2012 stock JKU Sahara Regeared From 3:21 to 4:1 - advise? - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 6 Old 08-12-2015, 07:16 PM Thread Starter
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2012 stock JKU Sahara Regeared From 3:21 to 4:1 - advise?

I purchased a used 2012 JKU Sahara, automatic with factory tow package, The dealership advertised it as having the factory max tow package (comes with 3.73 gears). Turns out my JKU only had 3.21. Per Jeep in order to reach the max tow of 3500 lbs I would need to swap the 3.21s out. The dealership agreed to pay for regearing at a reputable local shop. At the suggestion of the shop I had 4.1s installed on my stock JKU Sahara. After installation it threw out an error code - the shop said I could have the computer flashed to accept the new gears or install a tuner (opted for tuner).

The jeep drives fine for the most part - rpms are much higher (avg just over 2000 "cruising", sometimes hitting 3000 before shifting to the next gear - 4000 when towing). There seems to be excessive heat coming from under the jeep after driving around (not just when towing)- but we've also been experiencing outside temps in the mid 90's so that could be the issue with that.

I've been looking for guidance online but the more I learn, the less I know ;-p My questions are these: Can a stock 2012 JKU Sahara handle 4.1s without further modification (tfr case, axles, etc.)? Now that I have 4.1s what are the first changes should I look into making (tire size etc.)? Should I be concerned about the high rpm's or "it is what it is"?

Relevant stock specs for 2012 JKU Sahara:
5-Speed Auto W5A580 Transmission
Command-Trac Shift-on-the-Fly 4WD
Next Gen. Dana 30 Solid Front Axle
3.21 Rear Axle Ratio
Next Gen. Dana 44 HD Rear Axle
Conventional Differential Frt Axle
Conventional Differential Rear Axle
3.6L V6 24V VVT Engine
P255/70R18 OWL On/Off Road Tires
18X7.5 Whl
Transferase is 2.72-to-1 reduction I believe

Thanks in advance :-)
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post #2 of 6 Old 08-12-2015, 07:26 PM
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Go to any vendor that sells the AEV ProCal, buy it, and recalibrate for the new gear set. The SuperChips Flashcal will do the same thing. Your stock 30/44 axles will handle 4.10's just fine. The only drawback to the 30 is being a little weak when you get above 37" tires. At that rate, 4.10's would be on the bottom edge of being acceptable anyways, so no worries there. You'll need a FlashCal or ProCal anyways if you want to run bigger tires down the road, so it's a worthwhile investment.

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post #3 of 6 Old 08-12-2015, 07:46 PM
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How many miles since install? The first 500 miles not Supossed to tow and not go more than 30 or so miles before stoping and letting them cool off. then after 500 miles change the diff fluid. They get really hot while breaking in
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post #4 of 6 Old 08-12-2015, 08:03 PM Thread Starter
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Originally Posted by bcrane View Post
How many miles since install? The first 500 miles not Supossed to tow and not go more than 30 or so miles before stoping and letting them cool off. then after 500 miles change the diff fluid. They get really hot while breaking in
D'oh! I was not aware of the break-in period - makes sense though. It's only been a couple of hundred miles since install. Unfortunately I've already towed the family camper (just over 2k lbs loaded, 40 miles each way) and I routinely drive 40+ miles one way. I wonder what sort of damage I may have done...any suggestions as to what to look for?
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post #5 of 6 Old 08-12-2015, 08:30 PM
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Not sure, if you're over the 500 miles i would just change the fluid. Some people swear by the break in. I just followed what my installer suggested, they were putting off alot of heat while under the break in period. You in might google gear break in, the info that's out there very a little.
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post #6 of 6 Old 08-12-2015, 08:33 PM
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I brought it back and he pulled the covers and inspected the wear patern to make sure it was still a good pattern. After the 500 miles.
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