JLUR on 37s regear 4.56 or 4.88

intentsrig

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I have 5.13’s 6 speed w/ 37’s which feels great.

However, I have recently picked up a set of 35’s and the 5.13’s feel even better! So much so that if I were to do it again I would go 5.38’s with 37’s. That’s how much more power I feel I have gained back with the 35’s.

5.38’s and 35’s would be a bit excessive though so really only for 37’s. I am keeping the 37’s as well so 5.13’s is good for both.





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Drawls

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I, too, am in Southern Oregon. Nothing is flat. I have a 6 speed and almost always use forth for everything on my 18 JLUR. I am thinking that 5:13 is the way to go because the 3.6 is high revving low torque engine. and I would like to use more than 4 on the floor.

Wish I could find someone who would do the switch locally -- I guess I need to go to Reno.
I have a buddy who has a shop here in Roseburg,Or kelter off-road if you want I can get you his contact info.
 

Drawls

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I have 5.13’s 6 speed w/ 37’s which feels great.

However, I have recently picked up a set of 35’s and the 5.13’s feel even better! So much so that if I were to do it again I would go 5.38’s with 37’s. That’s how much more power I feel I have gained back with the 35’s.

5.38’s and 35’s would be a bit excessive though so really only for 37’s. I am keeping the 37’s as well so 5.13’s is good for both.
Yea I would agree. the only thing that sucks about 5:38 in the 44’s is the pinion gear is so small.
 

bnidasio

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I have 5.13’s 6 speed w/ 37’s which feels great.

However, I have recently picked up a set of 35’s and the 5.13’s feel even better! So much so that if I were to do it again I would go 5.38’s with 37’s. That’s how much more power I feel I have gained back with the 35’s.

5.38’s and 35’s would be a bit excessive though so really only for 37’s. I am keeping the 37’s as well so 5.13’s is good for both.
I’m torn between 4.88 and 5.13’s. I’m a 2 door Rubi on 37’s. Could you post your RPM @ 60, 65, 70, 75MPH. Thanks!
 

Hotfoot22

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I have a buddy who has a shop here in Roseburg,Or kelter off-road if you want I can get you his contact info.
I would like his number. It is barren in the Medford area for this kind of thing. Thanks.
 

Drawls

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I would like his number. It is barren in the Medford area for this kind of thing. Thanks.
Lenny Coopride
1-541-580-7079
He usually has gear sets in stock. Tell him I gave you his number. josh Manson
 

FLECK-5

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This discussion of preferred gear ratios is very confusing because the various opinions don’t always clarify whether they have a 6 speed manual or an 8 speed automatic. The transmissions have a different number of gears and their final gear ratios are different with the manual 6th gear at 0.72:1 compared the 8th gear at 0.67:1. This discussion should be split up into a manual and an automatic discussion.

From my experience and the research I have done, below are my conclusions.

I have been driving with 37’s for almost a year with 4.10’s and I can’t stand it anymore for highway driving. 8th gear is rarely seen on the highway because the RPM’s are way too low. Using a spreadsheet calculator I found on this forum, quantifies my experience. To get into the start of the powerband for the 3.6L (2,000 RPM’s) I have to be driving over 77mph. Driving at 70mph puts me around 1,800 rpms which is worthless power wise.

Manuals need to be one size up from automatics, i.e a 4.88 in an automatic would be like a 5.13 in a manual.

In an automatic, 4.56 with 37’s is similar to stock 33’s with 4.10’s, but it does not compensate for the extra drag caused by the 37’s. Would be a great ratio for 35’s in a sport or Sahara. Probably not worth the cost for a Rubicon as it’s not much different then 4.10’s.

In an automatic, 4.88 with 37’s will feel like stock 33’s with 4.10’s as it compensates for the extra drag caused by the 37’s. For highway driving 8th gear will operate like an overdrive and the transmission will jump between 7th and 8th depending on incline, wind, and acceleration. Cruising on the highway at 75 mph should be around 2,250 RPM’s. When it downshifts to 7th at 75mph it will be around 2,800 RPM’s which is plenty of power for passing. This is the optimal ratio for returning a jeep back to feeling stock but with 37’s.

