Lenovo ThinkCentre 3656 Hardware Maintenance Manual page 113

3. The rear fan assembly is mounted with four rubber mounts that protrude
through the rear of the chassis. Remove the fan assembly by pulling the rubber
mounts back through the chassis.
4. Install the new rear fan assembly by aligning the rubber mounts of the system
fan assembly with the holes on the chassis and push the rubber mounts
through the holes.
Chapter 8. Replacing FRUs - Tamdhu Computers
107