kind of a stupid question but was curious.
ive come across this many times now while searching craigslist and was kinda curious about it. is this just like a replacement for the gears in a lsd tranny or what? idk not really sure what it is

http://portland.craigslist.org/clc/pts/1141929664.html

 

A differential is the rear axel that changes the engine/driveshaft rotation to the correct direction to turn the wheels. This part will apparently replace the center section of some Rx-7 differential with a limited slip unit that sends power to both wheels instead of just one. Some Rx-7s came with a lsd stock. Some did not. It would not fit all Rx-7's. You would have to check with the seller to find out what specific application he bought it for. Some lsd's can be found new for near that same price.