The spur gear wasn't too bad. Just need the pinion closer. Use a piece of paper in between the gears to get the mesh correct.
I regeared the axles and did a lower gears in the transmission as well with a stronger motor. I can't remember which parts and what ratios but it's very crawly and powerful. Not fast but tons of torque... more control. My son's out runs mine but I can crawl a lot better