Using a Phillips #00 screwdriver, remove the four metal spacers (pegs) from the old HDD and install them in the same locations on the new HDD.

If the new HDD is thinner than the old HDD, you may need to unscrew the spacers a few turns to prevent the HDD from rattling around in the device.

Place the temperature sensor in approximately the same position on the new HDD as on the old HDD. Cover the sensor with the foam, using adhesive tape if necessary.

Make sure the surface of the sensor is flat against the metal hard drive enclosure.

To save power and reduce heat waste, use a "green" (power-saving) hard drive or a low-speed (5400 RPM) hard drive.

It is possible to test the device's functionality before fully reassembling it. To do so, reconnect the fan and replace the metal casing (without installing the screws).

To prevent electrical shock and overheating, complete this step before turning the device on.

After the Time Capsule is reassembled, format the new HDD using Airport Utility. It may be necessary to perform a hard reset on the Time Capsule.