Yes, there are different part numbers for the Eaton-Sporty LSDs.

93-97: #19519
98-09: #19536

Eaton LSDs for Sporty's on eBay

Hope that helps... <img src="/forums/images/graemlins/kewl.gif" alt="" />

"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="" />

"Dear Diary"... I stopped by the local 4x4 shop (where I bought my Smittybilt bumpers) and had a chat with the boys about my dilemma with the rear diff... and how I've painted myself into a corner... and that I'm determined to make something work, even if I have to stand on one foot while the paint dries - so I can switch to the other foot and finish the job! <img src="/forums/images/graemlins/shiner.gif" alt="" /> And from my discussion, I've narrowed down a few options...

A) See if the Lock Right locker for the Ford/Mazda 7.5" open diff is compatible with the 28-spline Sporty axles. The guys are having the part shipped in tomorrow morning and I'll stop by with the stock diff and a 28-spline axle for a test-fit. I doubt this will work because the Ford splines are reported to be 1.2" diameter, which is just over 30 mm. The Kia splines are 29 mm. And then the side-to-side spacing inside of the carrier would have to match too. But it's worth a try...

Estimated cost: $400

B) Had a desperation-induced epiphany at yesterday: The OBX diff is a 2-piece case. The only dimensional-difference between the stock rear-diff and the Miata-spec'd diff is the size of the ring gear mount (mounting flange and case diameter where the inside of the ring press-fits). The bearings are the same and the end-spacing is dead-on. So... I could have the ring gear-side of the OBX casing duplicated with the case diameter and ring mount modded to fit the 7.5" ring gear (i.e. have a new part machined). That would allow me to use the OBX gears + the other half of the case. I know that will work, as long as the machining is good... or at least as good as the Chinese-version of "quality control". <img src="/forums/images/graemlins/zombie.gif" alt="" />

Estimated cost: Unknown

C) Buy an Eaton LSD for made for the Sporty. The guys at the shop are looking into it and said they'd sell it to me at cost if they can find one. Their supplier said the 28-spline Eaton LSD (#19536-010) is still active in their parts-system, even though Eaton has discontinued them. They also said that if the "Just Differentials"-dude on eBay can get them, they shouldn't have a problem (they used more colorful phrasing while stating that... <img src="/forums/images/graemlins/notooth.gif" alt="" />). They also said the Eaton clutch-type LSDs are pretty solid and would probably last longer than I'll abuse the vehicle, as long as I don't spin a wheel in the air and slam it down on the ground (tends to destroy the clutches, they say). Again, another option that will work if the part can be found.

Estimated cost: Less than $699...

D) Try to get a Track Finder locker made for the 28-spline open carrier. That will work, for sure. But I haven't heard of anyone getting one shipped to the U.S. - If you have, let me know...

Estimated cost: Over $700 for the part, plus shipping and possible import fees... <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

Yep, that's where I'm at right now. Oh, I went back through the "Jen's Sporty" thread. After reading several times before buying the Miata-spec'd diffs and several times after confirming the 7.5" ring gear isn't compatible, I still get the impression that she installed 2 second-gen big-axle non-turbo RX-7 diffs in her Sporty. But she also commented that she did the welding, which I now wonder if it alludes to Lincoln-locking an open carrier (rear). I don't know. And she never responded to my PM through this forum. The other possibility is that she installed a Mazda LSD in the rear using a front pumpkin bolted to the rear axle housing. From other posts related to this topic, it sounds like the rear pumpkin will bolt onto the front axle housing. But that would mean she's running a 7" ring gear in the rear. What's the drawback with that? Anyone??? I'll add "test-fitting the front pumpkin on the rear axle housing" to my list of things to check out... <img src="/forums/images/graemlins/baby.gif" alt="" />

Plan "A" is a no-go. The Ford splines are too big, as I suspected, but refused to believe until I could test the compatibility myself. Still working on the other options... <img src="/forums/images/graemlins/patriot.gif" alt="" />

Well, the local 4x4 shop can't find an Eaton LSD. So getting one through them won't happen. On another note, I have a CAD program and made a drawing of a "hybrid" OBX case (ring gear side only) with the Kia-specs for the ring gear mount. Here's a comparison of the stock OBX case for the Miata and my red-headed-step-design. Sadly, I've been calling around to local machine shops all morning to get a quote, but can't find a shop that will even look at the job because:

A) "We don't do small-volume"

or

B) "We won't make automotive parts"

<img src="/forums/images/graemlins/angry.gif" alt="" />


So, if anyone knows of a machinist that can/will do the job for a fair price, let me know. And now for the pics (3D renderings)...


OBX stock casing...




The "hybrid" case with Kia's 7.5" ring gear mount...




