This is a 3D printable (most of it) gearbox for your MrCrawley RC Crawler Chassis, and probably / maybe it will also work in your SCX10 chassis. The pitch and number of teeth for each gear is the same one than in the original gearbox, but there is no compatibility between them, in terms of replacing the gears or the case with the original ones.

The only "difficult" part is that you will need a 5x47mm metal axle and you will have to "metal-smith" it a little so it is finally useful. That means making some plain surfaces in the extremes of the shaft, so you can fix there the Universal Shafts extremes with their grub. The depth of those planes should be around 13mm on each side.

There is also another version of the output gear in which you fix the metal axle to the gear and its printed axle in the centre of the metal axle, through the gear with some M3 grub screws. That means the teeth of the gear won't be perfect, but you will get a more similar to original gearbox output gear. The length of the 5mm diameter metal part in this case would be 35mm.

The skidplate of MrCrawley is ready for the M2.5 screws that original gearbox uses, so if you want to use this printed version instead, you will need to increase to 3mm the wide of the holes in the skidplate to really be able to use the M3 screws to fix the gearbox to the skidplate.

About the gears, you will find a 32p 56T crown, 48p 20T gear sharing axle with the crown, 48p 28T idle gear and 48p 52T output gear... This should achieve similar reduction to the original gearbox. You should be able to use 32p motor pinions from 12T to 20T; I included the 15T one for you to try.

I have tested it with slow-mo but also full throttling my 2600kv sensored motor, which doesn't result in a great speed, but the gears seem to resist the acceleration. The sound and accuracy of my printed gears could be improved a little, but I consider they are working fine, even printed in PLA as they are.

List of screws and sourced parts needed

SH means Socket Head Screw
BH means Button Head Screw
CS means Counter-Sunk Screw
GS means grub screw