I'm even considering eating the cost to upgrade my 4.88's to 5.13's with my 35's for that small 5% 300 RPM diffrence! Even on a budget, it drives me crazy that my auto won't hold overdrive on flat ground, and 5.13-5.38's are in my future also.

I'd really like to hear additional feedback on the reliability of 5.38's

 

This was the breakdown provided to me by my trusted lift shop buddy who was a former rep for Dynatrac and had plenty of experience with axles and ring gear size. The cost to me for 5.13s and 5.38s was the same so he had no hidden agenda on selling me one way or another other than based on experience and performance. Now that I think of it, the 5.38s did cost a bit more and he told me the increase in $ wasn't worth any increase in potential performance gain.

Just my 2 cents since I already have 5.13s with a relatively large tire and am happy. I'm sure 99% of us on here wouldn't know/see the difference in ring gear size but would appreciate the extra $ in our pocket.

 

My ideal spot to be in, as I have a 6 speed as well, is being between 2000-2200rpm at 70mph in 6th gear. I'm in a currently very light 2 door, w/35s and that's what it takes to efficiently maintain speed and gas mileage. Add in some extra weight, bumpers, an unlimited and whatever else then I would bump the rpm up a bit. I've got plenty of gear in the transmission on the low end, for regular on road driving and have actually thought harder about a transfer case than gears.

I messed around with the Superchips idle control settings (800-1500) and thought it was very cool and useful. Being able to just ease off the clutch with a foot on the brake with a juiced idle and not using the handbrake was great. No feathering of the throttle and it just went when easing out the clutch. The unfortunate part is that the feature only works with the Flashpaq plugged in, but if available full time I would just juice it to around 1200 and leave it there. Definitely cool.

As for which gears I really think a ton of it comes down to personal preference and peoples expectations. The automatic guys have it a lot tougher as I could be just as happy with a 5 speed and I have plenty of gear in first.

 

My quest here is just for knowledge as well and I really don't know what the differences are in durability, just the pinion gear didn't make sense. More teeth on the steeper ring gear could be at issue and perhaps the price as well.

As for me, my experience with gears have been for a totally different purpose where the rule of thumb was under gear and over convert. Here of course the intent and purpose of the vehicles are totally different.

Anyway, perhaps my tone came off differently than I intended and I apologize.

 

I am also very intrested to know if anyone can speak to the reliability of 5.38's? 5.13's seem to be pretty tested but with an auto and eventually 37's I would hate to say i wish I would have gone with the 5.38's. My main concern is reliability as well as impact on other equiptment (so basically longevity). For now the JK is my DD but a company car should be in the near future. Once that happens the jeep will be my toy . With that being said mpg isn't on the table for me. Anything above 8 is better than my last Jeep.

 

I've got 5.13s and 37s, wish I had 5.38s. I can't use overdrive most of the time.

 

I got a phone call today that lead me to believe I might have lunched my rear axle enough to make it cost more effective to throw a 60 under it. A visit to the shop over lunch changed things. It looks like I've got a bad pinion bearing. The alarmed me over the phone by saying both my axle tubes rolled and were bent. Upon closer examination it looks like the plug welds on the tubes gave way and the tubes rolled 1/16" but the tubes are straight.

All that is a long way to say that I when I though I'd have to buy new gears and locker for a D60 that I would DEFINETLY go with 5.38's. I'd have pulled the 5.13's out of the front and had 5.38's installed in the D44. I've got 35's and 5.13's right now and I spin 2600 at 7500. I would not want to go to any lower rpm; I'd actyally prefer to be at 2700-2750. Were I doing it again today, even if I was going to run 35's I'd go with 5.38's. And that is doubly so since I'm going to go to 37's as soon as I can.

Everybody said that 4.88 were the way to go and that 5.13's were weak. I've taken out two CM axle shafts without damaging the R&P and somebody else just posted that he took out a front shaft and his 5.13's were good. I'd take a chance on the 5.38's being ok. FWIW the above is automatic specific.

 

Your the second guy I've heard that spin the tubes in the rear axle. Nice work

 

I don't baby this puppy at all!

We're going to reweld the plug welds. You can sure see that the weld gave way and cracked. If I had more time I think I might roll them so more, somewhere between 7 or 8 degrees, I'll bet my spring perches would be horizontal. I wonder if I dropped the axle and brought it into the local driveline shop he has the equipment to do it?

 

5.38's, MTR40's, and the Superchip 93 octane, PSC Hydraulic assist......


I love the way it drives!