Hello ! I've been trying to fix this machine for a while now. I've just replaced the gearcase assembly and I cant get rid of the f7 e8 code. The drum spins freely and the motor is not overheated. Could it be a motherboard or sensor problem? Thanks so much in advance

It sounds to me like the motor is bad. It's overheating and throwing the internal overload on the motor causing the F7E8 error which means the motor is overheating.