5.38s with 37s

[TheRealGinjaNinja]

I just dropped off my Mojave on 37s to have 5.38s installed! To say I am stoked is an understatement as I have been putting this off for a while.

I wanted to start this thread to hopefully serve as a reference for others getting gears done since most of what I could find relates to 4.88s and 5.13s. I think for most people running 37s, no question 5.13s are a fantastic option and in my opinion, much better choice compared to the 4.88s. The 5.38s will certainly be a bit more aggressive than 5.13s, but considering where I live and my driving habits they should be amazing. Looking forward to posting updates!

Background
I live in the mountains outside of Seattle so any time I leave the house, I have a 1000'-1200' elevation change. I do not have the lightest setup in the world so with the 37s and stock gears it is obviously less than ideal even on flat ground. It runs pretty good in 7th gear at 2,400 rpm at 75 mph and 2,500 at 78 mph, which is what I generally cruise at. Between 68 - 72 mph it sucks because it has to drop to 6th to maintain and I am up into 2,700-2,800 rpms. So...my goal is to bring the rpms to ~2,500 rpm in 8th gear at 75 mph and under ~2,600 or less at 78. I would have to get above 80 mph to hit the high oil pressure transition and honestly, 78 is the fastest I ever go...we are driving a brick with big tires.

With that said, I want to capture the following information as I am able to obtain it and hopefully it helps others with gearing decisions:

Current Setup:

• 2021 Gladiator Mohave - 8 spd Auto
• 17x8 solid steel wheels (39 lbs each)
• 37x12.5 Mickey Thompson Baja Boss M/T (79 lbs each)
• Stock 4.10 gears
• 2" AEV lift
• ACE Pro Series front stubby / stinger 1/4" steel bumper
• Expedition One rear 3/16" steel bumper
• Expedition One steel sliders / steps
• 2.5ton steering (RPM)
• Softopper

Current Data:

• Miles Driven -
  • Stock wheels / tires - 450 miles
  • Heavy 35's - 3,160 miles
  • Current Steel Wheels and 37s - 3,655 miles
• Average mpg - 13.0
• Best mpg - 14.8
• Worst mpg - 10.9 (twice, once in November and once in July)
• 0-60 - 9.26 seconds
• Observed rpm's @ 80 mph
  • 6th gear - 3,000
  • 7th gear - 2,550
  • 8th gear - 2,000 (cannot maintain speed on flat ground)
• Observed rpm's @ 75 mph
  • 6th gear - 2,850
  • 7th gear - 2,400
  • 8th gear - 1,900 (cannot maintain speed on flat ground)
• Observed rpm's @ 70 mph
  • 6th gear - 2,650
  • 7th gear - 2,225 (barely maintains speed on flat ground)
  • 8th gear - 1,750 (cannot maintain speed on flat ground)
• Observed rpm's @ 65 mph
  • 6th gear - 2,450
  • 7th gear - 2,050 (cannot maintain speed on flat ground)
  • 8th gear - 1,650 (cannot maintain speed on flat ground)

Data with 5.38 and steel wheels:

• Average MPG - TBD
• Best MPG - TBD
• Worst MPG - TBD
• 0-60 - TBD
• Estimated (will update with actuals) rpm's @ 80 mph
  • 6th gear - 3,975
  • 7th gear - 3,350
  • 8th gear - 2,650
• Estimated (will update with actuals) @ 75 mph
  • 6th gear - 3,725
  • 7th gear - 3,100
  • 8th gear - 2,500
• Estimated (will update with actuals) @ 70 mph
  • 6th gear - 3,475
  • 7th gear - 2,900
  • 8th gear - 2,325
• Estimated (will update with actuals) @ 65 mph
  • 6th gear - 3,225
  • 7th gear - 2,700
  • 8th gear - 2,150 (I am expecting it can maintain speed considering the aggressive gearing makes it easier. If not, 66-67 mph should be no problem at all)

Data with 5.38 and 27 lbs alloy wheels:

• Average MPG - TBD
• Best MPG - TBD
• Worst MPG - TBD
• 0-60 - TBD

- Cheers

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[TheRealGinjaNinja]

Initial thoughts:
I just picked up the Jeep with the 5.38s and drove the first 20 miles break in at 60 mph, which included some steep grades going up 1,000ft elevation as well...I am stoked!

Drivability is much improved...no more sluggishness! As mentioned above I was a little worried about ~65 mph holding 8th on flat ground and to my surprise it was pulling in 8th with no effort at 60-62 up a small grade at ~2,000 rpms! Instant readout of mpgs are also much improved but too early to tell. Also...backing up into my driveway with a slight incline is also much easier!

