Upgrade Check

I am finalizing my tire refresh on my 08 JKU Auto. I am looking to run 37" BFG KM2s. I am replacing my front D30 with a Currie RockJock 44 and ARB. I have an X with a factory rear locker (which should have 32 spline axles) that will be regeared to 5.38s to match the new front axle. I have a 3" lift that has already been tested to clear 37s (with rock rail and pinch seam trimming)

I also have a 1310 front DS and cannot wait to feel power back in my jeep. Members here are an inspiration and I've been very patient with my jeep, but its now time to grow.

Have I overlooked anything? This is my jeep without any trimming on 37 maxixis, so I believe it will work out for me.

I'd personally do 5:13 over 5:38.
It's the same thing as 5:13 in a Dana 30.
Teeth are just too small.

This. 5.13 is a safer bet and should run really well with the 37s. I'm running them now in 35s... A little low on the highway, but performance is awesome on the rocks.

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Build Thread - Adventures of Fiona - https://wayalife.com/showthread.php?t=47407

I have 5.13s on 37s with the 3.8. It is tolerable and much better than the stock 4.10s. 5.38s would be better but the pinion gear is tiny with that set up on 44s and will be a weak point.

I appreciate the feedback on the gears. I've been looking for posts where 5.38s are breaking more than 5.13s and I haven't found much of anything.

Is this speculation or am i just not finding these discussions?

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It’s not speculation that the 5.38 pinion gear is tiny, and that means more stress on the gears.

If you’re not going to offroad it, tow, or put in a supercharger, turbo, or V8, you probably could get by with the 5.38.

I have not seen a broken 5.38 in a 44, but I have seen broken 5.13s in a 30, which is a similar issue. Tiny pinion gear can’t handle big tires, even with the underpowered 3.8 engine.

I've been running the 5.38's in my '07 6 speed on 35's, for a few years now. While it is geared too low for everyday highway driving, I do love how it performs offroad. It spends about 75% of it's time offroad, as it's not my everyday driver. I think it all comes down to your offroad driving habits. I get out of the throttle any time it starts to buck, and I don't do deep mud. The only issue I've had was with my rear Auburn Ected locker last October. The case bolts backed out and dropped debris into my ring gear, destroying the gears. I was only a couple of days over my 3 year, 15k mile Extreme warranty on that, so 4WP honored it and fixed it. I would advise you to think ahead. I never planned on running 1 tons when I first got my Jeep. I upgraded to Rubi 44's, and looking back now...should have just waited and applied that money to a set of bolt in 60's. Think about what you want for your Jeep in the long run, and plan for that.