Hello, about 2 years ago I posted this same method to convert a 5 wire unipolar stepper to a 4 wire bipolar stepper. howto modify a xxBJY stepper motor
one thing that can happen if you are not very carefull on removing the cover of the wires one or more of these hair thin coilwires get cut and the motor is dead. On trying to connect and operate the motor this specific effect of vibrate but not move can result from a cutted coil.