Why the 392 doesn't need Rubicon transfer case?

[Deen]

My guess is that the reason for not having the 4:1 case is that the torque output of the 392 + 4:1 case would exceed the limits of the front and rear (D44) axles.

The 392 is rated at 470 ft lbs, the diesel is 460 ft lbs but at much lower rpm.
I also am tired of having to shift in and out of 4L.
You want to crawl? Try 4.88 gears in the diesel. I did, and found I was using 4H for almost everything even at Moab.
So far I've tried 3.73, 4.88 and now 4.10. 37's and 4.10's are good but wish I had gone with 4.56 this last change.

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[2020 Rubi Diesel]

Maybe if deleted.

JLURD with the Bank derringer/pedalmonster on 40s and get 19-22mpg on the interstate cruising 70-80mph. Around town is like 15mpg. When my 16 yr old son drives it I get 0mpg as he doesn't know how to fill it up....

 

[swampflyer]

My guess is that the reason for not having the 4:1 case is that the torque output of the 392 + 4:1 case would exceed the limits of the front and rear (D44) axles.

Or the driver

My guess is that the reason for not having the 4:1 case is that the torque output of the 392 + 4:1 case would exceed the limits of the front and rear (D44) axles.

Or the driver.

 

[Sidewalk]

I could have swore I remember one of the guys I wheel with say he doesn't even use 4 low. I can't remember what he was running, but definitely a minimum of 37's with the V6.

My old Bronco II didn't have problems with tall gearing because of the automatic transmission. I needed to regear it, but I was too broke back then. Did fine with 140 HP.

Ohh My Gawd ! He has to shift the TC ! Ohh, the agony ! … Jeeez
my 63 had 16 forward speeds, and 4 reverse, with 4 sticks, it wasn’t difficult. Now he has an 8 spd automatic transmission and a 2 speed TC he actually has to shift for the same 16 speeds and complains …. remarkable.

It is pretty hilarious to read about someone having to actually shift at all.

Guess Jeep needs to add a push button tcase for the next 392 to go along with the push button transmission

 

[jellis4148]

I guess I'm different. I'm considering an atlas t-case in the future with 5 to 1 gears for 4LO. I want the Jeep to go up the steepest incline in first gear with no gas pedal needed.

 

[Zandcwhite]

Hey I said crazy in a positive way. I mean look at this, and he said he still gets over 20 mpg Diesels are crazy impressive. I doubt the Pentastar would even move with all that.

The pentastar moves the JLUR on 39s no problem even with the stock 4.56 gears. Of course it moves the JT with 37s and 4.10s pulling an 8400 pound trailer so why would a little bigger tire be a deal breaker. Could it use more power? Absolutely. Will the thing still hit 100mph in the desert no problem? Of course.

 

[TEAMSLO]

392 with Atlas 3.8:1 and put it in neutral with brake applied when not moving in 4lo as it takes a significant amount of brake pressure to keep it from moving. I was lucky that the shop recommended against the 4.3:1 that I was originally wanting, would have been a big mistake.

Good side is absolute control with left foot breaking, feels the way it should when on obstacles. The slight down side is while in between obstacles, you're pretty much limited to 12-15mph, but there bigger fish to fry.

This forum is tough with people asking questions and such lol.

 

[Snacktime]

Probably due to the better overall offroad experience. 4:1 case is more critical if you have a manual transmission. The 8 speed has enough ratio that 4:1 is a limiting factor in some environments.

On an automatic the torque converter plays a much bigger roll which no one ever really talks about. You can drastically change how your vehicle performs in similar ways to a transfer case ratio change.

 

[roaniecowpony]

392 with Atlas 3.8:1 and put it in neutral with brake applied when not moving in 4lo as it takes a significant amount of brake pressure to keep it from moving. I was lucky that the shop recommended against the 4.3:1 that I was originally wanting, would have been a big mistake.

Good side is absolute control with left foot breaking, feels the way it should when on obstacles. The slight down side is while in between obstacles, you're pretty much limited to 12-15mph, but there bigger fish to fry.

This forum is tough with people asking questions and such lol.

A higher stall torque converter could make that a non-issue. I spoke with the Motech guys about an LT swap and this issue came up.

 

[Jeep Junkie]

It was my first time on that trail to the lake, and this 392 guy said follow me, and he was going over obstacles like crazy and on that silent remote trail his exhaust sound was all over the place. I had a tough time keeping up with him

 

[Jeep Junkie]

If this 392 guy is on this forum, listen dude, please wash your engine bay

 

[calemasters]

Wait, what? The EcoDiesel + 4:1 transfer case combo is pretty damn awesome on the rocks. What does he hate about it?

I agree. With my JLURD I am traction limited, never torque limited. With 442 lb.-ft. of engine torque going into the ZF 8 speed, TorqueFlite 8HP75 with a 4.71 1st gear ratio plus torque multiplication from the torque converter, then the 4:1 transfer case and then 3.73 differentials, this gives a 70.27 crankshaft to axle rpm ratio. I am surprised the wheels don't spin inside the tires.

