
enter image description here

The chassis mount will be bolt on, with only holes drilled into the chassis, no welding. The bolt on plates will be supported on two planes and supported on the inside of the chassis with backing plates to support the load:
enter image description here
enter image description here

The standard bumper will cover all the modifications to the chassis (if I managed to measure correctly, if not, I'll have to make a plan on the fly) with only a hole in the bumper on the right hand side for the swingarm bolt to pass through, as well as holes for the fasteners where the center mount attaches to. The center mount will support the swingarm vertically in the closed position as well as supply a position for the closing clamp to attach to. The center mount attachment will be welded to the rear crossmember (round bar behind the spare wheel well and inside the rear bumper), which is removable and can thus be welded off vehicle.
Center mount attachment:
enter image description here

The swingarm assembly is supported by two deep groove ball bearings (replaceable) and is bolted to the chassis mount with a high tensile M20 bolt. The swingarm assembly will support the spare wheel as well as a mounting location for a high-lift jack.
Swingarm Assembly:
enter image description here

The center mount will bolt to the center mount attachment through the standard bumper and give the swingarm a pace to locate into and clamp onto:
enter image description here

Swingarm located into center mount:
enter image description here

The swingarm is has a secondary locking pin that locates into the chassis mount and this secondary locking pin will also lock the swingarm in it's open position, allowing normal operation of the tailgate.
Secondary locking pin and swingarm bearing assembly:
enter image description here

Hopefully I'll get the lasercut parts before the end of the month so that I can get going with the fabrication!

Cheers,
Justus

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Just tried to edit the post so the pictures appear but they seem to be private and not accessible to anyone other than the owner.

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I edited the album permissions. Are the pictures visible now?

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All except for the first one, the others are showing now.

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I can confirm the pictures are visible.
Impressive work JL. The engineering and thought that has gone into your project are first class. Drawings are excellent.
I look forward to seeing how the fabrication goes.

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Impressive work but if I was doing something like that I'd just modify tail board to open sideways

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erm ... I don't think it is that easy, Symes.
You are thinking of welding up the top and bottom half of the tailgate and fitting side hinges?
Structural work to support a side hinge door plus the weight of a spare wheel bouncing round off road would mean major reinforcing.

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Thanks for the kind words Dave!

I agree, converting to a swing arm door is going to be quite complicated and I do quite like the drop down tailgate.
Ultimately the swing arm will likely get a fold out table which will go nicely with a fridge slide on the left side of the boot area. It'll make for nice little camp kitchen setup I think.

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I said tail gate not top half and tailgate wouldn't need much reinforcement just look at discovery door

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That's what I was thinking, even the factory hinges on the Disco 1 droop. Admittedly that lower half is probably quite a bit lighter but I find the drop down tailgate to be very useful, it's a seat as well as a workbench.

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The top half of the tailgate has to lift up first to unlock. It would not clear the wheel with that arrangement, which would be mounted on the bottom.

I have also had a Discovery. The side opening door was a pain in the ass. I like the drop down tailgate, it is a lot more practical. I much prefer a p38.

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just looked at your pics very good , as for the swivel pin assembly most use a stub axle from a trailer for ease of assembly. (off the shelf component) just a thought .

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My only comment would be to look at offsetting it to one side or the other to improve your rear vision. Great work though!

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if you offset the rack you will block off your tail lights then you will have to put some form of lights in your rear bumper like in a pootrol . its a lot easier to move the number plate than the lights?
PS in Australia patrols have their lights in the bumper because the spare is on the back door and the visual for the rear brake is obscurer ed so they tell me , thats why the rear lights on most patrols dont work they dont even have holes to put the globes in , but you can buy them and simply plug them in.

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I like it a lot! Wait to see fab work and prototype ... keep track of costs and tooling you might have a winner for a (limited?) production series :-)

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Thanks for the positive comments!
We'll see how the final items turns out, this is probably the most complicated fabrication project that I've taken on. I've done some fabrication before (built a carport at my girlfriends place, as well as a rotisserie for a Fiat X1/9 and some other minor projects) but this is definitely the most intricate with a bunch of little parts that all need to work together correctly.

I am planning to offset the wheel to the right as far as it'll go without interfering with the RHS taillights as well as keeping the tailgate button within reach. Hopefully this leaves enough space on the left for another swingarm that can carry a jerry can or two in future. I'm getting ahead of myself though, let's first see if this works!

Pic showing the offset to the right:
enter image description here

I'm not really sure if a production run of something like this is worthwhile? Shipping something like this from South-Africa to the UK for example might be a bit pricey. Once I've verified the design and there is enough interest then making the design available for replication might be an option.

If the swivel assembly doesn't work out like planned then I'll go over to the trailer stub axle idea. The current solution is strong enough to carry the wheel, definitely in the closed position, but in the open position an adult climbing on the far end of the swingarm might deform the M20 bolt according to the maths. The trailer stub axle is quite a bit stronger, but is also larger and less elegant. I'll go with the design as is and then we'll see if it is an issue.

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One thing you might consider as Mad-as says is fabricating a special rear bumper which incorporates secondary rear lights in them. Phase 2 of the project.
It would allow you to move the wheel right over to the right and shorten back the arm. The canterlever forces would be less.
You could even have a second arm on the other side with a couple of jerry cans on it. They would both hinge outwards and lock together in the middle position. Unless you do something with the lights you couldn't do this.

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Very nice design. I'll be watching your progress.

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I got the lasercut parts just before the weekend and got going with the build.
My first feeling when receiving the bits was that they are quite small, it really is a bit tough to judge size on CAD.
I also struggled to get the correct size pipe for the bearing mount. I was looking for 57mm OD with 2mm wall and finally found a supplier. Got the pipe home, measured it and turns out they gave me 60mm-OD 2mm-wall. Dammit, should have measured it when I picked it up!

The major disadvantage with the bigger pipe is that it's harder to center the bearings, but the larger OD does mean that the load will be spread better through the rectangular tube of the swingam. Gave it a go and it turned out good:
enter image description here

Next I got the bumper off and started with the bolt on support for the bearing mount. It had to be shortened quite a bit and trimmed along the curve of the bumper too. I knew this might be required as it's a bit tough to accurately replicate the bumper shape etc on CAD (for my experience level anyway).

This:
enter image description here

bolted on here:
enter image description here

had to be shortened and trimmed:
enter image description here

and ended up like this:
enter image description here

The bumper fits tight over this bracket, but it does fit. Next step was to locate the bearing carrier and make the necessary holes for the M20 bolt to run through. You can see the location of the hole in the previous photo, circled in green on the bumper lying on the ground and a dimple on the forward piece of rectangular tube.

enter image description here

The M20 bolt will enter through the top smaller hole and bolt through into the M20 nut which is sunk into the rectangular tubes and welded to them.
enter image description here

Some spacers to space the bearing through the bumper and you end up with this:
enter image description here

Here you can see the bottom of the bolt screwed into the M20 nut which has to still be welded to the bolt on bracket:
enter image description here

And the back corner from outside:
enter image description here

I have deviated quite a bit from the original CAD model in terms of location of the bearing mount on the bumper (it's moved left and forward) but I expected needing to make some changes and I'm happy with the outcome. It's been fun spending the weekend welding and fettling and measuring, a nice break from the PC.

Happy Monday all!