Brother MFC5100C Service Manual page 32

During printing: The ASF-purge switching gear 23 is
not engaged with purge bevel gear A (but engaged with
gear 25 in the ASF gear train).
When the motor rotation is transmitted to the purge unit, its counterclockwise rotation will drive
the purge cam and its clockwise rotation, the pump switching unit (when viewed from the output
gear of the motor).
When the paper feed motor rotates counterclockwise
When the paper feed motor rotates clockwise
3 -1 2
During purging: The ASF-purge
switching gear 23 is engaged with
purge bevel gear A.