Hi im new here but not to rotaries lol. Ive been searching the web for answers but no clear answer was found. Can i use a lsd from a FC in a 85 gslse rear housing and get a 3rd member from another car, sporatage for example? Mazdatrix website leads me to believe this.

 

The fc Non turbo diff fits.

 

NA FC and Miata diffs bolt in, currently running a torsen in mine right now

 

I'm running a Miata Torsen, too. I like it a lot.

 

All 7" differentials interchange into an FB, provided that the axle spline count is the same, EXCEPT for the VLSD used in some FCs. (FB diffs may not interchange into IRS rears because of circlip groove requirements) If you have an '84-85 rearend, this means you can use any non-VLSD FC diff, or '94-up Miata diff. But not any Honda S2000 diff because they had a much bigger axle spline.

Go to Solomiata and look into the Drivetrain page.

Yes it is technically a Miata site, but Miatas are the true 2nd-gen RX-7s. They are more like 1st-gens than FCs, mechanically. And anyway, a LOT of the information there is Mazda-generic.

FWIW, my FB currently has a GSL axle housing, GSL-SE axles, and a complete untouched Kia pumpkin including the open diff...