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2012 JKUR Auto what's needed to regear

5K views 18 replies 5 participants last post by  Rb1boxer_3 
#1 ·
I have a 2012 JK Unlimited Rubicon Auto with 3.73 gears.

What do I need to prevent my vehicle from going into limp mode with 4.88 gears?
 
#2 ·
Nothing. Changing the gears will not make your jeep go into limp mode. You do not want 4.88s with an auto tranny though you should be looking at 5.13s or even 5.38s since you have a D44 front and rear.
 
#3 ·
Having a Dana 44 diff has nothing to do with the gear ratio you want. Not sure what ESP is saying here???

4.88s are absolutely appropriate for a 2012 with an auto and 35s (Not so much for a '07-'11). I'd even argue that 4.56s are a good choice if you do more street driving and want better fuel economy.

All you need is the stuff for the gear swap and an AEV ProCal to calibrate your computer.

--Sean
 
#5 ·
Yeah, 4.56s are hard to find, but they are out there. Superior and US Gear now have them, I believe. Because the WA580 tranny has such a wide ratio spread, you can get away with 4.10s and 35s depending on use. IF you live in flat areas, drive mostly highway, and don't load your Jeep down with weight (bumpers, armor, etc.), 4.10s and 35s would be adequate. I know it sounds crazy, but the 3.6/Auto/4.10s is still geared lower overall than the 3.8/Auto/4.88s.

For your use, it sounds like you might even be a candidate for 4.88s, but if you are happy with 3.73s stock, I think you'll be happy with 4.56s. If you decide on 4.88s, it won't be too low of a gear for your setup and usage. Remember the 3.6/WA580 combo can generally be geared one step taller than the 3.8/42RLE combo.

The issue with limp mode is that '12s have an additional module that needs to be changed when you calibrate the gear ratio. The older programmers only calibrated one, so when the '12s came out and you tried to program a new ratio, only one module was changed, creating conflict between the two modules. This is why limp mode happened (the vehicle thinks there are two different ratios installed). AEV has addressed the issue in the current tune and the ProCal is 100-percent compatible with the '12.

The JK braking system has enough braking that you shouldn't have an issue with stopping in low range with 35s and 4.88s, even on the 4:1 case. However, Teraflex has a great Big Brake Kit if you feel the need to get some braking back.

--Sean
 
#7 ·
Yeah, 4.56s are hard to find, but they are out there. Superior and US Gear now have them, I believe. Because the WA580 tranny has such a wide ratio spread, you can get away with 4.10s and 35s depending on use. IF you live in flat areas, drive mostly highway, and don't load your Jeep down with weight (bumpers, armor, etc.), 4.10s and 35s would be adequate. I know it sounds crazy, but the 3.6/Auto/4.10s is still geared lower overall than the 3.8/Auto/4.88s.

For your use, it sounds like you might even be a candidate for 4.88s, but if you are happy with 3.73s stock, I think you'll be happy with 4.56s. If you decide on 4.88s, it won't be too low of a gear for your setup and usage. Remember the 3.6/WA580 combo can generally be geared one step taller than the 3.8/42RLE combo.

The issue with limp mode is that '12s have an additional module that needs to be changed when you calibrate the gear ratio. The older programmers only calibrated one, so when the '12s came out and you tried to program a new ratio, only one module was changed, creating conflict between the two modules. This is why limp mode happened (the vehicle thinks there are two different ratios installed). AEV has addressed the issue in the current tune and the ProCal is 100-percent compatible with the '12.

The JK braking system has enough braking that you shouldn't have an issue with stopping in low range with 35s and 4.88s, even on the 4:1 case. However, Teraflex has a great Big Brake Kit if you feel the need to get some braking back.

--Sean
Sean is yours an auto?

Yeah, I am not sure if 4.56 or 4.88. Knowing that I rock crawl and highway drive daily at 80mph and tow, I want to find the sweet spot.
 
#6 · (Edited)
Your front axle or deferential does determine how far you can go with gears. Since the OP is running a D44 for both he is not limited to 5.13 with his front like a sport or sahara with the D30.

Here is a gear ratio chart you can pick from and a link to another thread you should read. http://www.wranglerforum.com/f33/gear-ratio-question-130244.html

 
#9 ·
Your front axle does determine how far you can go with gears. Since the OP is running a D44 for both he is not limited to 5.13 with his front like a sport or sahara with the D30.

4.88s are the a correct ratio for a manual but not for an auto. You should not be looking at those gears for your transmission. Search the board here and you will find out why.
Your comment is irrelevant because he is not close to needing the lowest gear ratios available for either diff. 5.13s are too deep for a 2012 running 35s. I have real-world experience with various '12 JKs with different axle ratio setups. The chart is a great resource, but not an end-all, be-all. You have other variables to factor in.

As fast as the OP says he drives, 5.13s will be spinning too high on the highway and fuel economy will suffer.

--Sean
 
#12 ·
Good point, I incorrectly assumed he said 35s. I re-read his post and see he never mentioned tire size. That is indeed my mistake. Probably came from the conversation about 35s I was having at the same time.

But you didn't correct me on anything. What differential you have only affects available gearing, not what gearing you should run. That was my point. Aren't internet forums fun?

Smyln, what tire size are you wanting to run? Obviously it is a crucial part of the conversation that is missing.

--Sean
 
#13 · (Edited)
Good point, I incorrectly assumed he said 35s. I re-read his post and see he never mentioned tire size. That is indeed my mistake.

But you didn't correct me on anything. What differential you have only affects available gearing, not what gearing you should run. That was my point. Aren't internet forums fun?

Smyln, what tire size are you wanting to run? Obviously it is a crucial part of the conversation that is missing.

--Sean
:flowers:
 
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