Quirole

Hello from France, Did you find a solution please? Here my son has EXACTLY the same problem, he just had this toy for Xmas and he is very disappointed as he was so happy to finish the assembly. Everything works fine except wheels. Posting a video is useless as it would be exactly the same symptoms as MariusNO's.: to me, this red differential is a weird system: it moves correctly front wheels, but it is not efficient to move the rear driveshaft, it spins sluggishly, and once the wheels are on the ground, rear wheels spin the opposite way so the truck doesn't move at all... I tried Doug's advice but it doesn't help. All gears, bars, shafts and axles seem to move softly, no abnormal friction... My only temporary idea is to completely remove the rear driveshaft It seems it is a design problem of this model? Should I return this to the Lego factory? Thank you for you ideas Mitch