Rear end side gears

Recently I came across an early (81-83) small axle rebuilt rear end but my car is an 85. Can I just take apart the early rear end and put in 84-85 large axle side gears? Are the side gears the same for both early and late except for the difference in axle spline size? I realize that I will have to reset up the rear end and take measurements after the swap. Is it also possible to use the side gears from an open late model diff? I'm only planning to swap out the pumpkin not the whole rear end assembly. My current rear end is an 85 GSL model not an GSL-SE.

Well I pulled an open diff out of my pile of rear ends and decided to take it apart. It took about 5 minutes to totally disassemble and determine that you cannot use an open diff side gear is a LSD application. An open diff side gear has smooth shoulders where as an LSD side gear has grooves in the shoulder to engage the clutch discs. Now I need to take apart a late model LSD to see if the side gears can be installed into the early LSD.

Side gears from the second gen RX7 factory LS will work. Main difference in the two units is the ID of the axle hole in the casting. We used to sleeve the 1st gen units to use in the second gen.

No, I do not have any I am willing to sell.

Keep us posted with what you learn. I am really amazed no one on here knows the answer. Also don’t throw away that small bearing housing. Housings are getting harder to find (assuming it is disc brake) and one of us around hear seems to bend one up every year or so.

If the diff is broken you can get a 94 to 97 Miata torsen diff and swap the ring gear to the diff unit. Much better setup than the clutch type and they are readily available