"Houston, we have a problem"... on the rear diff, at least. <img src="/forums/images/graemlins/zombie.gif" alt="" /> <img src="/forums/images/graemlins/zombie.gif" alt="" /> <img src="/forums/images/graemlins/zombie.gif" alt="" />


I went to a bone-yard yesterday to pick up a spare rear diff (26 spline), just so I could pull it apart to confirm or deny that the OBX diff spec'd for the Miata will fit. It won't. It turns out that, in the U.S. at least, the 26 spline rear diff with 7.5" ring gear IS DIFFERENT than the front diff with 7" ring gear. I haven't yet compared the front and rear diffs directly. But I did test the fit of the 7.5" ring gear and ABS ring (tone ring) against my OBX diffs (had to check both to convince myself that the results were true). They are - the 7.5" ring gear is larger than the mount and case on the OBX diff. <img src="/forums/images/graemlins/zombie.gif" alt="" /> <img src="/forums/images/graemlins/zombie.gif" alt="" /> <img src="/forums/images/graemlins/zombie.gif" alt="" />

I don't understand how anyone got the rear LSD of any Mazda RX-7/Miata diff to fit in the rear axle, unless they set it up with front ring gear and pinion. Is that even possible to do and still keep the proper gear ratio between front and rear axles??? <img src="/forums/images/graemlins/confused.gif" alt="" /><img src="/forums/images/graemlins/confused.gif" alt="" /><img src="/forums/images/graemlins/confused.gif" alt="" />

Here's a few photos to show you what I have found...


The OBX diff set on the 7.5" ring gear from the 26 spline diff...





A view of the offset hole pattern when one side is lined up... <img src="/forums/images/graemlins/scared.gif" alt="" />





ABS "tone" ring should be snug on the ring gear mount... not even close.





Ring gear set on the OBX case. It should be snug on the case-body... again, not even close. <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/scared.gif" alt="" />





So it looks like I'm "S.O.L." on getting the OBX diff in the rear. I could look into having the ring gear drilled for the smaller bolt-pattern and having spacers made to adapt the case for the ring gear and the ABS ring. But that will be a lot of $$$, if it would even work. So I'm going to look into other options for the rear axle. I'll let you know what I find, if I find anything. And I will let you know what comes of the front diff once I get into it... <img src="/forums/images/graemlins/confused.gif" alt="" /> <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/zombie.gif" alt="" />