5.38 gears
Thread Starter
JK Enthusiast
Joined: Apr 2009
Posts: 146
Likes: 0
From: Bryan, OH
5.38 gears
i just got my jeep back today after getting a d44 up front and 5.38 gears front and back. i took it around the block real quick and it seemed to have a bit more pep than before, but my question is where is the difference most noticeable?
people talk about gearing being the best bang for your buck you can get. it just wasn't quite as big of a change as i had expected. i'm at work and i can't take it up to 70 mph like i want, so i'm wondering what other people have experienced with gearing changes that makes it so awesome. i mean my bill is gonna be like 3400 bucks here so i'm hoping i didn't waste too much cash
people talk about gearing being the best bang for your buck you can get. it just wasn't quite as big of a change as i had expected. i'm at work and i can't take it up to 70 mph like i want, so i'm wondering what other people have experienced with gearing changes that makes it so awesome. i mean my bill is gonna be like 3400 bucks here so i'm hoping i didn't waste too much cash
JK Enthusiast
Joined: Jul 2008
Posts: 204
Likes: 0
From: Aurora, CO
I just pulled the trigger on 5.38's today
My Auto/4 door/ 4.88 combo was OK for the Colorado Passes, but sucked on flat highway. The tranny could never decide between OD and 3rd
The RPM chart listed above with Auto/ Manual is the key while planning for future mods.
(Paying big $$$ for the same parts twice sucks)
My Auto/4 door/ 4.88 combo was OK for the Colorado Passes, but sucked on flat highway. The tranny could never decide between OD and 3rd
The RPM chart listed above with Auto/ Manual is the key while planning for future mods.
(Paying big $$$ for the same parts twice sucks)
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
with the 3.8L V6 JK engine.
JK Super Freak
Joined: Aug 2009
Posts: 1,255
Likes: 2
From: GRANDE PRAIRIE, AB
Not sure where you got that idea--unless you are looking at the generalized charts that do no match our engine torque/horsepower curve and transmission gearing.
With an automatic and 35s with 5.38s, your rpms are 2495 at 70 mph.
That is perfect for a highway rig with the 3.8L V6 JK engine. Your gas mileage would likely be around 18 at that rpm and your rear wheel horsepower at that rpm should be enough to avoid downshifting on hills and in windy situations.
With a 6 speed and 35s with 5.38s, your rpms would be 3038. That would be a little high. Your gas mileage would probably drop to 14 mpg.
Here is a correct chart:
With an automatic and 35s with 5.38s, your rpms are 2495 at 70 mph.
That is perfect for a highway rig with the 3.8L V6 JK engine. Your gas mileage would likely be around 18 at that rpm and your rear wheel horsepower at that rpm should be enough to avoid downshifting on hills and in windy situations.
With a 6 speed and 35s with 5.38s, your rpms would be 3038. That would be a little high. Your gas mileage would probably drop to 14 mpg.
Here is a correct chart:
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JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
can't see the chart but is the over drive that much different from auto to manual?
42RLE—Automatic, Four-Speed Overdrive
Gear Ratios 1st 2.84
Gear Ratios 2nd 1.57
Gear Ratios 3rd 1.0
Gear Ratios 4th 0.69
Gear Ratios Reverse 2.21
Axle Ratio 4.10
Overall Top Gear 2.83
NSG 370—Manual, Six-Speed Overdrive
Gear Ratios 1st 4.46
Gear Ratios 2nd 2.61
Gear Ratios 3rd 1.72
Gear Ratios 4th 1.25
Gear Ratios 5th 1.00
Gear Ratios 6th 0.84
Gear Ratios Reverse 4.06
Axle Ratio 3.21 Std., 4.10 Opt. (Std. on Rubicon)
Overall Top Gear 2.69 Std., 3.44 Opt. (Std. on Rubicon)
JK Enthusiast
Joined: Dec 2008
Posts: 163
Likes: 0
From: Idaho Falls, ID
I have ran 4:88s and now have 5:38s and wouldn't even dream of going back! With 4:88s I couldn't hold overdrive with any wind at all. We just have to realize the 3.8 is under powered for the application. This vehicle should have had a small v8 from the factory.
JK Junkie
Joined: Jul 2009
Posts: 2,343
Likes: 1
From: The San Andreas Fault
i just got my jeep back today after getting a d44 up front and 5.38 gears front and back. i took it around the block real quick and it seemed to have a bit more pep than before, but my question is where is the difference most noticeable?
people talk about gearing being the best bang for your buck you can get. it just wasn't quite as big of a change as i had expected. i'm at work and i can't take it up to 70 mph like i want, so i'm wondering what other people have experienced with gearing changes that makes it so awesome. i mean my bill is gonna be like 3400 bucks here so i'm hoping i didn't waste too much cash
people talk about gearing being the best bang for your buck you can get. it just wasn't quite as big of a change as i had expected. i'm at work and i can't take it up to 70 mph like i want, so i'm wondering what other people have experienced with gearing changes that makes it so awesome. i mean my bill is gonna be like 3400 bucks here so i'm hoping i didn't waste too much cash
With the 3.73s I was not comfortable pulling out into the fast lane on a grade, but the 5.13s its not a problem unless the JK is heavily loaded.
I chose the 5.13s because I didn't want my RPMs to fly above 3500 if I dropped out of overdrive while driving 75-80 MPH (which I would obviouslly never do ) . But besides that, I could definitely use the additional RPMs provided by the 5.38s in the city and offroad.
I certainly support the statement that "gearing is the best bang for the buck". Maybe you just need the gears and the new axle to break in.