Finally... I have an update!!! I was able to pull my front axle and tear down the OBX diff. I found the cause of my trouble - the reason why the diff was catching and banging when I tried to turn left with the 4x4 engaged. The sloppy machining tolerances allowed one set of the helical gears (planetary) to contact the opposing axle gear ("sun" gear) when the vehicle was turning to the left. Straight was fine, as no gears move within the casing. And the right turn was fine because the gears didn't touch (barely...). Here's a pic of the gears that were catching, chipped teeth and all. <img src="/forums/images/graemlins/zombie.gif" alt="" />







It took a bit of thought, but I was able to come up with a fix: I took the gears to the bench grinder and beveled them so they can overlap without catching teeth. I tested the mod thoroughly to ensure the problem was solved. I did this by assembling the casing with all parts except the belleville washers, inserting a spline shaft in one of the sun gears and spinning the gears while holding the shaft upright with the diff on top (like a head on a pike... <img src="/forums/images/graemlins/evil.gif" alt="" />). The weight of the diff will push the sun gear up while the weight of the opposing planetary gears will pull them down. The lack of the spring washers allowed the "system" to act as if it were under sufficient load to overcome the preload of the washers, which is exactly what happens when the wheels turn at different speeds. If both gear-sets turn freely without hangups (have to test both sides this way), then the problem is gone. <img src="/forums/images/graemlins/kewl.gif" alt="" /> Here's some pics of the modded gears...








And here's a pic of how the gears load into the case - the heavily-beveled ends all face toward the center, because that's where the overlap occurs...




Once I had it all sorted out, I reassembled the case and proceeded to install my new 5.38 R&P set (those details in another thread). Here's a tip for anyone that may decide to give the OBX diff a try - It's easier to torque the case bolts if you mount the diff in a vise like this (I torqued mine to 40 ft-lbs using red thread locker)...





Another issue I ran into while setting up the R&P was that the ring gear mount was out of "true" by about 0.004". That doesn't sound like much. But when the ring gear wobbles towards and away from the pinion, it can and will throw your backlash off. I found the simple way to fix it was to file the centerline-face of the diff case (ring gear side) to eliminate the high spot (the area that measures farther away from center). It took a few hours of filing (I used a diamond hone for sharpening blades), assembling the casing (no gears... no need) and loading the diff into the housing for measuring. But it worked! <img src="/forums/images/graemlins/cheers.gif" alt="" />




Once that was sorted out, I did the final assembly on the diff and finished up the 5.38 R&P upgrade of my front axle (those details in another thread)...




I still have to put my fix-it-mods to the test. But I can't do that until I finish installing the 5.38 R&P set in my rear axle. I hope to get that done next weekend, time permitting. I am pretty sure the problem has been solved and the diff will function normally. That said, I want to table a few "insights". First, the direction of the sun gears may not make a difference after all. I say this because, after sorting out the issue with overlapping gears, I came to realize the following...

1) No gears turn when the wheels turn at the same speed (this isn't new and has been noted earlier in this thread).

2) Because the gears are not moving under the conditions of point (1), the pulling inward or pushing outward of the planetary gears against the case is a non-issue. It doesn't matter. (That's an epiphany)

3) When turning, one set of planetary gears will pull towards the center while the corresponding/meshed sun gear will move away from center. The opposing gear set will perform oppositely: the planetary gears will move away from center while the corresponding sun gear will move towards center. When you turn left, one set of gears shift to center. When you turn right, the other set of gears shift to center. This is a big epiphany!!! (For me, at least).

Thus, the direction of the sun gears, as mentioned earlier in this thread based on references from other OBX discussions on other forums, doesn't matter. This is due to the fact that the shifting of gears towards and away from center is dependent on variation in wheel speed (i.e. one wheel rolling faster than the other). And each gear set will move towards or away from center only when the wheel speed varies specifically (like turning right or left). The critical point of this is that the gear sets on one side turn in the opposite direction of the other side when wheel speed differs. And if the planetary gears from one side overlap the sun gear on the other side, the teeth of both will catch - catastrophically. This will happen because the planetary gears from one side and the sun gear from the other side BOTH MOVE TOWARDS THE CENTER under one specific turn condition (left or right). That's why bad things happen if the machining tolerances are crap... And that's what happened to me. Fortunately, the fix was relatively simple.

Taking all things into account, I am hesitant to recommend the OBX diff - assuming it works well off road. I say this because the quality of the product is low. It's a made-on-the-cheap-in-China product. The machining tolerances are sloppy and I had issues with the quality of the casting (case had pits, pockets and cracks). I was able to fix the issues (cracked case had to be exchanged - not an easy process). And the fixes, as I've noted, weren't too difficult, just tedious. For $279, a little elbow grease will give you a tough little diff. But the OBX diff is now selling for $358-$378 on eBay. That's another $100 over what I paid. And for that price, I'd shop for a quality-made diff that will drop in without hassle, even if it was a clutch-type LSD (or a Track Finder locker for the front). I will report back when I have had a chance to test the mods on the OBX diff, and assuming they work, how the OBX performs on the trail. Wish me luck...


<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="" />