I will work on getting the data updated in my first post after I get through the first 500 miles. Really exciting stuff, I should have done this much sooner!

Quick shoutout to the shop too...MULE Expedition Outfitters in Preston did a bang up job. They shared a pic of the gear patterning and it was absolutely perfect with minimal work to set up. Combination of great gear set (Dana Spicer) and installer.

-Cheers

 

[TheRealGinjaNinja]

Front gear pattern:

 

[ScottBeach]

Are you seeing any temp climb for the transmisson?

 

[TheRealGinjaNinja]

Are you seeing any temp climb for the transmisson?

Too soon to tell and I was not monitoring it. I will be sure to take a look thanks for calling it out.

 

[BuyHold]

I will work on getting the data updated in my first post after I get through the first 500 miles. Really exciting stuff, I should have done this much sooner!

This is awesome thread. Thank you for sharing and looking forward to the update, particularly about your assessment of the quality of the install after testing for a while. Are you getting a 500 mile or 1000 mile visual inspection? I understand that this is often, not always, part of gear package install process.

BTW: Are you in any way related to a Mojito JLU owning GinjaNinja?

 

[TheRealGinjaNinja]

This is awesome thread. Thank you for sharing and looking forward to the update, particularly about your assessment of the quality of the install after testing for a while. Are you getting a 500 mile or 1000 mile visual inspection? I understand that this is often, not always, part of gear package install process.

BTW: Are you in any way related to a Mojito JLU owning GinjaNinja?

Yep, I traded the Mojito JLUR in for my Gladiator with zero regrets! For whatever reason the forum doesn’t allow me to have the same name.

Regarding the gears - the crappy (tons of snow/ice) weather has been helpful keeping slower speeds during break in and keeping it in 4wd auto. I have about 430 miles on it and yes they do the 500 mile inspection as part of the installation. Gears are silent and the 5.38s are everything I wanted. Huge improvement across the board so far! Truck holds gears below 2000 rpm even up slight inclines. Had it up to 75 briefly after the first 100 miles and it was around 2550 rpm and comfortable.

I will provide a better update after the inspection and once I can get on it a bit harder. Love the gears and very impressed with the shop and their work.

cheers

 

[TheRealGinjaNinja]

Too soon to tell and I was not monitoring it. I will be sure to take a look thanks for calling it out.

So far after 430 miles I have not seen trans temps above 181*. Granted, it has been cold as hell lately.

cheers

 

[jeepers29]

So far after 430 miles I have not seen trans temps above 181*. Granted, it has been cold as hell lately.

cheers

What kind of mpg's are you getting with the new setup?

 

[BuyHold]

For whatever reason the forum doesn’t allow me to have the same name.

I have the same name on this Gladiator forum as on the JL forum. My guess as to why you were not able to get the same name is because @Ginjaninja beat you to it.

The O.G. Ginjaninja doesn't appear to be too active round here these parts.

 

[TheRealGinjaNinja]

What kind of mpg's are you getting with the new setup?

Trending positive…the attached pic shows my recent fill ups. My lifetime average is 13 mpg.

I only had one fill up since regearing. I admit it could be a bit skewed by slower overall speeds during break in but I also had a lot of idle time due to heavy snow/ice and extremely low overall temps which hurts it.

 

[jeepers29]

Trending positive…the attached pic shows my recent fill ups. My lifetime average is 13 mpg.

I only had one fill up since regearing. I admit it could be a bit skewed by slower overall speeds during break in but I also had a lot of idle time due to heavy snow/ice and extremely low overall temps which hurts it.

Thanks for the post. Glad to see it is moving in the right direction for you. Merry Christmas.

 

[JT1]

That's no too far from what I get. Mine is a 6spd with 5.13s and 37s. RPMs between 5.13s on the manual and 5.38s in the auto are similar. Full highway at 75 is about 14.5. At 65-70 I get about 17.

 

[Duece McCracken]

That's no too far from what I get. Mine is a 6spd with 5.13s and 37s. RPMs between 5.13s on the manual and 5.38s in the auto are similar. Full highway at 75 is about 14.5. At 65-70 I get about 17.

Are you happy with the 5.13?

 

[JT1]

Are you happy with the 5.13?

It is a night and day difference. The manual makes it worse.
4LO it was fine even on 3.73s, but there were times where starting in 1st pointing uphill on dirt in 4HI that it was either stall, slip the clutch alot or rooster tails.
5th gear was a downhill only thing. After the regear, once I hit 60-65 I can put it in 6th and set the cruise and never think about it again. Around town gas mileage went up about 10%. It's still a brick, so >75mph the mileage is bad, but at 65 I've seen 20 over a 2 hour trip.

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