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Going to 4.88 or 5.13 for 37s?

CarbonSteel

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Completely agree, 2500 is fine. I see people complaining about that and don't get it. As you mentioned, did not buy it for MPG. Also, 5.13 gave me some extra pep off the line and are great for crawling.
Yep; agreed. If it were 2500 @ 55MPH it may be a different conversation, but it is 75MPH. With the exception of a few would be race car drivers sitting in the wrong vehicle, I would opine that most here see 75-80MPH as their "top" speed, despite what the Jeep can actually run.
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I run 4.88 with Milestar Patagonia 38s. It doesn't take much of a head wind to get me out of 8th gear.
 

roaniecowpony

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I've driven my 37s/4.88 setup a few hundred miles now. Saturday, I put a couple hundred on it going from L.A. up the Grapevine (I-5) to Frazier Park and back (sea level to about 4400 ft) then on into Lockwood Valley which is a narrow curvy road up to about 4800 ft elevation. It was a good trip to get familiar with how the lift/37s/4.88s affected my 3.6L/auto JLUR. The freeway takes you up a steep grade for about 7-8 miles and then it's a mix of ever changing grade angles, while mostly climbing to higher altitude. There's also the wind factor during this time of the year. Wind was maybe 10-15 mph against me going uphill.

I had driven this in the stock JLUR configuration. It was surprisingly peppy, but used the gears during the steeper sections while going in the 70s mph.

When I traveled it Saturday with the lift, tires and gears, it was noticeable that it would hold 7th and even 6th gear for long sections, rarely going into 8th gear on the way north (uphill against the wind). On the way back south, it held 8th gear almost all the way.

I haven't taken it on any trails yet. But numerically, it should be slightly higher rpm for the same speed than my factory 4.10/33s.

So far, I'm pleased with my choice of 4.88s with the 37s.
 
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kapk22

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I've driven my 37s/4.88 setup a few hundred miles now. Saturday, I put a couple hundred on it going from L.A. up the Grapevine (I-5) to Frazier Park and back (sea level to about 4400 ft) then on into Lockwood Valley which is a narrow curvy road up to about 4800 ft elevation. It was a good trip to get familiar with how the lift/37s/4.88s affected my 3.6L/auto JLUR. The freeway takes you up a steep grade for about 7-8 miles and then it's a mix of ever changing grade angles, while mostly climbing to higher altitude. There's also the wind factor during this time of the year. Wind was maybe 10-15 mph against me going uphill.

I had driven this in the stock JLUR configuration. It was surprisingly peppy, but used the gears during the steeper sections while going in the 70s mph.

When I traveled it Saturday with the lift, tires and gears, it was noticeable that it would hold 7th and even 6th gear for long sections, rarely going into 8th gear on the way north (uphill against the wind). On the way back south, it held 8th gear almost all the way.

I haven't taken it on any trails yet. But numerically, it should be slightly higher rpm for the same speed than my factory 4.10/33s.

So far, I'm pleased with my choice of 4.88s with the 37s.
I have the 2.0 liter and my tires are closer to true 37”. I checked with a local shop in San Antonio for a quote on 5.13s and they said I would be running higher rpm’s during normal driving and would lose fuel economy. I would love to save on fuel, but that’s not a big concern for me. I am more worried about my transmission being damaged by having the tires I have on her and not gearing. There have been a handful of people saying the transmission will go out much faster if I don’t change the gearing. If going to 4.88s gets me back/closer to what it was stock with the factory tires, I would think it would be a better choice now.
 

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TylerV76

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I have the 2.0 liter and my tires are closer to true 37”. I checked with a local shop in San Antonio for a quote on 5.13s and they said I would be running higher rpm’s during normal driving and would lose fuel economy. I would love to save on fuel, but that’s not a big concern for me. I am more worried about my transmission being damaged by having the tires I have on her and not gearing. There have been a handful of people saying the transmission will go out much faster if I don’t change the gearing. If going to 4.88s gets me back/closer to what it was stock with the factory tires, I would think it would be a better choice now.
Im running KO2’s with 5.13’s with the 2.0 and at 75mph Im at 2200 rpms. I am getting 19.2 mpg right now with winter blend and winds the past week or so in the low teens.
 
