Brother MFC640CW Service Manual page 154

(15) Remove the two screws and release the paper feed motor from the engine unit.
Engine unit
PF roller gear L
Screw, bind M3x3
Reassembling Note: When attaching the PF encoder disk to the PF roller gear, put on clean
gloves to protect the disk surface from dust or fingerprints.
To the PF sensor PCB
Paper feed motor
5 - 6 8
Paper feed roller
PF motor/sensor PCB
harness
Confidential