Which transfer case is best?

[steffen707]

I would run trails in 4 low and just run in 4th on my sport JK when we were on the 2 track and slow down to 1st or second when there was some technical stuff or hills and I didnt have any problems. I am going with a rubicon for my JT because a lot that I would want to change is already done. I'm still building my off-roading skills (track days and drifting dont translate well when going over logs and rocks) and slow and steady works great for me. Bring on that 4 to 1, I have no problem using the "select speed" button or bumping it up a few gears to drive down the trails.

I with @homerun I also recall reading that the RockTrac is beefed up compared to the command track, though I dont remember what exactly the changes are.

At the end of the day, it depends on what kind of off-roading you want to do and how good you are at it. Mel is a pretty good driver from what ive watched him do in videos and KOH, carrying more speed is probably just fine for him. I think there is no problem with using the 4.1 to do the same stuff.

I have earned 0 out of 5 stars in off-roading, so i'll probably end up with a Rubicon after a short lease. I like the "most stuff is already done" for the build.
As always, thanks for the help @Malarkey21 and @homerun

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[5JeepsAz]

Gone Resto update... I'm considering adding overdrive to my 64 Gladiator. It would add one shift lever and offers 6 gears because it adds a high low to 1,2,&3. Not sure what I'm going to actually do; fun to think about. Anyway found cool pics!

 

[Ole Cowboy]

Rock Crawling Index:

The Jeep Rubicon 6 sp trans the ideal ratio would be about 66:1. This becomes our point of reference based upon the Rubcon with std trans.

NOW you have to factor: tire size (diameter) & RPM width of engine & HP curve & torque curve & weight of rig. This is where it gets dicey and very technical.

As you head towards a Crawl Ratio of 100:1 and beyond you are going to start needing some deep engine rpms, but you can mitigate that with taller tires, but then where is the torque/hp curve?

1) From a drive-train viewpoint, ideally, you want each set of gears (transmission, transfer case, and rear axle) to within .5 +/- .5 of each other. Example: Jeep Rubicon, 4:1 1st gear, 4:1 transfer case, 4.1: rear axle, this is EXCELLENT! Why is this? Strength and equal distribution – multiplication of torque in the driveline! Each component is of equal relative strength and torque multiplication is equal thru the drive train (4 x 4 x 4.1 = 66). Is it acceptable to exceed these values? Certainly, just remember added stress on components will require increased strengths and may lead to premature failure of certain components.

2) Why does the Rubicon do so well off road and especially in the rocks? Crawl ratio is balanced with the ability of the Jeep engine (RPM width, torque curve, hp curve) and the Jeeps weight and it all comes together quite nicely.

You have to consider all the factors. Pull the 4.0L out of the Rubicon and put in a good engine, say a high winding Chevy that does not get torquey until 2500+ RPM and its a whole different ball game.

The 4.0L delivers about 75% of its torque just past idle. Start going much beyond 3200 RPM and the engine is out of breath.

I like to use the RCI (Rock Crawling Index) to see what effect changes will make. This gives a relative score based upon a known performance index and it factors in tire size.

TM = TransMission (driven gear ratio, 1, 2, 3, etc)

TC = Transfer Case

AR = Axle Ratio

CR = Crawl Ratio

TD = Tire Diameter in inches

RI = Rubicon Index (2.12) Note this is a not fixed number as it is based upon OEM specs for the Rubicon w/NV3550 transmission. You could use anything you wanted, but the Rubicon is well known and this provides an index of known performance on which you can compare.

RCI = Rock Crawling Index

TM x TC x AR = CR

CR divided by TD = RI

RCI = RI / 2.12

TM (transmission ratio) = 4.01 < enter data

TC (transfercase ratio) = 4.00 < enter data

AR (axle ratio) = 4.10 < enter data

CR (crawl ratio) = 65.76 TM x TC x AR

TD (tire diameter, inches) = 31.00 < enter data

CR 65.76 / TD (31) = 2.12 RI (Rubicon Index)

4:1 TM x 4:1 TC x 4.1 AR = 66 CR/31 TD = 2.12 = OEM Jeep Rubicon

RCI = 2.12 (rock crawling index FOR the Rubicon), now enter your data from your rig and compare with the Rubicon or ???? what ever you chose.

