Modified Lego Giant Truck 5571 and Highway Rig 5580

When I bought the Lego Model Team Giant Truck 5571 (also known as the Black Cat) back in 1996 I knew I’d modify it to give it a decent size sleeper cabin. The original is just too small for looks and comfort and I wanted something like a Kenworth W900 sleeper cabin.

I had disassembled and extended the chassis a little later by 8 studs but didn’t get around to finish it then and it ended up gathering dust on the shelf.
Until I had the opportunity.


Made the chassis 16 studs longer in total, at first 12 studs for the bigger cabin but after I finished the second variation I remembered to check the distance between dish and cabin, and it was too short for a trailer to turn, so at the third variation of the cabin I extended the chassis again.

At first I thought 12 would look longer than a regular cabin and more like a long customised truck, but it felt like the right, normal size soon. Making something like a long custom cabin would probably stress the chassis and front axle too much with the increased weight. Never mind the length it would get and where to keep the truck on display.

That’s why I don’t have any plans to build a trailer for it even though this long trailer looks nice if I make it wider and higher to fit the dimensions of my modified truck. And a (short) 20ft container trailer wouldn’t look right behind this one. For that I’d want a regular DAF 3600 Spacecab (without spoilers) or the truck of my own design.
Well, maybe a 40ft container trailer would look good.



The sleeper cabin is lengthened by 12 studs, widened by 4, and heigthened by about 3 block heights.

The first version I did wasn’t widened and it looked wrong enough together with the angle of the windows for me to disassemble and start from scratch, also to create a new low floor instead of the higher original one.


The second variation was wider by 2 studs and looked much better, but it still wasn’t quite good enough.
And I wanted to lengthen the chassis behind the cabin to fix the trailer issue.


The third cabin became the width of the fuel tanks, which were originally the only wide parts of the truck together with the front bumper.
At this point I needed to move the exhausts further outside as well to match the new width.
The increased length of the chassis was effective to add to the sense of a real truck.


The current version of the cabin is more of a tweaked third version with “rounded” corners at the window, modified bed, and a partial tile floor.
Additionally, I removed the slit from the black chassis boxes and moved them back to the original position in line with the back wall of the cabin because they looked less massive.



With the higher cabin height I could lift the bed and move it to the front to create a bit more detailed interior with a swiveling chair, a wash basin, storage, and shelves. Nothing fancy yet though.



The rear axles were weird with their partial detailed look and the simple technic axle at the wheel sides. And of course it needed at least a drive shaft to complete the look.

Because the chassis bends slightly under the weight of the truck, the second rear axle received hardly any load and all of the weight at the back ended up on the first axle.
To fix this I made two new axles and balanced them on swinging beams. They don’t have much clearance but enough for the couple of millimetre difference in heigth between chassis and each axle.
While turning the truck, all four wheels show equal signs of torsion instead of nothing at all.

I kept most of the original design on top but underneath they look a bit more real.
I also tried to make an axle drive the shaft but unfortunately I don’t have small enough gears for that to fit in.




While I was modifying the rear axles I decided to do the front one too because it looked as flimsy as the original rear axles.
Replaced the 10 stud wide components with double 6 ones and with a little experimentation got it working without changes to the gear position.
I didn’t check to be sure, but I think the front wheels turn at a larger angle now. Which the truck can certainly use at the increased length and resultant wider turning circle.

While I was busy on the front I added some interesting bricks to close the open gaps where the engine would be. In the original state you could see right through the truck underneath the fenders and that’s far from reality.

I had already moved (and replaced) the rear mud guards and flaps further to the side at the fuel tank’s width and used the components of the mud guard to widen the front fenders. The front bumper doesn’t look out of place now like some sort of shovel.

The whole truck became the same width along the entire length, with the exception of the steps up to the driver cabin which look better in their original position.


Last tweaks were adding a few more details like extra rear lights at the top of the cabin, a short stepladder to the rear on the left, a couple of warning arrows, a bit more bracing to stiffen the chassis at the coupling dish, a few different technical bits hung from the chassis, a hinged bullbar (so the hood could still open), and increasing the spoiler size because it was just too small compared to the rest.
The roo bar isn’t pretty, but when I removed it, the front of the truck looked rather bare so I attached it again.






The large black and slightly lower boxes work really well to add a sense of weight to the rear. Moving them forward just one stud made the effect seem less. Unfortunately I don’t have the parts for it, otherwise I could have made real storage boxes.

Dual tyres on the drive axles would have been nice but these tyres are too wide in proportion compared to real ones used in a dual setup. I’ll just think of it as a (not quite) super wide tyre configuration option for truck buyers.



With all this done I can look at the model and really think this is indeed a giant truck. There is a sense of presence that was lacking in the original.
The looks match more that of a real truck and the model lost a little bit of the toy truck feeling compared to the original.



A search on who else modified the sleeper cabin only gave me one result:
Looks like this modification is pretty unique then.

Some data:
Length: 62cm (including bullbar it’s 64 cm)
Heigth: 21cm (sleeper cabin roof, including exhaust, antennas, spoiler it’s 26cm)
Width: 14.5 cm (exluding the side lights and steps, including mirrors it’s 17 cm)
Turning circle: 155cm
Weight: ~2.2kg (load front axle ~1.2kg, rear axles ~0.5kg each)
Wheel base: 43.5cm (front axle to centre between rear axles)
Centre of gravity: ~19cm behind front axle, ~1 stud behind centre of fuel tank.
Extra parts used: ~200 (estimation)









Of course I also owned the Highway Rig 5580 and had modified it into a longer tow truck with a second steering axle, with a towed deeploader trailer for a helicopter, which also featured a steering axle at the rear tandem. That version had been disassembled over time but when I rebuilt the truck again I kept it as a tractor and instead added a B-train combination with the helicopter trailer from the Whirl and Wheel Super Truck set 5590 that I received in a collection of Lego parts.

I made the same basic modifications as I did with the 5571, extended the chassis, widened the whole truck by two studs, enlarged the sleeper cabin, replaced the rear tandem setup, and added a few accessories.
I kept the helicopter trailer mostly original and replaced the fixed tandem axles with a swinging setup as well. I might replace it with a deeploader trailer some time in the future and improve the B-train trailer as well, making it even longer than the nearly 110cm it is now.







About SciFurz

Science fiction, fantasy, furry, horror stories, drawings and ideas, tech ramblings
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