I recently needed to replace the SA1000 hard drive bubble in a Tandy Radio Shack TRS-80 8 MB Hard Disk Drive unit. While I was very familiar with how to do this in one of the later 5 MB or 12 MB hard drives,
I had never attempted the procedure on the 8 MB drive. In the end, it was fairly straightforward to replace the bubble, except for dealing with the famous Tandy 3 Wire setup. The 3 Wire Fix has been documented in the past by Roy T. Beck and Ian Mavric for the smaller 5 MB and later drives, but not for the 8 MB unit. Here it is for those handful of you out there running 8 MB drive setups.

http://pski.net/trs-80-8-mb-hard-drive-three-wire-fix/