<img src="/forums/images/graemlins/patriot.gif" alt="" />

Because I was unable to find a local machinist to bid on my job, I took my design to some on-line prototyping/machining companies. One is based in the U.S. The other is in Hong Kong with manufacturing done in China. The U.S. company responded with a bid exceeding $1200.00!!! <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'm still waiting to get a bid from the Chinese-based firm (which I suspect will be much lower). On a side-note, I have to say that, given the state of the U.S. economy, I would expect more companies would be willing to bid, and that the bids would be reasonable. Now I understand why our job-market and manufacturing-base is shrinking... <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

On related note, I decided to contact OBX Racing to see if they would be interested in machining a prototype. If it works, they will instantly have a new product line to fit the pre-'98 Sportage rear diff. And if they simply swap the axle gears with 28-spline x 29 mm (which is the same size as the splines on Honda's S2000, which they already sell LSDs for), then they will have products that cover all Sportages manufactured through 2005. Ah, but with my luck, they won't want to do it... <img src="/forums/images/graemlins/shiner.gif" alt="" />

<img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />

I have finally started work on the front diff. I have put the rear diff on the back-burner until I can find the "least expensive option" that is suitable for regular off-road use. As noted, that may involve having a the ring gear-side of the OBX case fabricated with the 7.5" ring gear mount. Or I will go with a Track Finder locker, if I can get one. Either way, the rear diff won't be done anytime soon.

As for the front, I have the diff assembly ready to pull. That is a lot more involved than it sounds - You have to pull the wheels, brake pads and rotors, unbolt the bottom joint on the knuckles (popping out the outer tie rods helps too), swing the knuckle to slide out the CV half-shaft, then pull the shafts out of the axle housing. However, the knuckle (a.k.a "spindle") seals were shot on both wheels, leaving the needle bearings (spindle bearings) corroding in petrified, water-contaminated grease and rust. The passenger side was the worse-off of the two. I didn't even realize it was a bearing until I noticed the black "rocks" I was pulling out of the muck used to be needle bearings. <img src="/forums/images/graemlins/zombie.gif" alt="" /> And that lead to a panicked-frenzy to find bearings and seals. They arrived today, along with 2 new outer tie rod ends (rubber boots were torn into 2 pieces). I have some photos of the project and will post them soon.

Anyhoo, I was holding off on installing the OBX diff until I was sure I could install the new side bearings. That worked out like a champ using my "poor man's bearing press"... a 3/8" bolt long enough to reach through the OBX case halves (separated into 2 separate pieces) and some steel washers & a plate. I simply lubed the bearing mounts with some grease and wrenched the bearings down (keeping a watchful eye to make sure they went on straight) - it worked great! I'll post some photos of that bit too when I have a chance.

So as it stands, I have the bearings on the OBX diff, the diff housing ready to drop, new parts to install (after I clean out the rust & crud a little better), and the OBX diff to reassemble and swap out with the stock carrier. I hope to get that all done tomorrow. I'll post the results after... <img src="/forums/images/graemlins/shiner.gif" alt="" />

<img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />

The OBX diff fits in the front-end & I have the diff housing back in the Sporty with the half-shafts installed. But that's as far as I've gotten. I had a battle with the backlash and preload when assembling the diff. And I think much of that was caused by the magnetic base on my dial indicator being just a wee-bit unsteady. In hindsight, I should have used a long bolt with short threads as a base for the indicator, and just bolted it through one of the pumpkin's mounting holes. I also found that my "bearing press" didn't seat the bearings completely. But I also found that using a section of 1.5" PVC or ABS pipe worked perfectly for finishing that job - just tapped them down with the pipe and a rubber mallet. <img src="/forums/images/graemlins/kewl.gif" alt="" /> If I would have used a thin ring of 1.5" pipe with the "press", the bearings would have seated perfect on the first go... I still have to get the knuckles and hubs together, oil in the diff, and finish up the front brakes. But I think that should all go smoother, now that I've found all of the bum parts and have the replacements in hand... right?!? <img src="/forums/images/graemlins/scared.gif" alt="" /> Pics will come soon...


<img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />

Update: I was able to get everything back together, despite a nasty bout with the flu (still recovering), to include replacing the front brakes and lengthening the front brake lines (plenty of line when the wheels hang). I road tested the front diff with the hubs locked in 2wd - no strange sounds or pulling. Then I did some short laps around the neighborhood in 4wd and everything felt fine. I'm now in So Cal and hope to do some testing on the dirt. <img src="/forums/images/graemlins/kewl.gif" alt="" /> I will let you know how it goes...

As it stands, the OBX diff works in the sporty's front end. And for the price and a little elbow grease, it may be a good option for getting a torsen-type LSD for the front axle. Again, I will let you know how it performs...

<img src="/forums/images/graemlins/patriot.gif" alt="" />

I'm back from So Cal. Unfortunately, my battle with the flu was far from over. It was merely shifting gears. And that kept me from getting out and testing the OBX diff in the front axle. However, the vehicle is handling better now and the new brakes are great!

Here are some photos of my "poor man's bearing press"...













Now for the spindle/knuckle bearings - here are a few pics of what I found on the passenger-side knuckle...


My CV half-shaft covered in greasy rust (mostly rust). But the splines were fine...




The backside of the knuckle with the seal still in place...




And a close-up of the crud and bearing... <img src="/forums/images/graemlins/zombie.gif" alt="" />




It took me a few minutes to realize these bits were the needle bearings...




Hey, isn't this thread about the OBX diff?!? Yep. And here are a few pics of the assembled diff... <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />







<img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />