5:38 gears questions - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 45 Old 11-11-2018, 10:21 AM Thread Starter
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5:38 gears questions

Anyone have experience running 5:38s and 35s? Itís my partial daily driver at least my favorite to drive. I will eventually be going to 37s but donít want to regear 2 times. Just curious how it drives with those gears and 35s. My Jeep is an automatic 2008 Rubicon . I purchased a snorkel to have a true cold air intake along with a trail dash 2 for tuning and dual exhaust. Any other mod recommendations would be appreciated also. It will continue to a partial daily driver. Iím not a mall crawler or pavement princess lol. We currently have a 2004 rubicon with 35s and 4:88s that we rock crawl In and the 2008 rubicon that we be used on mild trails.


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post #2 of 45 Old 11-11-2018, 12:45 PM
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(No experience with 5:38s but at least some input) I have 5:13s and 37s on my 08 JKUR. I run the highway at 65mpr and like 2200+/- rpms. Any faster and I find it down shifting on the siltiest incline. 5:38s would definitely work better for the 37s and 3.8L. I only went with the 5.13s for a little more strength in the pinion. I don’t mind going 65. If your planning to upgrade to 37s not too long after the 5:38 install, I don’t think it will be a problem. Just running higher rpms for the time being.

As for upgrades, a tuner or procal is a must, just to tell the computer of the gear/tire change. Other then that everything is just to get a little better “performance” out of the motor. I run a K&N drop in air filter w/ stock air box to keep any water out, a flowmaster cat back exhaust, and a bully dog tune. I also try not to run higher then 3K rpms going up steeper mountain passes on the highway. That way the little slug of a motor isint stressed too much.
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post #3 of 45 Old 11-11-2018, 05:28 PM
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I would be wary of 5.38s on a D44. The pinion gets awfully small. It's a better match for 37s for sure, but I wouldn't recommend anything deeper than 5.13s unless you're running 60s.

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post #4 of 45 Old 11-11-2018, 06:43 PM Thread Starter
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Then Iíll probably just go with 5:13s.


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post #5 of 45 Old 11-11-2018, 06:46 PM
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5:13s with the 35s will feel great. You won’t want to go up to the 37s lol. I have tossed around the idea of swapping out my buddies 35s for the day just to see how much better it das
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post #6 of 45 Old 11-11-2018, 07:07 PM
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I ran 35s for 6 months on 5.13s before getting my 37s. They are perfect for 35s. They lose a little highway manners with the 37s, but still great. Like I said before, when I go to 60s I'll do 5.38s, but until then, I'm really happy with them.

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post #7 of 45 Old 11-11-2018, 07:10 PM
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Yeah 5.38s in a 44 is just asking for trouble. Stick to 5.13s.
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post #8 of 45 Old 11-11-2018, 07:15 PM Thread Starter
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Thanks for all in info guys.


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post #9 of 45 Old 11-11-2018, 08:45 PM
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2008 JKU auto. I was running 5.13's with 35's, then changed to 5.38's with the 35's (as part of a PR44 swap and redid the rear), and a year and a half later or so went on up to 37's.

Not a huge difference between the two ratios, 120 rpms or whatever it is at freeway speeds. Not 'screaming high' rpm as some folks like to report, and certainly won't be confused with having the power of a v-8, but I liked the slightly higher rpms. Held freeway speeds better, and kept me in overdrive that little bit longer before downshifts.

The only negative I found was that I prefer to tow my boat OD/Off. So long freeway trips would either have me worried about the trans in OD, or going slow with it off.

From a strength perspective, dunno. Lots of fear-mongering on the boards, but I really haven't seen any gear issues reported where someone could say "it happened with X ratio, but it definitely would not have happened if I had been running a single numerical ratio lower!" Not an engineer or a mathematician, but I don't imagine there is a huge strength difference between those two ratios in a JK D44?
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post #10 of 45 Old 11-11-2018, 08:54 PM Thread Starter
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my reasoning for regearing is to keep as little stress as possible off of my engine and transmission. I just broke 100k on the engine. I stay on top of maintenance to try and keep them healthy.


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post #11 of 45 Old 11-12-2018, 03:42 PM
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I have run 5.38s on a 3.8 and now a 3.6 both automatic Rubicons (one ton axles and running 40" tires) I think you could potentially get away with 5.38s for a short time, but not for long.

