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Atlas JL Transfer Case

Jeep’n Jay

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grimmjeeper

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I had an 11.7 4 speed atlas behind the manual transmission in my JK. I almost never used the 11.7 low range. I mostly drove around in 4.3 low range. At idle in first gear and compound low, it took 20 second or so for the tire to make a full rotation. That's with 4.56 gears and 315/70R17 tires.

Honestly, if I was going to build another rock crawling JK, I'd stick with the 4.3 Atlas or a Rubicon with the 4.0 case. And as I build up my Comanche, I'm doingan ORD Magnum box with an NP205 giving me 1:1/1.96:1/2.72:1/5.33:1. Behind an automatic with the right axle gears for the tires, I doubt I'll need more than that, even in Moab or Sand Hollow.

One other thing to consider. The 4 speed atlas was not available for the JK with the automatic because the computer couldn't work with a multi speed transfer case and still shift the transmission correctly. The transmission doesn't have a tailshaft speed sensor so the computer relies on the wheel speed sensors and knowing a single low range ratio.

I don't know if the 8 speed in the JL will work with the 4 speed atlas or not. But it's something to look into.
 

word302

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My dear friends, the wishes of both of us are not the same
You are looking to travel the trails
I'm looking to crawl and climb rocks
Therefore transfer ratios in rocks are completely different from travel on trails.
See an example of what is available today for JK.


Ratio's of the Atlas 4Speed are:

1.5:1, 2.72:1, & 4.08:1 Recommended for all applications

2.0:1, 2.72:1 & 5.44:1 Recommended for all applications

2.72, 3.0:1 & 8.16:1 Recommended for all applications

2.72:1, 3.8:1 & 10.34:1 with this low gear ratio, high horsepower engines are not recommended

2.72:1, 4.3:1 & 11.70:1 with this low gear ratio, high horsepower engines are not recommended
Have you ever driven anything with a 10:1 low range? Even with the manual that would be silly. With the automatic it wouldn’t even be useful. Yes I rock crawl. 4:1 is perfect for the manual, borderline too low for the automatic.
 

grimmjeeper

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Have you ever driven anything with a 10:1 low range? Even with the manual that would be silly. With the automatic it wouldn’t even be useful. Yes I rock crawl. 4:1 is perfect for the manual, borderline too low for the automatic.
There were several obstacles where the 4 speed atlas in my JK in compound low was an advantage. Having an engine like the 3.6 with a manual was frustrating because of the lack of low end torque. The super low case let me do very slow technical crawling with an engine and transmission combo not suited to that kind of driving. While I didn't use it a lot, I did use it and wasn't sorry I had the option.

With an automatic that has a higher stall torque converter lets you get the RPMs up where you need them to crawl. So I wouldn't put one behind an automatic. Not that deep. But that's just my own use case.

Just because you don't feel a need for it doesn't mean it's not useful to other people.
 
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word302

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There were several obstacles where the 4 speed atlas in my JK in compound low was an advantage. Having an engine like the 3.6 with a manual was frustrating because of the lack of low end torque. The super low case let me do very slow technical crawling with an engine and transmission combo not suited to that kind of driving. While I didn't use it a lot, I did use it and wasn't sorry I had the option.

With an automatic that has a higher stall torque converter lets you get the RPMs up where you need them to crawl. So I wouldn't put one behind an automatic. Not that deep. But that's just my own use case.

Just because you don't feel a need for it doesn't mean it's not useful to other people.
I get it, but 1st gear on the JL is significantly lower than the JK manual was. There comes a point when your crawl ratio just gets silly. With the 4:1 transfer case and 5.13 gears I'm well above 100:1. Even with stock gearing you'd be looking at a crawl ratio of well over 200 with a 10:1 case. I still argue that 4.3 or even 5 would be the sweet spot.
 

grimmjeeper

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I get it, but 1st gear on the JL is significantly lower than the JK manual was. There comes a point when your crawl ratio just gets silly. With the 4:1 transfer case and 5.13 gears I'm well above 100:1. Even with stock gearing you'd be looking at a crawl ratio of well over 200 with a 10:1 case. I still argue that 4.3 or even 5 would be the sweet spot.
Mine was just a hair under 238:1. And I used that from time to time doing technical rock crawling. Not all the time. Sometimes I was in compound low in 3rd or 4th gear. But being over 100:1 does have it's advantages.

Again, just because you don't use it doesn't mean it's not useful to someone else.
 
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word302

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Mine was just a hair under 238:1. And I used that from time to time doing technical rock crawling. Not all the time. Sometimes I was in compound low in 3rd or 4th gear. But being over 100:1 does have it's advantages.

