Dell Precision T7400 (Late 2007) - Manual (Page 262)

262 Adding and Replacing Parts
7 If an empty 3.5-inch drive carrier is installed in the drive bay, slide the
Media Card Reader into the drive carrier until it clicks into place.
Otherwise:
a Slide the Media Card Reader into the 3.5-inch drive carrier until it
clicks into place.
b Then, while pressing down the release lever on the side of the drive
carrier, slide the drive carrier into the drive bay until it clicks into
place.
1 Media Card Reader 2 screws (4)
1
2