The Western Digital Dual-Option USB enclosures are handy devices for carrying data (high throughput sneakernet) or just for making offline backups of your data.
Eventually you might realize that you're running low on capacity, or your drive might die. Western Digital would prefer that you just buy another USB drive, but I'd rather reuse the existing hardware, especially since I have a few larger PATA drives sitting around now. This instructable gives you a play by play on opening the enclosure without breaking it (well, hopefully you won't break it because I'll show you how).
Step 1: Remove the Sides
This is the most difficult step and the one that is most likely to end in broken plastic.
Pry up the rear end of one of the long silver sides.
Slide the side toward the back of the drive. On my drive it was very difficult. I found that I was able to get things to move by standing the drive on one side and applying downward pressure on the side that I was trying to slide. This relieves some of the stress on the tabs that hold the side in place. Keep trying and be patient, or else you may end up with some broken tabs (like I did, on my first try).
Repeat for the other side.
Remove silver front. After prying up both sides I used my thumbs to wiggle it out.
Step 3: Remove the Top
Using a couple of screwdrivers, pry the dark top off of the bottom. There are eight tabs that hold the top to the bottom.
Step 4: Remove All Fasteners
Remove the silver tape and the three screws in the base. Lift the drive assembly out of the base and remove the four screws from the bottom of the drive. Disconnect the drive power and data connectors from the USB interface. You might want to prop the drive assembly up on the base like I did in the picture, because otherwise you have to disconnect the HID (front buttons) wire. Remove the six screws from the sides of the drive and remove the heat sinks.
Step 5: Install Your New Drive, and Reverse the Steps
From here on out it's easy. Connect your new drive and reverse all of the previous steps. You could even do what I did and install a Maxtor drive in a Western Digital enclosure. The world might just end.
You should test that everything works after reconnecting the drive, before you go and put it all back together. I found that my drive would not be recognized when the jumper was set to master. By setting it to Cable Select everything worked fine. This is probably a function of how flaky the USB interface is, so YMMV.