11 September 2021

LEGO® Technic review: 42131 Cat D11T Bulldozer

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Alexandre Campos kicks off a series of LEGO® Technic reviews that we will publish for you every Saturday for the next few weeks. Officially revealed yesterday, 42131 Cat D11T Bulldozer is released 1 October 2021 priced US$449.99/ AU$$749.99/ £419.99/ 449,99 €. Buying this set? Consider using our affiliate links, New Elementary may get a commission: USA LEGO Shop | Australia LEGO Shop | UK LEGO Shop/ for Europe 'Change region'. Products in this article were provided by LEGO; the author's opinions are their own.

Remember 42028, the bulldozer from 2014? Well, it grew up quite a bit in the last seven years, and mastered some new skills. Unfortunately, it also picked up a license from Caterpillar, usually known as Cat. Why do I say unfortunately? Well...

New Moulds

After all the moulds introduced in this year's Technic sets, there wasn't much room for more here. But look what the Cat dragged in.

The set uses 116 of these in Yellow (6321711|69910). It's a new, wider version of Technic Link Tread Wide with Two Pin Holes, Reinforced (88323). I'm not a big fan of absolute designations like "small", "wide" or "new": there's always the possibility of something smaller, wider or newer to appear, and this is the case here.

Anyhow, the previous version, which debuted in 2007 and is quite a popular choice for tracked LEGO vehicles, and even out-of-the-box stuff like decorations and trap bridges, is 5 modules wide whereas the new mould is 7 modules wide. So, I'd venture suggesting this piece be called "Technic Link Tread 7 with Two Pin Holes"?

For comparison, here are the three current types of LEGO tread links (there are some older ones, but they were discontinued long ago). As you can see, the 5L and 7L links have the same building interfaces: two half-depth pin holes, and clips to connect to each other and to the "large tooth" sprocket wheels.

Having the same interconnecting clips as the 5L tread links, these can be used to make "tyres" around the same wheels. With the cleats and the increased width, these remind me of Mars rover wheels. If we get these in grey (and I don't doubt we will), the appearance will be further strengthened.

Similarly to the 5L tread link, the half-depth pin holes in the new part mean we can mount stuff on it, either directly or via half- or ¾-pins. Given all the width available, I'd have liked to have an extra pin hole on each side, for more connection possibilities and the added bonus of requiring less plastic and therefore weighing less.

Unlike the previous version, this one has a highly protruding "cleat" that may help with traction in dirt or carpets. This cleat is exactly one tile high, and means that the Rubber Technic Tread Attachment (24375) doesn't protrude enough to be useful for adding grip for smooth floors.

As you may expect, it's possible to have these links connected "inside out". Forcing the parts as little as I could, I made this circumference with approximately 36 studs in diameter. You may easily make a smaller circumference that doesn't get squashed as much under its weight, if you're willing to force the parts a bit. It's only a matter of time before we see this arrangement in GBC modules.

With large sprockets and wide links, it's easier than ever for the track to tilt sideways more than desired. To avoid this, you might want to add wheels that directly touch the inner surface of the link on either side.

The 5L and 7L links can be mixed together at will. With different colours, I totally see this spiky look appearing in a Ninjago vehicle sooner or later. In these colours, you just need to add a trans-yellow canopy and some trans-red guns, and you get a Blacktron I tank.

I almost forgot... there's another difference between the 5L and 7L link, besides the width and cleat: the material. While the older version is made of the hard "standard LEGO plastic", the new version appears to be made of a slightly softer compound, comparable to LEGO plastic wheels. This should allow for less sliding and noise on smooth floors, but increased wear, especially concentrated on that protruding cleat. The currently available colour, yellow, also means any dirt and grime will make it ugly in no time.

The necessity for wider tread links probably appeared when the LEGO designers concluded they'd need to better spread the weight of larger and heavier Cat models.

Parts in new colours

While the set has "just" one new mould. it brings us a few existing ones in new colours.

The first of these is the Technic Gear Rack 1 x 14 x 2 Housing, in Dark Bluish Gray (18940 | 6328090). This neutral colour should make it versatile for builds of diverse colours.

