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Re-Gearing a JLU

Swanny297

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The Rubicon 220mm ring gear and the LSD 44 on the sports etc are the same 220mm ring gear. The only difference is the tube length is wider on the Rubicon and the locker of course. Both are 32 spline now as well.

Northridge’s website does not allow you to select 220mm if you have a sport so you’ll have to change your vehicle. They told me awhile back they were going to fix it.

I’m going 4.88’s with my 35’s. I have a manual and want to get my crawl ratio as low as possible. 4.88’s will take me from 48:1 to 68:1. I miss my Rubicon t-case!
I am new to gears so this may be a dumb question - I have a Sport S with LSD - if the gears are the same as the Rubicon in the rear does that change the 3.45 gear ratio?
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intentsrig

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I am new to gears so this may be a dumb question - I have a Sport S with LSD - if the gears are the same as the Rubicon in the rear does that change the 3.45 gear ratio?
Nope. We still hve 3.45 but in a 220mm rear ring gear size.
 

Ponyracer

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Remember, when talking gearing, you’ve also got to take into account for the heavy tires and extra weight we put on our vehicles with winches, sliders, and bumpers. Personally I’m going to 4.88’s. A few extra rpms on the highway isn’t going to hurt. It’ll be nice to have my top 2 gears back!!
 

GARRIGA

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If I understand my friend who has been in the drive line business for years correctly, to establish a gear ratio close to factory specs a rather simple formula is applied. Determine the size of tires you want to run, multiply that tire diameter by the gear ratio currently in your vehicle then divide that total by the diameter of the tire the factory provided.

Perhaps an example will provide clarity. I purchased a 2018 JLU Rubicon it came with 33" tires and has a 4.10 gear ratio. Suppose I would like to run 37" tires. The calculation to get back to factory specifications is 37 (the tire size I want to run) multiplied by 4.10 (the gear ratio currently in the vehicle) = 151.7 divided by 33 (the diameter of tires the factory provided) = 4.5969697 Now compare the results of our formula to the available gear sets and choose the gear set that most closely matches, in our case it would be 4.56

I hope this is helpful and sheds a little light on the subject. Disclaimer: I am not an expert, nor do I play one on TV. Seek advise from real experts before selecting your gear set.... or use the calculation above at your own risk.

Happy Jeeping.

Cheers!
I've seen that on YouTube. Seems simple enough. Guess I'll be going 4.56, as well. Do need 8th gear as mostly run 80 on highway for daily commute and weekends to go fishing.

I think many are considering 4.88 with 37s because that was the sweet spot for the JK but the new auto transmission does change things. Would explain why Jeep can go to 33s from factory. Still thinking those with mostly off-road aspirations will seek 4.88s as that will give them much improved performance with the new 8 speed but not sure how it would change the dynamics with the manual. Probably remain the same as with the JK? Wasn't the JK also 6 speeds and I think the gearing is similar.
 

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Question does any of this VOID YOUR WARRANTY?????
 

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deitrick1

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Just got my JLUR back from shop. Now have 4.88 gears, but still waiting for back ordered wheels, so still have 33s on.

Noticed the ESS warning light on the dash. After getting home from the shop, I reflashed using my Superchips Flashcal and all went well, but ESS warning light is still on. Even after a 10 min drive. I've heard tails of the light staying on for a day or so before it clears.

Anyone else have this issue?
 

utefan

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Just got my JLUR back from shop. Now have 4.88 gears, but still waiting for back ordered wheels, so still have 33s on.

Noticed the ESS warning light on the dash. After getting home from the shop, I reflashed using my Superchips Flashcal and all went well, but ESS warning light is still on. Even after a 10 min drive. I've heard tails of the light staying on for a day or so before it clears.

Anyone else have this issue?
Rudy please post an update once you get your new wheels and tires and how they work with the 4.88 gear ratio. Two areas of specific interest for me, 1) how "peppy" does it feel starting out, and 2) would you please post your RPM at 80 MPH on flat ground in your top gear?

It will be a bit of an apples and oranges comparison as I have the auto 8 speed, but I live in Utah near the canyons and every where I go I'm going up or down hills. So even though the formula says I should run 4:56, I may be better served going with lower gearing. Unfortunately I do a fair amount of highway driving so "reasonable" (LOL) MPG would be nice.

Many, many thanks in advance.

Happy Jeeping!

Cheers
 

Sharkbite22

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Just got my JLUR back from shop. Now have 4.88 gears, but still waiting for back ordered wheels, so still have 33s on.

Noticed the ESS warning light on the dash. After getting home from the shop, I reflashed using my Superchips Flashcal and all went well, but ESS warning light is still on. Even after a 10 min drive. I've heard tails of the light staying on for a day or so before it clears.

