3.6L, 8 AT, 37”: 4.88 or 5.13?

TJP

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Went 4.88 on 37” bfg ko2 (35.5 actual) in rubicon v6. Very happy w it.
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tjeeper

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Picked up my JL today, had 5.13s installed. On the drive home, going 50mph it was in 8th. Weird. Haven't seen that since stock. Something else- I have a very steep driveway. The only way I could go slowly up after stopping is to load the torque converter until it has enough power to move and go forward. Now I can drive up the driveway normally.

I'll report back when I have some mileage on it with mpg and how it performs on the highway.
 

JeepinJason33

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I ended up going with the 5.13’s. Thank you to everyone that pushed me in that direction. 8th gear RPMs are fine and I am able to hold 8th better now than before the extra weight of the lift and tires! The acceleration is also much better off the line. I am sure it will take something away on the top end, but I hit 85 mph yesterday without any problem and I doubt I will ever need to go faster than that. Also loaded it up with the entire family and some junk and had no problem maintaining 75 mph, which is the speed limit here in Denver.
 

Gadgettr1

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I ended up going with the 5.13’s. Thank you to everyone that pushed me in that direction. 8th gear RPMs are fine and I am able to hold 8th better now than before the extra weight of the lift and tires! The acceleration is also much better off the line. I am sure it will take something away on the top end, but I hit 85 mph yesterday without any problem and I doubt I will ever need to go faster than that. Also loaded it up with the entire family and some junk and had no problem maintaining 75 mph, which is the speed limit here in Denver.
What was the total cost to swap the gears? What are your "real world" rpms at 75 and 85mph?
 

JeepinJason33

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Nearly 3k total including 500 mile checkup and fluid swap.
2300-2400 at 75 mph. 2600-2700 at 85. This is at 5500’ elevation.
 

Tdog495

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Posted a couple months back that I gotten 4:88’s, well I ended up regretting it and now I have 5:13. Night and day. Best thing about 5:13 is that it just hold the gears stronger. 4:88’s was struggling to hold even 6th gear on a slight hill. Smh .. 5:13 would keep that same gear and hold it strong
 

JeepinJason33

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Posted a couple months back that I gotten 4:88’s, well I ended up regretting it and now I have 5:13. Night and day. Best thing about 5:13 is that it just hold the gears stronger. 4:88’s was struggling to hold even 6th gear on a slight hill. Smh .. 5:13 would keep that same gear and hold it strong
I really struggled back and forth on this as well. I had shops pulling me both directions and went with 5.13's. Sucks you had to pay twice!
 

Tdog495

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I really struggled back and forth on this as well. I had shops pulling me both directions and went with 5.13's. Sucks you had to pay twice!
Yeah for real. I just couldn’t take it anymore. The 4:88’s was driving me nuts. Was tired of the downshifts, and the car felt heavy. Now I love the car again. Yesterday I drove all the way home on 8th gear. With the 4:88’s I would be between 6th -8th, in and out
 

Marman

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The questions I have for those with 3.6L engine, automatic transmission, and 37” tires:
  • Did you regear to 4.88 or 5.13 gears?
  • Do you regret your choice and wish you’d selected another ratio?
  • What do you like most and least about your new gear ratio?
  • Anything in hindsight that you wish you’d known beforehand?
I care about having 8th gear back on the highway. My off-roading is usually crawling on rocks, not slogging through mud or blasting through the desert over dunes.
Have you decided on what gears your going with? I am in the same boat right now and looking at the 5.13s.
Thanks
 

dlporter

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I’ve had both. Initially went with 4.88s. Had to have both diffs redone due to a poor setup when I came to the realization that the initial installer wasn’t as good as he made himself out to be. I went with 5.13s when I had them redone and hands down prefer them over the 4.88s. I have a 3.6L w/ 8 speed AT and 37s.
 
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I’ve had both. Initially went with 4.88s. Had to have both diffs redone due to a poor setup when I came to the realization that the initial installer wasn’t as good as he made himself out to be. I went with 5.13s when I had them redone and hands down prefer them over the 4.88s. I have a 3.6L w/ 8 speed AT and 37s.
Other than the initial poor install of the 4.88, why do you prefer the 5.13?
 

dlporter

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Other than the initial poor install of the 4.88, why do you prefer the 5.13?
It definitely holds gears better than it did with 4.88s. It’s not too much of a difference, but I appreciate the little extra boost in crawl ratio when I’m in 4Lo. It’s kind of hard to describe it, but the transmission just feels “happier” with the 5.13s than the 4.88s.
 

Jeepnutz

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On a 2020 JLU Rubi w/37 Trail Grapplers and Nomad wheels I ran 4.88 for 5k miles or so and then switched to 5.13's. I already have 5.13 gears waiting to be installed when my 2022 Rubi XR arrives. If the V6 had decent torque 4.88's would of worked but unfortunately it doesn't.
 

Coolbaldguy

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On a 2020 JLU Rubi w/37 Trail Grapplers and Nomad wheels I ran 4.88 for 5k miles or so and then switched to 5.13's. I already have 5.13 gears waiting to be installed when my 2022 Rubi XR arrives. If the V6 had decent torque 4.88's would of worked but unfortunately it doesn't.
just when I thought I had made up my mind to go 4:88...now I am rethinking it.
 
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