Explain Transfer Case to me?

Hey all. I had some questions about TC and was looking to gain some knowledge.
I have a basic understanding about them...that they convert power from the engine to drive shafts and that turns the axles then the wheels, but that's about it.
I notice that this is a desirable upgrade to go from a Sport to a Rubi or even an Atlas but don't understand the benefits of this.
Can someone explain in layman's terms yet detailed how these work and the benefits of swapping them?

Gearing inside them. The stock low range on the sport is roughly 2 to 1 where as the rubicon case is 4 to 1 so it's lower geared and better for rock crawling. The atlas cases can be ordered with several different ranges of gears.

Thanks for the response. So let's say you change axle gearing to a lower gear...like 4.88...this allows for a lower range 1st gear then stock...correct?
With a 4 to 1 Rubi TC...how does that effect your crawling? Does it allow for a slower 1st gear or something? More torque?

You have to look at overall gear ratio which is the combination of selected transmission gear, transfer case gear ratio, differential ratio and tire diameter. Usually people go to a higher differential reduction (say from 3.21 to 4.88 ) to make up for putting larger tires on which keeps the two 'in synch'. The higher total number the higher RPM for a given speed and more torque applied at the point of ground contact, and slower vehicle speed for a given engine speed - great for rocks.

It gives you more engine speed but at a slower vehicle speed. So it gets the motor into the torque at a slower vehicle speed. The higher the number the lower the gears and the higher the RPMs you will get out of your engine.

In the 4x4 world the higher the number in axle gears the bigger the tires you can run and will want to run since your RPMs will also go up. The bigger tires will help bring them back down. In other words, you don't want to run a 5.13 gear and a 33 inch tall tire. You would be better on a 37 with 5.13s.

However with a sport model with a Dana 30 the pinon gear on a 5.13 is incredibly small so you would be best to not run a 5.13. A 4.88 would be the smallest you would really want to go. Idk what the 3.6 with a 6 speed and 35s is like as I have an auto but have 35s and 4.10s and I feel that it's a great combo. I also have a rubicon so I have the 4.1 low range so offroad it should be good too. Once I go to 37s I'll be looking at 5.13s. With the 6speed you should be ok with 4.88s and 37s I believe. On 35s I think it would be great with 4.10s. However it's practically not worth swapping to 4.10s money wise unless you were pretty sure you would stay on 35s.

Maybe somebody with more experience with the 3.6, 6 speed, 35 combo can chime in.

I think its important to remember that in high range there is no gear reduction in the transfer case. It is 1 to 1. No different than running out of the transmission directly into the differential in a 2 wd. The job of the transfer case is to redirect power to the front axle.

Along the way someone decided that it was a great location to add gear reduction for offroad purposes.

The sport jk's have a 2.72 to 1 gear reduction, while rubicons are 4 to 1. The 4 to 1 will drastically change your crawl ratio. Crawl ratio is calculated by using your transmission gear ratio, transfer case ratio, and differential ratio. Tire size will impact your speed in feet per minute, but will not change your crawl ratio. The higher the number the slower you travel. As stated above, low crawl ratio's are good in the rocks, but there are disadvantages to gearing excessively low.

I have a 3.6 with 35's and 4.10 gears on a 6 speed. It does okay. I think 4.56 would be the best setup for all purpose driving. Mine is a daily driver. I'm planning on going to 37's with 4.88, so i can handle the slight loss of power. 1st gear with stock tires and 4.10 traveled about 40 feet before a shift was required. 1st is what I'd call closer to normal right now.

My disclaimer. This info is as I understand it. Feel free to correct me if it is off a bit.

This kid does a really good job of explaining the internal workings. He also has related videos.

https://www.youtube.com/watch?v=K1qj8dHTmP4

Thanks for all the responses guys. I think I have a better understanding of it. My primary issue is that running stock gears on an Unlimited Sport...I tend to stall a lot in 4Lo in 1st gear and have to give more gas than I would like while feathering the clutch to keep speed down...thus preventing breaks.
I was hoping changing axle gears would help as I haven't done that yet, but just wondering if a TC is the best solution for my dilemma.
I would hate to replace the clutch because of my driving when a TC is the solution.

If you have stock gears and 35s I would definitely look at changing them. You also wouldn't be hurt to change the transfer case to either a rubi take out or an atlas but I would do gears first as that would help other things than just the stalling while crawling.

UpsideUp said:

Thanks for all the responses guys. I think I have a better understanding of it. My primary issue is that running stock gears on an Unlimited Sport...I tend to stall a lot in 4Lo in 1st gear and have to give more gas than I would like while feathering the clutch to keep speed down...thus preventing breaks.
I was hoping changing axle gears would help as I haven't done that yet, but just wondering if a TC is the best solution for my dilemma.
I would hate to replace the clutch because of my driving when a TC is the solution.

Click to expand...

I have a sport with 513s and yes it will help to do just gears for now (I can put it in 4lo take foot of clutch and it will walk on its own). Still isn't as good as the rubi 4:1 but gears will help.

Yes I run a D30 still with 513s and 35s but I am willing to take the risk.

For your situation I would do the axle gears first, as this will, 1) increase performance everywhere, 2) reduce clutch slip needed for slow speed driving off road, 3) help your engine and tranny last longer due to reduced stress. If you still want a lower crawl ratio, look to purchase a used Jeep Rubicon transfer case, as it will have the 4:1 gearing. Plus you can find them for about $1,000. The Atlas is going to cost you 3K by the time you are done,,, if not more. Good luck!

With the Rubi you can actually start the Jeep while in 4-low in first without the clutch, I don't think you can do that with the other transfer case. I don't think I've ever slipped the clutch in the rocks, only used it for shifting as sometimes reeaallll slooooow is too slow.

Best bet is to ride with someone who has the 4:1 to see the difference, in the rocks it is king (if you ignore the Atlas option).