Brother MFC640CW Service Manual page 66

When the head/carriage unit travels from the left to right to reach the purge position, a tab on the
carriage rear panel pushes the purge lever to the right (left in the illustration). The clutch gear spring
pushes the clutch gear to the right, away from idle gear L, to mesh with the purge gear. At the purge
position, therefore, the maintenance unit transmits the paper feed motor rotation to the bevel gear.
On the other hand, when the head/carriage unit moves left from the purge position, the tab on the
carriage rear panel releases the purge lever, allowing a spring to force the purge lever and the clutch
gear to the left. The purge lever spring is stronger, so forces the clutch gear spring back, disengaging
it from the purge gear.
PF roller gear L
Paper feed motor
(Front)
Pump switching unit
PF roller gear R
Idle gear L
Purge gear
Maintenance unit
Switching arm assembly
Confidential
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