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kapk22

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Im running KO2’s with 5.13’s with the 2.0 and at 75mph Im at 2200 rpms. I am getting 19.2 mpg right now with winter blend and winds the past week or so in the low teens.
Holy Crap!! I think the best mpg I got during the 2400 mile trip was 17.7. That’s with stock 4.10s. Usually get around 14.5 around town. The mud grapplers are definitely different though.
 

TylerV76

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Holy Crap!! I think the best mpg I got during the 2400 mile trip was 17.7. That’s with stock 4.10s.
Im mostly highway or 55mph back roads. Plus Michigans pretty flat. But yeah Im happy with those numbers. Really happy with the 5.13’s.
 
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Im mostly highway or 55mph back roads. Plus Michigans pretty flat. But yeah Im happy with those numbers. Really happy with the 5.13’s.
Which gears did you get? I’m leaning toward these after others have strongly recommended,,,

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I have Yukons, theyre awesome. The installer has to be good. They say Nitro are better but my yukons have been great. I don't rock crawl for a LIVING so :)

I've dropped fluid a few times now in 10k miles and the first swap was at 2500.. it was pretty dark, then again at 7000 it was almost clear so they broke in pretty good and will last me 100k miles.. no gear whine and clear fluid.
 
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kapk22

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I’ve been reading that gearing will definitely void my warranty, at least for the axles. Would having 37s alone void my warranty if I ended up having problems with my stock axles within the warranty timeframe?
 

roaniecowpony

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I’ve been reading that gearing will definitely void my warranty, at least for the axles. Would having 37s alone void my warranty if I ended up having problems with my stock axles within the warranty timeframe?
Good question.
"voiding the warranty" is a kinda squishy thing. A dealership can deny coverage of an issue based on his determination of that cause. If your modifications lead them to believe it was the cause, they will likely deny coverage of that issue. Apparently, they can make an entry in an FCA database for your vehicle history, indicating the denied coverage and the reason.

But to "void the warranty" blanketly across the whole vehicle...that would have to be for something that was pretty extreme. Something like the vehicle being totaled and then salvaged (salvage title) might be reason enough.

For your gear change, I'd just count on Jeep not honoring warranty on the axles, flange to flange, unless the dealership did the work and they have their own warranty for work they do. But at what cost by going to a dealership for that work?

For the tires, that could get into a real debate. But, the bottom line is that they put a lot more stress on the entire driveline. If you break a driveshaft or trash the transmission or transfer case, you could be on your own.

You have to be ready for the worse case when modifying a vehicle still under warranty.
 
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kapk22

kapk22

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Good question.
"voiding the warranty" is a kinda squishy thing. A dealership can deny coverage of an issue based on his determination of that cause. If your modifications lead them to believe it was the cause, they will likely deny coverage of that issue. Apparently, they can make an entry in an FCA database for your vehicle history, indicating the denied coverage and the reason.

But to "void the warranty" blanketly across the whole vehicle...that would have to be for something that was pretty extreme. Something like the vehicle being totaled and then salvaged (salvage title) might be reason enough.

For your gear change, I'd just count on Jeep not honoring warranty on the axles, flange to flange, unless the dealership did the work and they have their own warranty for work they do. But at what cost by going to a dealership for that work?

For the tires, that could get into a real debate. But, the bottom line is that they put a lot more stress on the entire driveline. If you break a driveshaft or trash the transmission or transfer case, you could be on your own.

You have to be ready for the worse case when modifying a vehicle still under warranty.
Makes sense. Thank you

I really don’t do any serious wheeling, rock crawling. Now that I am in Texas, I still have to research where to play. I joined a local club on Facebook and hope to get together with some people soon. It’s definitely a different terrain here, especially the soil (clay). Like I mentioned before, I am mainly concerned with the wear my 37s are causing on the transmission. It would make sense that the driveshaft and brakes would take a beating as well. I have added adjustable track bars and adjustable control arms (Clayton’s in the rear and rough country for the lower fronts). The lift is the 2” Mopar Fox and I am starting to rub on the rear plastic over big bumps (probably just going to trim that plastic liner a little).

If going to 5.13s will prevent premature damage to costly components, it would seem to be a no brainer. However, it seems I may need to research a bit more to really understand this.
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