JLUR on 37s regear 4.56 or 4.88

offcamber

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Same here in flat Texas. Drove me crazy. Was gonna regear, but decided to step back down in tire size instead. Stays in 8th better now. 285/75 Ridge Grapplers. Still good for the trails this Jeep will see.
You guys must have something wrong. I'm on 37's with 4.10's and mine is fine. I go into 8th on the highway. Honestly it feels like my JK did with 4.88's.





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You guys must have something wrong. I'm on 37's with 4.10's and mine is fine. I go into 8th on the highway. Honestly it feels like my JK did with 4.88's.
Nope, Jeep is fine. I drove a 4 door Rubicon on 37’s and 4.10’s too. Couldn’t have lived with it either, would have done 4.88’s. Personal preference I guess.
 

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You guys must have something wrong. I'm on 37's with 4.10's and mine is fine. I go into 8th on the highway. Honestly it feels like my JK did with 4.88's.
I installed 37's and a 3.5" lift last week.

I'm on stock gears, for now. I have the 4.88's in the garage waiting for the time to install.

I will say that, even with the 6-speed, that it's definitely daily drive-able. 6th gear is almost useless unless you're on flat interstate at 75+ mph, but everything around here where I live is actually ok. You can tell the Jeep is slower down low, but it has plenty of power to turn the 37 with 4.10's.

I'm re-gearing to get everything back to the way it should be with power down low and, of course, the off road performance. If it takes me another month to find the time to re-gear, I'm not too worried about it. The Jeep handles the 37's well.
 

offcamber

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Nope, Jeep is fine. I drove a 4 door Rubicon on 37’s and 4.10’s too. Couldn’t have lived with it either, would have done 4.88’s. Personal preference I guess.
I guess so. My Jeep does 0-60 in under 8 seconds. My JK on 35's with 4.88's did it in about 8.2 seconds. I get 19 mpg on the highway, which is about 4 mpg better than my JK did. Thats pretty livable to me.
 

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I'm on 37s with the mopar 2" lift and 4.10s

Mine will not go into 8th on the highway, I've tried running at 70, 75, and 80, and at best it hits 7th but often will sit in 6th.

I used the tazer JL to change the tire size and the speedo it true to GPS speed but the transmission just doesnt feel right.
 
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I’m in the middle of a gear swap. 35” tires and 5.38 gears. I’ll post up when I’m done. The 8th gear is so tall you can get away with a higher gear.

Stock @ 70mph in 8th....1975rpm
Stock @ 70mph in 7th....2476rpm
35’s at 70 w/5.38 gears.....2422rpm

The motor will be turning less with the 5.38 and 35” tires than if you ran stock in 7th gear. For all those that have lost their 8th gear due to larger tires, don’t go to shallow on your gear selection.

Since upgrading to 35” tires the only time that I see 8th gear is on a downslope with a tail wind. May as well have a vehicle that is able to use all 8 gears rather than effectively reduce the capabilities of the vehicle to 7 gears.
Hey man,

I'd love to hear your review on the 5.38's after re-gearing and driving around on them. What are your thoughts here?

You're an auto right?
 

Petey003

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I'm on 37s with the mopar 2" lift and 4.10s

Mine will not go into 8th on the highway, I've tried running at 70, 75, and 80, and at best it hits 7th but often will sit in 6th.

I used the tazer JL to change the tire size and the speedo it true to GPS speed but the transmission just doesnt feel right.
Hey Man!

I'm in a similar boat as you and pretty sure I'm gearing to 4.88's next week! I posted a thread about it all including a breakdown of my rpms at 65, 70, 75, and 80mph with my 4.10's and 37s. It feels like a terd in the mountains! Wouldn't be so bad on flat land but I'm always in mountains in the north east.

You ever re-gear? If so, what did you do?
 

JudHumphries

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I just got my Jeep (JLU Sport S Manual trans) back after re-gearing to 4.56. Feels a lot better. I have 5th and 6th back. BUT!!!! My auto start/stop light come on and stops working when I put it in 4th, and my reverse camera doesn't work in reverse when the light is on. Also, the Hill Assist doesn't work. I took it back the the shop and they told me they didn't have the ability to reprogram the JL.They believe reprogramming it should work.
 

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I just got my Jeep (JLU Sport S Manual trans) back after re-gearing to 4.56. Feels a lot better. I have 5th and 6th back. BUT!!!! My auto start/stop light come on and stops working when I put it in 4th, and my reverse camera doesn't work in reverse when the light is on. Also, the Hill Assist doesn't work. I took it back the the shop and they told me they didn't have the ability to reprogram the JL.They believe reprogramming it should work.
Did you update with super chips or taser JL
 

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I just got my Jeep (JLU Sport S Manual trans) back after re-gearing to 4.56. Feels a lot better. I have 5th and 6th back. BUT!!!! My auto start/stop light come on and stops working when I put it in 4th, and my reverse camera doesn't work in reverse when the light is on. Also, the Hill Assist doesn't work. I took it back the the shop and they told me they didn't have the ability to reprogram the JL.They believe reprogramming it should work.
I had the exact issue after installing my 488's. Follow the directions on this document I got from a local dealer. It has worked for several of us!
 

