My current rig has DANA30 front, DANA44 rear, 3.73 ratio, limited rear slip differential, stock 30 inch tire. Nothing exciting and pure stock performance.

I am planning to upgrade it to fit in 35 inch tire. To me, all upgrade should
start from a healthy internal meachnism.

Therefore, I think before resizing the tire, a upgrade in the gear ratio
is needed so that the effective gear ratio will be near stock for on street
driving and really low for good trail performance.

Now I am facing two choices, upgrade axle gear ratio or upgrade transfer case.
My research so far so showed the pro/cons on each choice as

Axle Gear Ratio Upgrade:
Pro: Parts price is affordable, 400 dollars can get both front and rear
pinion/ring pairs.

A lot of ratios can be selected ranging from 4.1 to 5.38.

Can be done with locker upgrade at the same time.

Con:
Expensive labor.

DIY is hard, not only because you have to deal with a lot of stuff
before reaching the pinion and ring part, but also the adjustment of
backlash and preload is quite tricky and time consuming.

have to do it on both front and rear axle

When upgrading the gear ratio, if we do not upgrade axle
(from DANA30 to DAN44 or from DANA44 to DAN60)
it will make the axle weaker.
This is because lower gear ratio require smaller
pinion size or larger number of ring gear teeth, making
contact area between pinion teeth and ring teeth smaller than
stock size.


Transfre Case Upgrade:
Pro: Just need to change one part (transfer case) then two (two axles)

Atlas-4speed unit provide a wide choices of gear ratio. Compared
to it, stock transfer case provide only two choices, the one for street
use is too low and one for trail is too high.

keep the stock axle strenght without weakening it

Cons: Expensive Part, expensive labor

Do not know if it is suitable for DIY, since it seems like a
really big change and you have to at least cut center console
to let the new stick of the transfer case to through


All above is my current research result and there maybe some erros.
corrections/comments/suggestions?

 

The axle ratio and locker changes will be by far the better upgrade compared to the transfer case. It's my opinion that the difference between the two transfer cases would be splitting hairs anyway. I cannot imagine where two equally prepared Jeeps except for transfer cases would be different in regards to where they could go. The gear braking with the Rubi case is certainly a nice feature, but not worth sacrificing the upgrade from axle gears and lockers.

 

Thanks RedneckJeep:

Are you talking about Rubicon's transfer case that offer 4.1 ratio?
Then I agree it is not quite different from X/Sahara's transfer case that offer 2.72 ratio.


But I am talking about Atlas 4Speed transfer case that can offer up to 10.0
ratio.

To me, keeping the stock 3.73 gear axle ratio plus this new Atlas transfer case,
it gives good on street MPG (due to the stock 3.73 stock axle ratio) and great
offroad performance (maximum 10.0 transfer case ratio or selected 2.0, 6.0 transfer case ratio).

The reason that I am more for transfer case swap is because gear ratio
upgrade (without upgrade axle itself) is weakening the axle due to smaller
teeth of pinion/ring gear.

By the way, I agee with you about locker change too.

I believe adding a locker to the current differential or upgrade differential with a locker differential is easier than upgrading gear ratio. Am I correct or wrong on this?

 

I gotta agree with RNJ on this one.

Take it from someone who has gone the path before you (me); gears before any thoughts of a t-case. The JK is a different animal once in its powerband. I'm not saying it's a fire-breathing dragon, but the V6 has plenty of usable power and torque for my 33s being turned with 4.88s (and I could probably get away with 35s if I wanted them).

 

Thanks Omaha:

But can you give me technical reasons why gear ratio upgrade is better
than transfer case upgrade?

To me, it is the final gear ratio that counts, i.e
trasnmission gear ratio x transfer case gear ratio x axle gear ratio

So, upgrade transfer case ratio has the same effect as axle ratio, is it
correct?

 

go with gears. thats my next step. i'm running 35's right now. it's not to bad. but you can feel the change going from stock tires to a 35. so 5.13's are in my future.

 

Yes, adding a locker without a gear change is less challenging. Since the pinion gear does not need to be removed, you are basically leaving gear settings alone. Except of course for ring gear backlash, which is relatively easy to get back into spec. All you need to do is simply replace any spacers in the order and side from where they came.

I've actually had no experience with the Atlas unit.....however, I have had extensive experience with gear changes and 4X4 drivetrains. It's "MY" personal experience that not much will compensate for better final drive gearing. I may be totally off base, but I think I am right on this.

Take the transfer case out of the equation for a minute. What do you have? An underpowered, incorrectly geared Jeep from the factory. These things make their best power starting around 2500 and going UP. They needed more final drive gear to begin with. You can throw the best transfer case at it in the world, and you're still under geared on the road. Why not do both? Then you'll have the best of both worlds.

Somebody feel free to correct me if I'm wrong on any of these points.

 

You can not make these two options a choice, rather a priority.

They are two different animals with two different uses. As far as weakening the axle, forget about that. The JK ring and pinion is very thick even in the lower ratios and very strong.

Think about the ring and pinion change necessary for drivability on the street, and the Transfer case for drivability on the trail, and on low range only. You can change transfer cases all you want and never notice it on the street. You can change ring and pinion all you want and barely notice it on the trail in low range.

With your gears, I would recomend going with the ring and pinion change first, and yes install lockers at the same time. You will not break the ring and pinion, and if you start breaking this, you are driving the wrong vehicle anyway. This will get you excellent drivability on the road, and the lockers are awesome to wheel with, even with the stock transfer case.

Once you take it on the trail, the stock transfer case is not bad, unless you do some serious rock crawling, and a 6 speed makes it worse. As my wheeling has progressed to more seriouos stuff over time, I am now wanting a lower crawl ratio. You will know, based on the wheeling you do, if you then need to look at changing your transfer case gearing. The lower ring and pinion will help on the trail, but in low range, not much.

 

What you refer to here is not the final drive ratio. Final drive ratio is that of the axles only. Effective ratio is what you are referring to when you factor in transfer cases and overdrives. In the end, the final drive ratio is unchanged.

 

Remember that a transfer case, regardless of the crawl ratio, is still 1:1 on the street in 2 hi or even 4 hi on the trail. Only low range changes.