In an automatic, 5.13’s with 37’s will feel faster then stock 33’s with 4.10s and users who pick this option are looking to boost performance over stock. Cruising on the highway at 75 mph will keep you in the powerband of the motor at around 2,400 RPM’s, but there will be no more shifting to a higher gear to get better gas mileage or reduce engine noise.


I am dropping my Jeep off tomorrow to have the 4.88’s installed. Can’t wait to get it done and get the Jeep back to the correct gearing.
 

Gotcha-Again-LOL

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One thing you also have to think about is ring and pinion tooth strength...its really interesting how many guys i have watched wheel on 37s and 38s with the stock 4.10s with zero issues for over a year and then when some switch to 5.13 or 5.38s they blow a ring and pinion soon after...when you dive down that deep in ratios it reduces the tooth strength so if you wheel hard stick with 4.10-4.56 and you will save your R&P
 

wibornz

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So, I put 37s on my JLUR at 93 miles. Basically drove it home from the dealership. I drove it with stock 4.10 gears for a year and wheeled all over the US. Put on 19,000 miles and it is not a daily driver. I pulled a small camper out to Ouray, Colorado and Moab, Utah from Michigan. I was getting 17 to 19 mpg on the hwy with out the camper and about 13 to 14 mpg with the camper. I almost never saw 8 gear. One trip out west and I was ready to re-gear. My Jeep is heavy, add tools, steel bumpers, heavy spare tire carrier, winch, ATX Slab wheels and 37 Cooper STT pro tires. plus other random shit...gear that I take with me. Plus my big ass and my loving wife. So I re-geared to 5.13 gears. Yukon gear kit....

The gear swap pulled over a second off 0-60 times. I see 8th gear all the time even in the city. I lost about 1 mpg and the motor is right where I want it at 70 mph.

Pic is of 70 mph on cruise in 8th gear.

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I love it with 5.13 gears. I even see 8th gear pulling the camper.

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FLECK-5

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Picked up my Jeep tonight after getting the 4.88’s installed. Drove home on mostly highway driving. It’s like my Jeep came back to life. Jeep cruises in 8th gear again at 75 mph and downshifts to 7th as needed like it’s designed to do. Love it. Drives much better around town too. First gear is quick off the line. So glad I got it done.
 

Remmy

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One thing you also have to think about is ring and pinion tooth strength...its really interesting how many guys i have watched wheel on 37s and 38s with the stock 4.10s with zero issues for over a year and then when some switch to 5.13 or 5.38s they blow a ring and pinion soon after...when you dive down that deep in ratios it reduces the tooth strength so if you wheel hard stick with 4.10-4.56 and you will save your R&P
This ^^^

I really want to go 5.13s but I think I'll stick with 4.88s to split the difference.
 

wibornz

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This ^^^

I really want to go 5.13s but I think I'll stick with 4.88s to split the difference.
Is there a rash of 5.13 pinions failing on the new JLs...... I might be concerned if it was a modded diesel truck, but hey, my gears came with a lifetime warranty including labor from the shop that did my re-gear. So I am not worried about it one bit.

I also know that If you plan to beat the life out of your Jeep, it will not matter as the weakest point will fail, be it the axles, the drive shafts, or the gears.

As a good friend of mine stated, if you're hard on your stuff, you will keep upgrading as the weak spot moves around your vehicle. He is a drag racer. 1500 hp car, first it was the torque converter, then the trans, then the axle shafts then the drive shaft. His weak parts showed up after he put an additional 500hp under the hood.
 

H0tD0g

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What's the cost of 4.88 installed? I'm running 37's and the stock 4.10's and definitely see a need to re-gear. I pull a trailer at times, and rarely if ever see 8th, and even 7th.
 

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