Brother HL-4040CN Service Manual page 209

(4) Remove the two cup S M3x6 Taptite screws, and then remove the Drum drive motor 1.
(5) Remove the two cup S M3x6 Taptite screws, and then remove the Drum drive motor 2.
Drum drive motor 2
Taptite, cup S M3x6
Assembling Note:
The two Gears 39/121 which are engaged with the same motor are phased with each other
when assembling the Drum drive ASSY. If removing the motor to replace it, the gears may
be out of phase. When replacing the motor, therefore, be sure to phase the Gears 39/121,
and then assemble the motor. For the method how to phase the gears, refer to the figure
below (Fig. 3-147).
Align the mark on the Gear
with the line on the Drum
drive plate.
Drum drive motor 1
Taptite, cup S M3x6
Fig. 3-146
Drum drive ASSY
Gears 39/121
Align the mark on the Gear with
the space between the two lines
on the Drum drive plate.
Fig. 3-147
3-101
Frame unit
<Left side>
Gears 39/121
Confidential