I have a fully completed Cat D11. Great build. (I have previously built the Bucket Wheel Excavator, the Rough Terrain Crane, Liebherr 9800, Airbus 175, etc.) Couldn't get through calibration. Did not understand I should have tested the build per step 198. (You'd think I could follow picture instructions at age 74...)

Picture of step 198 showing an instruction to test the functions using the app

After much evaluation and checking everything I could think of, I can see in the build step 104 I put the small bevel gear ON THE WRONG SIDE of the drive gear. Obviously it is trying to drive that shaft in the wrong direction!

Pictures of steps 104 and 105, showing the misplaced bevel gear and its place in the larger sub-assembly

Does anyone have an idea how I can switch out the gear WITHOUT tearing the build down completely? I'd like to see my 75th birthday...

  • 1
    I'm afraid the only option is to go back to step you completed incorrectly to fix the issue. Bevel gears are tricky ones and unfortunately it got you unprepared.
    – Alex
    Apr 1, 2023 at 21:03

1 Answer 1


In Step 164 the axle the bevel gear is on becomes locked. At this step the sub assembly gets put on the main assembly and the axle is blocked by a large technic motor. Before this step, you could probably still manipulate the axle enough studs out with pliers to switch the bevel gear.

enter image description here

That's of course still lot of steps to reverse, but you'll notice that the entire model is built in lots of smaller sub-assemblies... so you don't need to revert each step, you can leave the sub-assemblies intact...

Alternatively, there are other ways to control the technic model than the standard app:

  • brickcontroller2: you could create a profile very similar looking to the control+ interface but arrange the responding actions to accommodating for the inverted bevel gear.
  • pybricks: You could create a program in python that controls the model based on input from a remote control or e.g. a PS4 controller...
  • powered up app: similar to brickcontroller2 but the "official" way Lego suggests to go if the Control+ app doesn't suffice anymore...

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