REGEARING RUBICON WITH 3.8 & AUTO TRANS & 35s: 5:13s?

GP NOIR

GP NOIR

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How fragile are 5.13s in Rubicon D44s? The 42RLE has a 2.84 1st gear and even with a 4.0 t-case and 4.1 axle, crawl ratio is a dismal 47:1. 4th gear is .69 resulting in 1900 RPMs at 70, giving abysmal performance and gas mileage. Rolling on 35s, my brother gets 9 MPG highway. Switching to 5.13s gives a crawl ratio of 58:1 and almost 2800 RPM at 70.

In another forum, a guy said his gas mileage went to 17 MPG after installing 5.13 gears. His Jeep has the 3.8/auto on 35s.

Is the added durability of the 4.88s enough to give up the performance edge 5.13s have for the 3.8 and 42RLE? (4.88 Crawl Ratio: 55:1 RPM@70: 2379) Or is the 5.13 gear weakness exaggerated? Several 3.8 JK owners claim the 3.8 needs 5.13s for best performance with 35s.

The Jeep is a daily driver that gets wheeled- twice monthly trips to Tuttle Creek (Shale ledges, mud, loose hill climbs) and Moab once or twice a year.
 
GP NOIR said:
How fragile are 5.13s in Rubicon D44s? The 42RLE has a 2.84 1st gear and even with a 4.0 t-case and 4.1 axle, crawl ratio is a dismal 47:1. 4th gear is .69 resulting in 1900 RPMs at 70, giving abysmal performance and gas mileage. Rolling on 35s, my brother gets 9 MPG highway. Switching to 5.13s gives a crawl ratio of 58:1 and almost 2800 RPM at 70.

In another forum, a guy said his gas mileage went to 17 MPG after installing 5.13 gears. His Jeep has the 3.8/auto on 35s.

Is the added durability of the 4.88s enough to give up the performance edge 5.13s have for the 3.8 and 42RLE? (4.88 Crawl Ratio: 55:1 RPM@70: 2379) Or is the 5.13 gear weakness exaggerated? Several 3.8 JK owners claim the 3.8 needs 5.13s for best performance with 35s.

The Jeep is a daily driver that gets wheeled- twice monthly trips to Tuttle Creek (Shale ledges, mud, loose hill climbs) and Moab once or twice a year.
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My 2009 JK had 37’s, 5.13’s and the auto.

My personal experience was on road it did ok and as long as I could keep my speed up on the hills it was good. If I got trapped behind a slow car getting speed back was very difficult. I drove this Jeep across the country on I-40 several times and to and from Moab. Mileage was about 12-14 mpg except in the mountains were it was 10-12.

Off road the vast majority of my wheeling was in low range because the engine lacks torque and trying to climb anything in high range was a futile endeavor. I never had an issue with durability and the 5.13’s, but I was very careful with the skinny pedal and wheel spin.

I did replace the front axle shafts with aftermarket chromemoly when I put the ProRock 44 in it.

It did 6 & 7 rated trails in Moab with no issues and every trail I could find in AZ. I believe the 5.13’s will do fine if you avoid beating on it where the drive line loads and unloads.
 
2010 JKU, 4.88's, prorock front, 37's on ATX beadlocks, did much better with 315's not 37's.

mileage sucked with the slightest breeze, OD was a waste of a gear choice as the gearing was too high to stay in it and it would easily fall into a gear hunt episode, so it stayed locked out, even in city daily driving.

IMO the power out the 3.8L was fine, the transmission paired to it is a donkey fucking itself.
 
Get the 5.13’s. Ran them in my 11 JK for years in the stock rear with an ARB. Had 35’s then 37’s. It was a lot of gear for 35’s imo but still made the drive to Moab and back on them. With 37’s it felt more at home. It never liked to be in OD on hills but it was good imo
 
Having run 5.13s with 35's and with a 3.8L in the past, what I can tell you is that they're plenty strong in a 44. That said, I would never pretend to know as much as what some guy says on another forum but I call BS on the improved MPG. If anything, you will run on the high side of RPM at highway speeds and I personally saw LESS fuel economy. But then, that's just me.

With a 3.8L, 5.13 is best with a set of 37's
 
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wayoflife said:
Having run 5.13s with 35's and with a 3.8L in the past, what I can tell you is that they're plenty strong in a 44. That said, I would never pretend to know as much as what some guy says on another forum but I call BS on the improved MPG. If anything, you will run on the high side of RPM at highway speeds and I personally saw LESS fuel economy. But then, that's just me.

With a 3.8L, 5.13 is best with a set of 37's
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Especially at your 80 plus MPH cruising speed. 🤣
 
WJCO said:
I recognize that spot. I think i took the rubber ducky line though.
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The other line hard in its own way, though. It’s really tight and it’s difficult to turn left hard enough to take it straight on. I’ve been jammed up on that before.
 
I've got 5.38 gears on 37s. Nothing weak about them, they take abuse just fine. Makes driving on the street nice.
 
SpikesHD said:
I've got 5.38 gears on 37s. Nothing weak about them, they take abuse just fine. Makes driving on the street nice.
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While you may have found them to work well with your 37's, you'd be incorrect in saying there's "nothing weak" about them. Fact of the matter is, the pinon on a 5.38 is very very small on a Dana 44 and it IS a very weak point. Albeit, I was running 40's at the time but I personally found this out the hard way.
 
just my 2 cents, i ran 35's with the stock 3:73s for ever ( 242K) still got shit mileage ... it was habit to start the jeep and turn off the over drive . still only got about 230-250 miles per tank... it did fine in 4lo but i do wish i re-geared it.. you will only enjoy the jeep more with better gearing ...
 
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