 

[Riverjeep]

I know the Hemi produces a ton of torque but Rubicon transfer case also gives you a slower 4Lo. What about that, 392 owners don't miss that? In my case, the Willys transfer case does just fine but I wish my 4Lo and 1st gear was super slow like the Rubicon. I can use Jeep's hill descent feature or whatever it is called but I love engine braking.
Or Jeep sees 392 as a high speed offroader? I thought Mohave was the desert runner.

Sorry to be the AI guy but honestly they do give some pretty good answers.

The Jeep Rubicon 392 doesn't use the more aggressive 4:1 low-range transfer case found in other Rubicons because its powerful 6.4L HEMI V8 produces so much torque that a lower ratio isn't needed for extreme crawling, and Jeep chose a more durable, full-time (AWD-capable) clutch-based transfer case (MP3022) with a milder 2.72:1 ratio for daily drivability, though some enthusiasts find its clutch pack weaker for hard off-roading than traditional setups.


Why Jeep Chose This Setup:

• Abundant Torque: The 392 engine's massive low-end grunt means it has plenty of power to overcome obstacles even with the standard 2.72:1 low range, making the 4:1 ratio redundant for its intended use.
• Full-Time 4WD: The 392 uses a Selec-Trac system with an "Auto" mode, allowing it to function like an All-Wheel Drive (AWD) vehicle on pavement, sending power to all four wheels as needed, which is great for all-weather driving.
• Simplicity & Durability (Intended): This system (MP3022) is designed for seamless on-road use and is a proven unit, though its clutch pack can be a point of failure under extreme stress, notes DrivingLine, DrivingLine.

What It Means for Off-Roading:

• Milder Low Range: The 2.72:1 ratio is less aggressive than the 4:1 in regular Rubicons, requiring slightly more wheel speed or revs to crawl slowly.
• Clutch-Based System: The inherent clutch in the transfer case can wear out with hard off-road use, leading some owners to upgrade to stronger, gear-driven transfer cases like the Advance Adapters Atlas for serious trail performance, say Advance Adapters and Advance Adapters users.

 

[Zandcwhite]

Sorry to be the AI guy but honestly they do give some pretty good answers.

The Jeep Rubicon 392 doesn't use the more aggressive 4:1 low-range transfer case found in other Rubicons because its powerful 6.4L HEMI V8 produces so much torque that a lower ratio isn't needed for extreme crawling, and Jeep chose a more durable, full-time (AWD-capable) clutch-based transfer case (MP3022) with a milder 2.72:1 ratio for daily drivability, though some enthusiasts find its clutch pack weaker for hard off-roading than traditional setups.


Why Jeep Chose This Setup:

• Abundant Torque: The 392 engine's massive low-end grunt means it has plenty of power to overcome obstacles even with the standard 2.72:1 low range, making the 4:1 ratio redundant for its intended use.
• Full-Time 4WD: The 392 uses a Selec-Trac system with an "Auto" mode, allowing it to function like an All-Wheel Drive (AWD) vehicle on pavement, sending power to all four wheels as needed, which is great for all-weather driving.
• Simplicity & Durability (Intended): This system (MP3022) is designed for seamless on-road use and is a proven unit, though its clutch pack can be a point of failure under extreme stress, notes DrivingLine, DrivingLine.

What It Means for Off-Roading:

• Milder Low Range: The 2.72:1 ratio is less aggressive than the 4:1 in regular Rubicons, requiring slightly more wheel speed or revs to crawl slowly.
• Clutch-Based System: The inherent clutch in the transfer case can wear out with hard off-road use, leading some owners to upgrade to stronger, gear-driven transfer cases like the Advance Adapters Atlas for serious trail performance, say Advance Adapters and Advance Adapters users.

And this is why AI is damn near useless. The AWD transfer case is the weakest factory case available. The clutches fail, especially wheeled hard behind the 392. I agree the 392 doesn't need the 4-1 because of is torque output, but it would be more durable with the standard part time transfer case.

 

[zouch]

i also have the EcoD with 37s and 4.56s, and specifically did not want the 4:1 t'case of the Rubicon. (it's one of several reasons i ordered a Willys instead of a Rubicon on which to do my build.)

even with the powerplant in stock trim, with the automatic ZF and it's torque convertor, the abundant low-RPM torque of the diesel does a pretty fine job in the rocks, and with the 2:7.2 t'case i'm not wound out if running 4Lo between sections.

That's bizarre. Maybe he is trying to use 4lo long before it's necessary?

My EcoDiesel has 4.56 gears and 37s. That's about 9% more aggressive than stock 3.73 gears and 33s, so I should be experiencing his pain point even worse than he is.

Does he have "as much" experience off roading as you do? That could also explain it.

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