5.13 or 4.88??? Please Help.

[JIMBO]

:sombrero: The 5.38 pinion is pretty close to the same size as the 4.10---in the HD D44 ie-8 teeth vs 10 teeth and my mileage has gone up to 18 mpg +++ after a 15 mpg average with the 4.10s-

I wonder what 5.38 would have been like with that trailer. Your RPMs at 70 would be still less than 2700. But that is moot, since, and I think, your front axle was a dana 30. I think 538 for D30 just came out. Talk about a tiny pinion gear:Wow1: I agree the 3.8 sucks, but that auto trans was complete ****.

I tach about 2600 rpm at 70 mph and although I'm still breaking in the 5.38s-the power increase is appreciable--

Course after breakin I won't be driving like a "Grandma" and the mileage will drop back down-

Wonderful update to the mild powered 3.8L-

:costumed-smiley-007:wings: JIMBO

 

[Ryanc]

That sounds like a perfect set up. My milage went up also. But I still drive like grandpa after the break in.

 

[wjeeper]

Just one thought about 4.88 vs 5.13 gears.......the pinion on a 5.13 gearset is starting to get awefully small and has less tooth contact with the ring gear.

(pinions are not out of the same axle, similar size, but different ratios) You can see what I mean.

 

[Rubicon_Fan]

Thanks Folks!!
Drove my friends Jk on 35's and 5.13s up the hwy and loved it. He had this set up for just about a year and had no issues. It drove fantastic, alsmot likes totally different vehicle. I was blown away, and that pretty much made up my mind to go 5.13s just because our highways are all in the mountains and that extra bit of tourqe is nice to have. I will take it easy and stay below 60mph to save some gas $$. Thanks you all!


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[RedRocker]

Now we can move on to synthetic vs dino oil.:sombrero:

 

[trail-explorer]

I'd recommend calling up David at Northridge 4x4 in Bremerton, WA and get his take on it. He has two JKs himself and has built quite a few.

Appreciate your opinions!
I have heard about JK's with double cardin driveshafts having vibration issues at hwy speeds. Most people say it has to do with pinion and caster angles. To avoid these vibes it is recommended to stay below +4* caster. Now, from what I understood 4.88 will bring me back to stock, which is great, but I also want to mention that I'm In BC and most of our hwys are very hilly.
I like the idea of 4.88 and lower rpms, but would I regret not going 5.13 going up the Coquihalla (very steep hwy)???


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[Rubicon_Fan]

I'd recommend calling up David at Northridge 4x4 in Bremerton, WA and get his take on it. He has two JKs himself and has built quite a few.

Thanks, I bought all my parts from Dave! Awesome guy indeed!! I had him in mind, and was even thinking driving down to his shop and get everything done through him!

 

[mmccurdy]

I have 5.13's and 35's and I'm pretty happy with the setup, even while towing. I have the manual trans and I find that I have to drop into 5th or 4th on long, hard climbs. I like to keep my revs under ~3.5k, not because I have vibration issues, but just to avoid wear and tear on the engine and driveline.

I'm also happy with this setup off road, though the reduced pinion size (esp. on my D30 front) does worry me a little bit. Regardless, you know how I wheel and I've been fine to date.

I've done several long trips with some comparable rigs, and I have some real-world findings in terms of economy. My buddy running with an auto trans, same 5.13 gears, same 35" tires (but him with a superchip to help and me with a gobi rack to hurt) he did about 1.5 MPG better than I did. We've also run with a two door, same gears, same tires, no rack, no Superchip, who was pretty much matching me perfectly. Needless to say I'm thinking of picking up a Superchip, but just to show you that 1-2 MPG can be from lots of other factors besides gear ratio.

Eddie and the guys running 40's have to stop for gas when I'm showing 1/4 to 1/3 of a tank, but of course they're pushing 40's, 5.38's, and D60's (a *lot* more weight in the drivetrain). Same goes for the Hemi guys -- they've been the limiting factor in any caravan I've been with so far. I would have close to half a tank when they were calling for gas stops.

At the end of the day I really think the difference between 4.88's and 5.13's is going to be pretty minor from the driver's seat and also from an MPG standpoint, so if the deeper gearing makes you happy, go for it.... I don't have any regrets in that department. If I wanted to nickel and dime on fuel economy, I wouldn't be driving a brick down the road at 80MPH (130 KMH)

:smiley_drive:

 

[toymaster]

Thanks Folks!!
Drove my friends Jk on 35's and 5.13s up the hwy and loved it. He had this set up for just about a year and had no issues. It drove fantastic, alsmot likes totally different vehicle. I was blown away, and that pretty much made up my mind to go 5.13s just because our highways are all in the mountains and that extra bit of tourqe is nice to have. I will take it easy and stay below 60mph to save some gas $$. Thanks you all!

:victory::victory::victory: Keep it at 60-65 and 70s going down hill...you'll be happy all the way around....