Anyone else have this issue?
I have the exact issue. Picked mine up Friday from having 4.88's installed and the ESS light and "service ESS system" message is on dash. It has come on every time I drive now except once when the stop/start actually worked at a light but then a few minutes later the light came back on. I have a Flashcal on the way. Maybe it will reset when I set the gear ratio and tire size. I turn the ESS off every time I drive anyway.

On a positive note, 2 door six speed on 35's is fantastic with 4.88's! first gear is extremely short now but it definitely has some "pep" back. I had to be on the interstate on a slight down hill to use 6th gear on the stock gears. Now I can cruise along in 6th on a back road at 45 mph. Only had it on the interstate briefly since the swap, but looked to be about 2200 or so rpm at 70 mph. It drives great and with the MBRP exhaust giving it just enough sound to shift by ear again, the fun to drive factor went up even more!
 

deitrick1

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I have the exact issue. Picked mine up Friday from having 4.88's installed and the ESS light and "service ESS system" message is on dash. It has come on every time I drive now except once when the stop/start actually worked at a light but then a few minutes later the light came back on. I have a Flashcal on the way. Maybe it will reset when I set the gear ratio and tire size. I turn the ESS off every time I drive anyway.

On a positive note, 2 door six speed on 35's is fantastic with 4.88's! first gear is extremely short now but it definitely has some "pep" back. I had to be on the interstate on a slight down hill to use 6th gear on the stock gears. Now I can cruise along in 6th on a back road at 45 mph. Only had it on the interstate briefly since the swap, but looked to be about 2200 or so rpm at 70 mph. It drives great and with the MBRP exhaust giving it just enough sound to shift by ear again, the fun to drive factor went up even more!
Your description of the issue is exactly what I am facing. The ESS will be okay for the first min or so (may even be speed related-throws error once I hit over xx mph), and then the error and it's disabled.

I already have the Superchips Flashcal and it did not help me a bit.
 

intentsrig

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I have the exact issue. Picked mine up Friday from having 4.88's installed and the ESS light and "service ESS system" message is on dash. It has come on every time I drive now except once when the stop/start actually worked at a light but then a few minutes later the light came back on. I have a Flashcal on the way. Maybe it will reset when I set the gear ratio and tire size. I turn the ESS off every time I drive anyway.

On a positive note, 2 door six speed on 35's is fantastic with 4.88's! first gear is extremely short now but it definitely has some "pep" back. I had to be on the interstate on a slight down hill to use 6th gear on the stock gears. Now I can cruise along in 6th on a back road at 45 mph. Only had it on the interstate briefly since the swap, but looked to be about 2200 or so rpm at 70 mph. It drives great and with the MBRP exhaust giving it just enough sound to shift by ear again, the fun to drive factor went up even more!
Ahh I want to regear so bad! Sounds awesome! I’m just waiting for someone to release a locker. Have you put it in 4lo yet?
 

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Sharkbite22

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Ahh I want to regear so bad! Sounds awesome! I’m just waiting for someone to release a locker. Have you put it in 4lo yet?
Still breaking them in but hopefully in week or so I will be ready to test it out. I had the same setup in my 07 JK and the crawl in 4 lo was so much better
 

deitrick1

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So upon further analysis, I have determined the ESS warning light goes on once I hit 4th gear and stays on until I shut the Jeep off.
 

WXman

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Question does any of this VOID YOUR WARRANTY?????
I can't tell if you're serious or kidding. :) But if you're serious...yes putting 4.88s in your Jeep will kill your warranty. They could make the case that the gearing is putting undo stress on everything including your transmission, t-case, driveshafts, diffs, axle shafts, basically the whole nine yards. They could even claim the high RPMs are to blame if you have any engine troubles, and there have been cases of valvetrain failures on Pentastar engines already for 2018 not related to axle gearing. But I wouldn't want to put myself in that position.
 

PavementWarrior

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I can't tell if you're serious or kidding. :) But if you're serious...yes putting 4.88s in your Jeep will kill your warranty. They could make the case that the gearing is putting undo stress on everything including your transmission, t-case, driveshafts, diffs, axle shafts, basically the whole nine yards. They could even claim the high RPMs are to blame if you have any engine troubles, and there have been cases of valvetrain failures on Pentastar engines already for 2018 not related to axle gearing. But I wouldn't want to put myself in that position.
Then the same is true with bigger tires, no if ands or buts.
 

WXman

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Then the same is true with bigger tires, no if ands or buts.
Except, I can throw my factory wheels and tires back on the Jeep in 15 minutes if I need to go in for service. Can't do that with a ring and pinion swap.
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