I've started my upgrade to 5.38 R&Ps, along with fixing some problems I had with my OBX helical LSD front diff (spec'd for the Miata) and upgrading the rear axle to 28-spline with a Track Finder locker. The mods to the OBX diff are in another thread. So I won't get into those details here. I have just finished the upgrade and reinstall of the front axle. The rear axle is still pending (hope to get it done this weekend). So here are the details on the front axle build...


Here's a pic of the new ring gear on my OBX diff...

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Before installing the new ring gear, I used a diamond-coated hone made for sharpening blades/knives to smooth out the high spots created from the drilling and tapping of the bolt holes. This pic was taken after the first pass with the hone. You can see the high spots as more silver-colored from the coating being removed.

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And here's the finished product. The process was a bit tedious because the diamond hone was the only tool I had that would cut into the hardened steel of the ring gear. But it worked out well...

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I had solid pinion spacers made by a company here in Nor Cal: http://www.weirperformance.com/solidpinionspacerkits.html. Spence Weir makes solid spacers for the Miata. I thought they would be a drop-in fit with the Sporty. But the pinion bearings, though nearly identical, are just different enough that the Miata spacer is a little shorter. So Spence fabbed up a pair that would fit the Sporty. The stock crush sleeve is on the left and the new spacer with adjusting shims are on the right... <img src="/forums/images/graemlins/kewl.gif" alt="" />


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The run out on the ring gear was only 0.001" after doing some work to "tune" the OBX diff. Again, those details are in the OBX thread...

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I was able to reuse the same pinion shim that was paired with the factory 4.77 R&P. The contact patterns appeared to show the pinion being too low. But when I tried shimming it up, the position of the contact patterns didn't move, they only became more narrow, which meant the amount of surface area contacting between the teeth was getting smaller. So I went back to the factory shim and proceeded to do the final install.

Here's the drive side...

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And the coast side...

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I did a complete tear-down on the front axle housing, cleaned it up "reel perty" and built 'er back up nice-n-tight! <img src="/forums/images/graemlins/notooth.gif" alt="" /> I was able to reuse the axle bearing, as it felt as good as new. But I did replace all 3 seals, for good measure. FYI - many parts catalogs show an inner and outer front axle bearing. There is only 1 bearing and it is a sealed unit. The parts catalogs show an RW101 wheel race and a #206 bearing. The dimensions on both are identical, implying they are both complete bearing units. So if you ever have replace this bearing, make sure you are getting the right part... <img src="/forums/images/graemlins/patriot.gif" alt="" />

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And here's a pic of the front axle, just before I popped it back in the Sporty!!!

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And now for some quick notes...

I had first ordered the Timken pinion bearings (32206M and 32207M) because they were close-out priced. The bearings are the same as the 32206 and 32207. But the height of the bearing races differ only by about 0.002". I found the Timken bearings to be rough compared the National bearings (32206 & 32207) I had picked up later, after I decided to rebuild both the front and rear diffs. They were so rough, I was concerned that they would wear out prematurely. And for all the work it takes to rebuild the front diff, I didn't want to take the chance. I recommend using the National bearings. They are very good quality and will spare you a lot of hassle.

Another important bit of trivia is that the 32206 and 32207-series bearings have a different cone angle than the factory bearings (32206C and 32207C). The aftermarket bearings are much stronger and handle a higher load than the bearings Kia uses. I say the 32206 and 32207 bearings are the way to go for a stronger diff...

The solid spacer: I really like it. Yes, solid spacers take a bit more work to set up. But they are worth the $$$ and effort, in my opinion (oh-pinion... <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" />). The easiest way to set it up is to have a set of "setup" bearings, which have the bore sanded out just enough that the bearings will slide on and off the pinion - no press required. That will let you set up the preload using the newly-installed races without having to remove the inner pinion bearing (32207). I ended up damaging the roller cage on the 32207M bearing during this process. So the Timken bearings are now my setup-set. If you are doing both the front and rear, it's worth dropping the extra dime to make a pair of setup bearings. Also, here's the most cost-effective tool to purchase for measuring the bearing preload: http://www.parktool.com/product/torque-wrench-tw-1. They cost about $40. But this is one of the few deflection-beam-type torque wrenches that measures in the low inch-pound range. And you can use it for measuring your wheel bearing preload when you pull your front hubs too!!! <img src="/forums/images/graemlins/kewl.gif" alt="" />


That's all for now. I hope to post the details of the rear axle build very 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="" />