Going the opposite route from a more versatile to a more specialised colour, we get two parts in Yellow: Technic Beam Frame 5 x 7 Open Center Thick (64179 | 6352947) and Technic Beam 1 x 5 Thin with Axle Holes on Ends (11478 | 6371968). The set gives us 4 of the former, and a whopping 35 of the latter.

I'm not sure whether to consider the black linear actuator just a new colour or a whole new mould. It has the same dimensions, attachment points and range of motion as the grey versions, but the two halves of its outer shell join together in a very different way, which suggests changes in the internal mechanism. I couldn't find any Design ID (no, it's not moulded in the same place as the grey actuator), so I'm tentatively assigning it "61927c". Its Element ID is 6368625, and the Cat presents us with 6 of these. Oh, and going with the Powered Up's trend of red accents instead of Power Functions' orange, the colour in this actuator's axle hole was also changed to red.

Other parts of interest

Here are some other interesting parts that come in the D11T. These parts are present in very few other sets or have been absent for a long time: 

  • 6 x Technic Tread Sprocket Wheel Large Diameter 7 Holes in Yellow (42529 | 6253463), present in 1 other set;
  • 2 x Technic Panel Fairing #21 Very Small Smooth, Side B in Yellow (11946 | 6352653), present in 2 other sets;
  • 2 x Technic Panel Fairing #22 Very Small Smooth, Side A in Yellow (11947 | 6352686), present in 3 other sets;
  • 2 x Technic Steering Arm 5 x 1 with Towball Socket (Type2) in Yellow (31794 | 6345163), present in 1 other set;
  • 2 x Wheel Hub with Planetary Gear Reduction in Light Bluish Gray (46490 | 6365803), present in 2 other sets;
  • 15 x Technic Panel 3 x 7 x 1 in Yellow (71709 | 6334490), present in 2 other sets;
  • 6 x Technic Beam 2 x 3 L-Shape with Quarter Ellipse Thick in Yellow (71708 | 6332412) , present in 1 other set;
  • 1 x Wheel 31 x 15 Technic in Yellow (60208 | 6363273), for the first time since 2015;
  • 2 x CV Ball Joint Female in Dark Bluish Gray (52730 | 6261793), present in 3 other sets;
  • 2 x Brick Round 1 x 1 diameter Tube with 45 Degree Elbow(2 x 2 x 1) and Axle Holes(Crossholes) at each end in Black (65473 | 6305216), present in 1 other set;
  • 6 x Technic Panel 5 x 11 x 1 Tapered in Yellow (18945 | 6310998), present in 3 other sets;
  • 4 x Technic Panel Curved 11 x 3 with 10 Pin Holes through Panel Surface in Yellow (11954 | 6251202), present in 2 other sets.

Another uncommon part is Motor, Large Angular Position, Light Bluish Gray Housing, Black Wire in Dark Bluish Gray (69730 | 6317490). It previously only appeared in one set, and the D11T makes good use of the motor's double-sided, perpendicular output. Dear TLG, if you're reading this (and if you read NE, you have very good taste), I have two suggestions regarding it.

This motor, originally created for MINDSTORMS, has markings on its case that denote the absolute zero position. This is very useful when building and often makes programming easier. So, I'd like the Technic-derived motors (Motor, Large, Powered Up 22169 and Motor, XL, Powered Up 22172), which also have absolute positioning, to have similar external markings.

Also, what's with "MOTOR, NO. 15"? That name certainly doesn't roll off the consumer's tongue. Could you please give it a more intuitive name? You can use Rebrickable for inspiration.

"Flip-flop beams" appeared this year and are becoming more common as designers notice the huge potential they present. The Cat comes with a generous serving of the two currently available flavours:

  • 22 x Technic Beam 1 x 11 Thick with Alternating Holes in Black (73507 | 6330585)
  • 18 x Technic Beam 1 x 15 Thick with Alternating Holes in Black (71710 | 6321716)

I found something odd in the parts inventory at the end of the instructions: it mentions both 2nd-gen (2780, in the middle in the photo) and 3rd-gen (61332, on the right in the photo) friction pins, but the review copy I got only contains the latter. Could the instructions have been printed during the transition phase from old to new, and some copies of the set come with mixed types?

Sticker sheet

42131 comes with a moderately-sized instructions sheet. It comes packaged with the phonebook-sized (for the young ones out there, a phonebook is a really thick book) instructions books, so it's protected against the assault of parts bags tumbling around.

Fortunately, the model doesn't require any stickers to look good, and there aren't any printed parts that could make your MOC life harder.


As mentioned earlier, the instruction books are really large, enough to stuff a few litter boxes.

As you may expect from an 18+ set, there are a few pages dedicated to the real thing and design process of its LEGO version. These are very appreciated. Of note is this photo of an early prototype version, that features white/azure motors from SPIKE Prime and the older 5L tread links.

Regrettably absent from the books is this photo of a later prototype. As you can see, it's already very close to the final product, with all the Cat branding present.

Building the set

The building process is divided in eight numbered sections. According to the instructions, they roughly correspond to the assembly of the real D11T, which is so large that it needs to be transported in modules to its work location.

This is the drivetrain that powers one of the treads. The angular motor connects directly to the planetary gear hub, to which the sprocket is attached. While the mechanism itself is simple, the structure that supports it is not, due to the hub being designed to be part of a car's suspension. Given the usefulness of a compact planetary gear reduction, I suspect we'll see in the future a version of this part with more generic attachment points and the ability to have a regular axle as input instead of a large CV joint.

I found this step a bit challenging: it required me to add a yellow Technic Beam 3 x 5 Thick (14720 , also known as "dog bone" at TLG) inside this assembly, attaching it to four pins at once. I managed to do it, but not before some finagling.

After putting this assembly together, I felt like having just practiced some sort of black magic: the Technic Axle and Pin Connector Block 4 x 3 x 2 1/2 (61904) ends up at a really weird angle relatively to the yellow and black beams, yet the construction is rock-solid and doesn't force any connections.

Apart from the notes above and the obvious repetitiveness of assembling dozens of tread links, the only issue with building I had was handling the Cat's ever-increasing heft. I really must start feeding it less, no matter how much it meows for food. The construction process was, in general, very enjoyable.

Finally, I don't usually mention the spare parts, as they're usually tiny elements LEGO gives you in case you lose one and you probably already have heaps of these. However, in this case, we get two whole extra tread links. Perhaps the Technic team was thinking "hey, we're done creating the set but we still have this budget left, let's throw in more of this new part". And I'm very glad they did that.

The completed model

Now that the D11T is out of the bag, or in this case box, it's time to analyse it as a whole.

This is an imposing and chunky machine. It feels satisfyingly heavy and solid, with only some details like the air filters and other brick-build gizmos in any danger of popping off.

Opening the side doors of the engine compartment, we can see the V12 that makes the Cat purr. The engine is connected via differential to the two treads, which makes it run at full speed when going forwards or backwards, half speed when one of the treads is stopped, and stopped when turning in place. I love all the System- and Technic-built details, even though they're not needed for play and are hidden most of the time.

The red lever below the cylinders is there to help you press the button that powers on the Control+ hub. The hub is buried deep within the D11T, so turning it on would otherwise require some dexterity and skinny fingers.

Fear not though, for as while the hub's button is hard to reach, its batteries can be easily swapped. You "just" have to turn the model upside down (or at least lie it on its side) and pop open the battery compartment. Since this is a single-hub set, it just takes 6 AA batteries.

Still looking at the Cat's belly, more towards the rear we can see the main gearbox that distributes power to four of the functions, and the differential that takes power from the propulsion motors to the V12 engine.

The cabin can be accessed from an opening door on each side. There's plenty of stuff for the operator to operate, and I found the detail of the seat being slightly oriented to the side interesting. I don't know what's the purpose of that, but that must be a feature of the real deal so I'm happy to see it here. I'm also glad to report that this set is techfig-scale.

When you turn the black 12T gear at the bottom of the photo, the front sprocket moves longitudinally. This increases or decreases the tension in the tread, and is a first in official LEGO Technic; too little and the tread flops and can jump out of the sprockets, too much and the motor has trouble overcoming all that friction.

Each tread has its own independent tension mechanism. Since they're built equally and therefore require the same tension, there's no reason to have to adjust them individually. As you can see on the photo above, there might be room inside the model to mechanically link the two mechanisms.

The set's meat-and-potatoes is unquestionably the remote control. A Hub, Powered Up 4-Port (22127) functions as the Cat's brains. Two Motors, Large Angular Position (69730) drive the treads directly (and, as stated above, jointly drive the cylinder engine), and two Motors, Large, Powered Up (22169) take care of the other 4 functions. One of them drives the mechanisms, and the other selects which of those are powered.

As of writing this, the Control+ app hasn't been updated with a profile for 42131, so officially you can't do anything with the set besides admiring the engine, opening the doors, and adjusting the tread tension. Since I don't like on-screen controls anyway, I intend to program the hub with Pybricks to be able to drive it with a standard LEGO Powered Up controller.

One of the four selectable functions is raising and lowering the front blade. All LEGO Technic bulldozers have this, and it wouldn't be a LEGO bulldozer, especially at this scale, without it.

On the other hand, tilting the blade is a first amongst official Technic bulldozers. This is a complex mechanism that branches off from the main gearbox to both sides over many gears, yet it has surprisingly small backlash.

The rear ripper can be raised and lowered, but, unlike the rears of other cats, you can't do it by scratching its back; you need to use the motors. Real bulldozers can both raise and tilt their rippers, but in this set the latter function is simulated by brick-built "linear actuators".

The final motorised function is a deployable ladder. Its motion is very interesting to see, when it shifts from being longitudinally stored alongside the body to coming down along the side of the vehicle. I bet it took a lot of effort to develop and fine-tune the required angles to do this so elegantly.

The B-model

Move along, nothing to see here.

This is the third-and-a-half year in a row (I consider the 42082 Rough Terrain Crane to have half a B-model) that we get a cold shoulder when asking for a flagship set's B-model, and I'm afraid this trend is here to stay.


This is not a cheap set: EUR 449.99/ USD 449.99/ GBP 419.99. Many people have been comparing it with 42100 Liebherr R 9800, which costs the same, yet has an extra Control+ hub and 3 motors, and its linear actuators are of the longer variety. I don't think inflation can explain this in a significant capacity, as it's not been that long from 2019 to 2021. Let's see how the D11T holds up, then?

The Cat sure feels like a powerful beast. From what I was able to test, its functions work well, even if a bit slowly. It has interesting parts, including the large angular motors, the several moulds in yellow, and especially the new tread links. However, the Liebherr also is powerful and works well. On top of that, since it can have all its functions work simultaneously, it has no problem doing the moves you can program in the app. Being able to do just one thing at a time (besides moving), the Cat just isn't as enjoyable to play with.

Putting the R 9800 aside, the price does seem excessive for the D11T: for what it brings to the table, I think maybe less 150 of your favourite currency would be a lot fairer. As I wrote earlier, it does have interesting parts and building techniques, but costs just too much to justify them.

If you're hungry for raw material for MOCs and are on the fence between getting 42100 or 42131, I'd definitely recommend the former. It gives you more bang for your buck, and shouldn't take long to retire. Then you'll have more time to adopt the Cat later, hopefully when it's discounted.

These two cats may look the same, but in reality they're not. Can you find the 10 differences?

READ MORE: LEGO® Ideas 21329 Fender® Stratocaster™reviewed, including a new inverted curved slope

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  1. In the one pic, the cat looks visibly annoyed that you are 'treading' on it.

    1. Not cats were harmd during this review. The cats did harm some people that tried to make pictures of them ;-)

  2. I might not be the only one, but I get a lot more jealous on you owning all these Lego cats than the actual Caterpillar...

    1. It was a tough job herding them all into the picture, but someone had to do it...

  3. The new wide links certainly look a lot better on a model this big, I hope we see them in gray or black (and on something less expensive). They'd work well on a smaller-scale snow groomer for example.