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Speedy3

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19 JLU Rubi auto here, with a heavy 37" wheel and tire setup. I'm in hilly NJ and never got into 8th on the highway at 75 or so. She would hunt between 6th and 7th. I went 5.13's and wouldn't change it for a thing. I was averaging 15-16 mpg before the gears and it didn't seem to change much, maybe 1 mpg.
 

Amelia18

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http://www.grimmjeeper.com/gears.html
You can use this calculator and it will tell you everything. It took me a couple of times to figure it out but, it was very help full. I’m in southern Oregon running 37’s and the 4.10 don’t due bad. It’s just not that great either. I’m going to go 4.88 or 5.13’s.
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.
 

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New member here, and I gotta say that this is a great community, and I really appreciate folks sharing their experiences. I'm getting ready to pull the trigger on a 2019 Rubicon Unlimited, 6-speed. I'll be coming from a 2017 Tacoma 6 speed (manual transmission), and I'm a little worried about moving from one low-torque, high revving engine, to another. Having said that, the Jeep 3.6 is much better than the Tacoma 3.5 - not just stronger but the power is also more linear. The Tacoma almost feels boosted, because when it shifts from Atkinson to Otto cycle you get this weird power surge (around 3500 rpm). Under 3500 rpm there is no torque, and waiting for the power to come isn't fun. In my limited experience test-driving a bunch of different JLURs (including an 8-speed on 35s with a 2-inch Mopar lift) the Jeep engine has much better low-end torque than the Tacoma. I'm pretty excited for a JLUR on 35s! But I do think it will need gears.

Anyone out there driving in the mountains in a 6-speed on 35s? From what I'm reading on this forum, it seems like experiences really vary depending on whether people are mostly driving flatter roads around sea-level, or if they are up at higher elevations. My commute takes me from 8,500 feet down to 5,500 feet (and back up at the end of the day). I also drive over the high passes regularly (10-11,000 ft). I was planning on going to 4:88 with the 6-speed and 35s, but I want to get it right. Right now (on stock 4:30 gears in my MT Tacoma) I can't get out of first gear going up dirt roads to trail heads. I really don't want a similar issue with the Jeep. Yeah, I could re-gear the Tacoma, but after 30 years driving a truck, I'm ready for a Jeep! Anyway - sorry for such a long post. Any advice is much appreciated!
 

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Talked with local shop that does gear changes daily. 4.88's for 37's for most DD/WW. Said they only recommend 5.13's for guys that are going to wheel a ton on the hard stuff. Each their own on running 37s on 4.10s. It sucks. Tolerable but sucks. So much time is spent in 4th, 5th and 6th on the highway. Doesn't take much of an uphill grade or head winds and it stays in 5th or 6th. Just got back from Moab. I'm doing 4.88s next month and look forward to seeing 7th and 8th more often. Just waiting for the holiday sales to kick in so I can pick up a good deal on new diff covers to go on at the same time.
 

Petey003

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Hey All!

I wanted to give an update to my experience in my 2018 JLURubicon. I went from the stock 4.10 gears to Dana Spicer 4.88 gears. All I have to say is WOW!

Weight/Build Notes: Stock weight was roughly 4,430lbs. Current weight with full tank, bumpers, sliders, tires, tools, full RotoPax, fridge, etc is 5,370. I stopped and weighed my Jeep at the CAT scales at a Pilot Truck Stop. Also on 37’s (82lb General Grabber X3’s) and Rock Krawler X Factor 2.5” lift. +940lbs heavier since stock

I was really feeling the weight add on the highway often losing 8th and sometimes 7th gear. I’m also in the New York City area and spend a lot of time in and out of mountains (VT, NH, NY).

I almost went 4.56 gears to maintain gas mileage when not in the hills but due to all the time I spend in the mountains I went with the 4.88’s. I also may go with 38’s on my next set of tires so I wanted to future proof in case I make that move.

Review: LOVE. I couldn’t be happier with the extra power! I have a breakdown of RPM’s at 65, 70, 75, and 80mph listed below. The engine is much quieter

MPG: 80mph on cruise control gets around 19.4-7mpg which is amazing. With stock gears I was stuck in 6th gear a lot on the highway so my mileage went up by about 1mpg. I’m getting 22.1-7mpg around 60-63Mph on cruise control! As good or better than stock set up.

Lastly, I’ve heard about people losing Start/Stop and other errors. I have the SuperChips programmer and was able to be at the shop upon completion of the gears. Before I ever rolled the Jeep out of the rack I reprogrammed my gears to the 4.88’s I haven’t had any problems whatsoever. So that’s my recommendation on that, don’t let your Jeep move until reprogrammed! I think 4.56’s would have been fine if I only did tires without all the extra weight but with my added weight/build I am so happy I went with the 4.88’s!

Thanks everyone!

Follow me and check out my build @ PETEY003 on instagram! I’ll answer questions there!
 

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