If I put the old mac hard disk system drive with bootcamp in a USB caddy, after replacing it with an SSD, will it appear as 2 drives when plugged in

The answer:

I took the 1TB HGST Travelstar 7K1000 and gave it a firmware downgrade. HGST emailed me application to set the port to either, Sata I, II, or III. Reducing it to Sata II solves the problem.

No more dropping.

Has somethgn to do with Apple/intels first venture into the Sata III world back then. I used the less expensive Opti bay kit. Not the more expensive Extreme they have created to solve the problem.

Works great and is plenty fast for a seconday drive.

I just started having this exact same problem with my FreeAgent Go drive which has always been working perfectly. Like the original poster I cannot see the drive in Disk Utility but it does show up in System Information. After a little more digging I found that the OS is trying to repair the volume BEFORE letting Disk Utility see it via an process named "fsck_hfs". When I force quit that process in Activity Monitor (it's owned by Root so you'll need to give it permission), the volume immediately appeared in Disk Utility. I'm running a repair on it now - fingers crossed. My guess is that since this is formatted HFS+ Journaled something about the journal consistency got flagged and the OS is attempting to repair it from the journal. I'm shocked that they hide it from Disk Utility while it's happening though - much better would have been to display the drive there without mounting the partition, and display a message that this is being done. Oh well at least I can see why Windows would mount it but OSX won't now (any OSX machine would start performing the same repair process).