You could try using a tuner to help change shift points and performance a bit to accommodate the tire size for the time being. I had 5.13s before on my JK on 37s and it worked pretty well.

One more factor to consider, the pinion size on the 5.38 gears so keep that in mind.
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post #12 of 45 Old 11-12-2018, 04:34 PM
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Been running 5.38ís on my Ď07 6 speed manual for the last 4 1/2 years with no problems related to the pinion. Ran on 35Ē Nitto Trail Grapplers up until April of this year when I jumped up to 37Ē Nitto Trail Grapplers and beadlocks. I turn around 3100 rpms between 70-75mph. Great street manners with the 37ís, as well as off-road. Itís all in how you drive off-road. Iíve seen stock pinion gears, ring gears, and spider gears fail on stock Jeeps. If Iím crawling and I start to bounce, Iím immediately out of the throttle. I just back up and try to take a better line, or get a little more of a running start. With my manual trans, Iím happy with 1st gear in low. Non Rubi by the way, but fully built Rubi axles.

Current vehicles:
2007 Sahara 2-Door
5.38 gears
Trussed, sleeved, gusseted Dana 44 front w/ factory Rubi locker and RCV shafts
Stock rear Rubi Dana 44 with Auburn Ected locker w/ 35 spline chromoly shafts
6 Speed
2.5 Rock Krawler X Factor System w/ Bilstein 5100 shocks
17X9.5 Spyderlock Beadlocks
37X12.50R17 Nitto Trail Grapplers
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JCR Stage 2 rock rails
Warn Zeon 10-S winch

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post #13 of 45 Old 11-13-2018, 02:49 PM
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Well, I've run my 5.13's for about 30k miles and finally busted a couple of rear pinion teeth. I completed the trail that day and aired up. It wasn't until I pulled out onto the highway that I heard the knocking noise increasing with vehicle speed. Rode home on a flatbed that day and even with the 100 miles included with AAA, that was a $400 ride home. No clue as to exactly where on the trail it broke so I can say that I had fun doing it!

I have a manual transmission, 37s on beadlocks, and a supercharged pentastar.

I am about to order wontons - most likely pretty much totally guaranteed to be UD60s. Those will be high pinion (weaker than low pinion on the rear) and 5.38's. Plus as part of that we beef up the drive shafts from 1310 to 1350.


YES! Another Indian scammer called me while typing the response. 207-263-1035. My SSN was compromised. Of course, I fugged with him. Mader chod.
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post #14 of 45 Old 11-13-2018, 02:51 PM Thread Starter
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Quote:
Originally Posted by White13JKUR View Post
Well, I've run my 5.13's for about 30k miles and finally busted a couple of rear pinion teeth. I completed the trail that day and aired up. It wasn't until I pulled out onto the highway that I heard the knocking noise increasing with vehicle speed. Rode home on a flatbed that day and even with the 100 miles included with AAA, that was a $400 ride home. No clue as to exactly where on the trail it broke so I can say that I had fun doing it!



I have a manual transmission, 37s on beadlocks, and a supercharged pentastar.



I am about to order wontons - most likely pretty much totally guaranteed to be UD60s. Those will be high pinion (weaker than low pinion on the rear) and 5.38's. Plus as part of that we beef up the drive shafts from 1310 to 1350.





YES! Another Indian scammer called me while typing the response. 207-263-1035. My SSN was compromised. Of course, I fugged with him. Mader chod.


Bawhahaha getíem!!!! Thanks for you input.


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post #15 of 45 Old 11-13-2018, 03:29 PM
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post #16 of 45 Old 11-13-2018, 04:02 PM
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I ran 5.38 on 37's for about 6 years without issue. I first broke a rear ring and pinion towing a small ski boat to the lake not far from home. Then I'd randomly brake a rear ring and pinion every 6 months afterward. The third time, the ring bolts backed out and completely sheared off, grenading the rear axle from inside.

I got tired of axle issues and got the Dynatrac XD60/D80. Not only are these things beef, but the steering characteristics are way better on the trail (more turn radius and no bind in turning when locked.)
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post #17 of 45 Old 11-13-2018, 04:04 PM Thread Starter
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Quote:
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I ran 5.38 on 37's for about 6 years without issue. I first broke a rear ring and pinion towing a small ski boat to the lake not far from home. Then I'd randomly brake a rear ring and pinion every 6 months afterward. The third time, the ring bolts backed out and completely sheared off, grenading the rear axle from inside.



