The ARB improves over the 4 pinion also. ARB > OEM 4pinion > OEM 2pinion and I think the gap between OEM 4 and 2 is a little closer than comes across on the forum. I believe as more newer ones get banged on you will continue to see 4 pinions fail closer to the rate of 2 pinions (which is still low in the big picture). Only time will tell, but for the sake of guys with the newer ones I hope I am incorrect.
^^^I think tabraha right about this. The last 3 we've seen on here have all been of the 4 pinion variety. The 2-pinion/4pinion refers to the spider gears.
Here comes some off the cuff knowledge that I've gained from really learning how differentials work...... The pinion gear is tapered and grooved so the teeth on it are spiraled. That means that as it spins in the teeth of the ring gear, it's actually trying to "pull" away from it. That's natural, and can be set up tighter to allow more room to pull away and still be engaged. The carrier, or center section (what the ring gear bolts to) on our trucks is the actual weak link here. As the pinion gear is trying to pull away from the ring gear under load, the carrier flexes. We're talking thousands of an inch.
Over time, parts start to wear. The sludge that you clear off your differential drain plug is coming from the wear of everything. What started out as 5/1000s now may be 9/1000s. When we put that system under load from climbing, spinning, bouncing and suddenly that wheel gets traction and grabs, the shock load is going through the entire system. The carrier flexes or deflects just a hair and causes the pinion gear to pull away too far from the ring gear. The teeth bind and shear off. As more of our trucks see the milage and wear and tear of use, this scenario will be more prevalent.
The carrier (what the ring gear bolts to) of a TJM or ARB locker is more ridged and will not flex, or won't flex nearly as much, allowing the pinion gear to try and pull away from the ring gear, but still stay within tolerances. That, coupled with gears that are set up correctly means something else will become the weak link when the entire system comes under load. That's a good thing. Replacing a U joint or cv is easier/cheaper than replacing gears.
If I'm wrong here, someone will correct me. I'm looking forward to getting this thing disassembled to get a good look at the center section. I'd like to see if I can tell that it flexed. Do they crack/split? There would be no way to ever know that that's what caused the failure unless we saw that, correct?
I never paid too much attention to all the threads about this. I always felt it wouldn't happen to me. I don't know where I fall in the scope of mild to wild use for the 100 Series crowd. I go out often, that's all I can say. I've done runs with jonharis and bluecruiser who are fully locked and I was not. Whether I broke because of something I did wrong or it was just my time, I'll never know. I wasn't on a dirt road, I was on a pretty difficult section of a moderate trail. Others have broken on lesser obstacles on mild trails. If you're reading this and you haven't broken yours yet, it's just a matter of time as your vehicle ages and parts wear. Spressomon is 100% correct when he says this should be your first mod. Or if its not, then just keep a jar of money on your dresser and every time you go out, put a few dollars in there for when this happens.