Again, just because you don't use it doesn't mean it's not useful to someone else.
Which is why I asked if he had any experience with a 10:1 case.
 

J0E

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There were several obstacles where the 4 speed atlas in my JK in compound low was an advantage. Having an engine like the 3.6 with a manual was frustrating because of the lack of low end torque. The super low case let me do very slow technical crawling with an engine and transmission combo not suited to that kind of driving.
Automatic's have a huge advantage over manual, but even so 10:1 is way beyond silly. Invest in an auto, not a silly gear. See https://bt39.com/GearWheelSpeed and edit the JLR-6sp transfer case to 10:1

JLR-6sp31.5 : 105.132.631.5310.810.72-4.49
SpeedHi Range9.117.830.646.957.865.1-10.4
SpeedLO: 42.34.57.711.714.516.3-2.6

At 5,000 RPM you're going 2.3 MPH. Top speed of 16 MPH is silly.

My JLR auto rock crawls mostly in 2nd gear and I've never stalled it, lol.
 

grimmjeeper

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Automatic's have a huge advantage over manual, but even so 10:1 is way beyond silly. Invest in an auto, not a silly gear. See https://bt39.com/GearWheelSpeed and edit the JLR-6sp transfer case to 10:1

JLR-6sp31.5 : 105.132.631.5310.810.72-4.49
SpeedHi Range9.117.830.646.957.865.1-10.4
SpeedLO: 42.34.57.711.714.516.3-2.6

At 5,000 RPM you're going 2.3 MPH. Top speed of 16 MPH is silly.

My JLR auto rock crawls mostly in 2nd gear and I've never stalled it, lol.
tl;dr at the end

Yeah, I may know a thing or two about gear ratio calculations... ;)

The torque converter really makes a huge difference. Properly matched to the engine, it lets you get the RPMs in their optimal range and it acts as a buffer that gives you the control you need to crawl.

I will say that if you have one of the older automatics without overdrive like the Powerglide, TH350, TH400, C4, C6, TF904, TF727, etc. you end up having to deal with a very narrow range of available gears. A multiple speed transfer case would be appropriate there. You can gear your axles with highway friendly gears and still be able to get towards a useful crawl ratio. For example, a TH350 has a first gear of 2.48:1 and top gear of 1:1. Put in 3.07 axle gears for highway cruising and add a 10:1 low crawl ratio you're still only at 76:1 in first gear low range.

Of course, our JLs have an automatic with a spread 3 times as wide as the TH350 (and the rest of them). First gear is basically 2x the first gear on the TH350 and you get overdrive at the other end. Going from 5:1 to a tall overdrive gives you so much more. So a really deep transfer case is redundant and actually goes well beyond what you'd really need for crawling.

So when it comes to transfer cases in the JL with the factory automatic, I agree that a 4 speed Atlas is a whole lot of overkill.


However, when it comes to the Pentastar and the manual transmission, things are different. The Pentastar really lacks off idle torque. When I had my JK with the manual and 4.56 gears with the 2.72:1 sport transfer case, I found I couldn't crawl. I would either stall it or bounce badly because I had to gun it. A 4:1 Rubicon transfer case (along with the 4.88 gears I should have gotten) by itself would have made a big difference. The 4.3:1 in the Atlas I installed really had an impact. But I still ended up in a few situation where I wanted more. Fortunately, it was a 4 speed Atlas and it was easy to just shift the 2:72 range box in and get a silly low crawl ratio that ended up actually being useful. A lot of the time, I'd start off in 2nd or 3rd gear because 238:1 really is too much. But 2nd gear was 139:1 and that's a pretty good crawl ratio for a Pentastar turning 35's with a clutch.



tl;dr: A 4 speed Atlas is a waste behind the factory automatic in a JL. But still useful behind the manual.
 

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I don't see the waste of the 4sp TC on the JL automatic, I like to go dunes and also rocks, which for example on the dunes, low is too low, and high needs a little bit more power.

On rocks it is flawless, so going to a 4sp with a 1:1, 2.72:1, and 4:1 would be a great sweet spot for many stuff.

It really depends on the needs of each person.
 
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Some Random Guy

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Just to be sure I understand their site, these are not available yet? I’m debating ordering a Rubicon T-case this summer so I can install it in spring along with full floats (and subsequent parts).
 

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Have you ever driven anything with a 10:1 low range?
I am on 37s and stock gears so far and 4:1 is too low for some stuff. Cannot imagine 10:1...I'll get my gears first.

Now, a standard low range and a 5:1 for hairier stuff...I could get on board with that.
 

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