I got tired of axle issues and got the Dynatrac XD60/D80. Not only are these things beef, but the steering characteristics are way better on the trail (more turn radius and no bind in turning when locked.)


Thanks bud


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post #18 of 45 Old 11-13-2018, 04:09 PM
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Quote:
Originally Posted by TJT View Post
I ran 5.38 on 37's for about 6 years without issue. I first broke a rear ring and pinion towing a small ski boat to the lake not far from home. Then I'd randomly brake a rear ring and pinion every 6 months afterward. The third time, the ring bolts backed out and completely sheared off, grenading the rear axle from inside.

I got tired of axle issues and got the Dynatrac XD60/D80. Not only are these things beef, but the steering characteristics are way better on the trail (more turn radius and no bind in turning when locked.)
What axle width do you have and what is your wheel back spacing?
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post #19 of 45 Old 11-14-2018, 11:48 AM
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5.38 in a D44 is just way to small. I shredded two sets in 6 mos before switching to a D60.
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2011 Jeep Rubicon JKU 6.0l VORTEC L96 - 6L80E 6 speed auto
40" Cooper SST Pros-17" Level 8's - 4.5" Synergy Suspension
WTO Hydro assist- Fusion D60's 4.88 gears
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post #20 of 45 Old 11-14-2018, 01:21 PM
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5.38 in a D44 is just way to small. I shredded two sets in 6 mos before switching to a D60.
Which D60 do you have? A top pinion or bottom pinion?
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post #21 of 45 Old 11-14-2018, 03:07 PM
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Quote:
Originally Posted by Riptide9 View Post
5.38 in a D44 is just way to small. I shredded two sets in 6 mos before switching to a D60.

2011 Jeep Rubicon JKU 6.0l VORTEC L96 - 6L80E 6 speed auto
40" Procomp MT2-17" Level 8's - 4.5" Synergy Suspension
WTO Hydro assist- Fusion D60's 4.88 gears
VKS Fab and XRC Bumpers/Armor-9500 Synthetic Winch 10lb CO2-Teraflex Big Brake Kit
360ish HP and 40" tires vs a 3.8 and 35's. Doesn't seem to be a very fair comparison regarding gear strength/longevity.
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post #22 of 45 Old 11-15-2018, 12:42 PM
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Exactly
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post #23 of 45 Old 11-15-2018, 01:30 PM
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Quote:
Originally Posted by White13JKUR View Post
Which D60 do you have? A top pinion or bottom pinion?
Bottom pinion on the D60
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2011 Jeep Rubicon JKU 6.0l VORTEC L96 - 6L80E 6 speed auto
40" Cooper SST Pros-17" Level 8's - 4.5" Synergy Suspension
WTO Hydro assist- Fusion D60's 4.88 gears
VKS Fab and XRC Bumpers/Armor-9500 Synthetic Winch 10lb CO2-Teraflex Big Brake Kit
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post #24 of 45 Old 11-15-2018, 01:41 PM
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Quote:
Originally Posted by GreenJK View Post
360ish HP and 40" tires vs a 3.8 and 35's. Doesn't seem to be a very fair comparison regarding gear strength/longevity.
The point is there is a big strength difference between a 4.88 pinion and a 5.38 one. The 5.38 is the smallest pinion you can stick in the 44 and I think the better choice for 37's would be the 4.88 for drivability and strength.

The picture is of a D44 3.21 and the tiny 4.88 to see the similar proportions... Now imagine how much smaller the 5.38 would be, even the weak 3.8 could break it with 37's pretty easily
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2011 Jeep Rubicon JKU 6.0l VORTEC L96 - 6L80E 6 speed auto
40" Cooper SST Pros-17" Level 8's - 4.5" Synergy Suspension
WTO Hydro assist- Fusion D60's 4.88 gears
VKS Fab and XRC Bumpers/Armor-9500 Synthetic Winch 10lb CO2-Teraflex Big Brake Kit
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post #25 of 45 Old 11-15-2018, 01:51 PM
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One other consideration that should be part of your decision is , as you increase your driveshaft speed you can and will encounter harmonics that can be detrimental to your transfercase's wellbeing .

Those that have upgraded to 60's have put this in their rearview mirror but , there has been reports of extensive damage to a number of JK's , mostly those that thought that the vibration was normal or somewhat so .
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