Originally Posted by iKliiu
Battery is 8.4v, and it was fully charged. The motor was connected properly, and spun freely, just not when put inside the gearbox. The spring is under M120, like probably a M100 or M110.
Sorry if this is wasting your time, but I did not really see an answer to the correct wiring question. Above, you state that the motor "spun freely" but I never saw you state that you made sure of the polarity of the wiring. I just skimmed the thread, but never noticed this. The motor will spin freely, but backwards if the polarity is reversed. The anti-reversal latch will prevent anything from turning and the gearbox will appear "locked".
Ensure your motor's polarity before you tear down too much.