NOTE: as you go up in tire size you need to increase the index slightly to compensate for the added mass the larger tires bring. Start adding extra weight, wider tires (increased CoF), trail tools etc etc and the OEM Rubicon 2.12 will not cut it so the RCI has to continually drift upward.

Throw on a set of BFG KM2's in 37x12:50 and life will be a LOT better with a 4:88 axle ratio, everything else staying the same.

 

[MrKnowitall]

In mud, I feel the 4:1 low range is lousy. Running high range leaves you short on wheel torque when things get really sticky. In low range you cant get the wheel speed you need, even if only momentarily. Answer? Stak 3-speed.

 

[NC_Overland]

Not really, 4 High does put a lot of strain on the driveline and requires a lot of engine power. If you're at moderate speeds on the trail 4 High is still geared too high but the 4 Low in the Rock Trac is too low. I find that the 4 Low in the Sport hits the sweet spot just right.

There are some guys with the Rock-Trac case that just use 4 Low and then select a higher gear if they've got a manual transmission. That works OK in limited areas. I'm just a big fan of the 2.72 low range in the Command-Trac case.

Yeah, when I had my JKU Rubicon, it was a 6 speed. I lived in CO most of the time I had it, but I still started off in 3rd or 4th gear most of the time. I wouldn't have liked it as much with an automatic, but it did fine with the manual. I never needed to go faster in 4lo than what it would do in 6th.

 

[Blade1668]

Well since this was dug up. Yes the NV241 Rock-Trac is stronger than the NV231 Comand-Trac that was in the "O.G." Rubicon TJ's vs all other TJ's, YJ's, XJ's ect. 231s was used in 1/4 ton though 3/4 trucks... If I'm not mistaken (3/4 ton) now in the case of later Jeep's T-case I don't know when or if across the lines went to NV 241 T-case over NV 231J. Now the STAC would be a hell of a anti-theft set up with a manual transmission too. Throwing in a #4. The 242 full time T-case or larger brother (?) I would not have been surprised to hear it was in the Overland models like in upper models of XJ, G.C. ECT that got the full time T-case, at the cost of MPG (?)​

 

[MrKnowitall]

Well since this was dug up. Yes the NV241 Rock-Trac is stronger than the NV231 Comand-Trac that was in the "O.G." Rubicon TJ's vs all other TJ's, YJ's, XJ's ect. 231s was used in 1/4 ton though 3/4 trucks... If I'm not mistaken (3/4 ton) now in the case of later Jeep's T-case I don't know when or if across the lines went to NV 241 T-case over NV 231J. Now the STAC would be a hell of a anti-theft set up with a manual transmission too. Throwing in a #4. The 242 full time T-case or larger brother (?) I would not have been surprised to hear it was in the Overland models like in upper models of XJ, G.C. ECT that got the full time T-case, at the cost of MPG (?)​

When the NVG231 was used in 1/2 ton applications, it has some stronger internals than in the Jeep and GM S trucks. You could, however retrofit some of these parts into the Jeep case. Yes, the 241 was used in 90s 3/4 tons, but the larger case allowed it to fit the 4:1 low range (with some casting changes). I don’t believe the 242 will fit a 4:1 planetary. I would still like to have one in a JT though, especially with the MT.

 

[@californiajeeping]

You can't just run 4 low in 4th gear there's a limit for the planetary gears speed it will shorten it's life drastically.


The speed should be listed in the manual for a jt. Wheel speed is just as hard as ground speed if a 35" tire spins at 50 in 4 low and snags a root your lucky if just an axle shaft breaks. Spider gears are probably the weakest link on our jeeps.

 

[whiteglad]

If you "scroll back" 4+ decades, the strongest and most desirable transfer case was the gear drive, iron case NP205, which had 1.96 low range. People came to prefer the 2.72 of the planetary drive aluminum cased units for their low range ratio, if not strength. My experience with all three ratios led me to prefer the 2.72 low.

 

[MrKnowitall]

You can't just run 4 low in 4th gear there's a limit for the planetary gears speed it will shorten it's life drastically.


The speed should be listed in the manual for a jt. Wheel speed is just as hard as ground speed if a 35" tire spins at 50 in 4 low and snags a root your lucky if just an axle shaft breaks. Spider gears are probably the weakest link on our jeeps.

That low range planetary can whiz along just fine. Owners manual says not to exceed 25mph in L4.
35’s are about 600revs/mi, so @25mph in Low range... 25/60*600*4.10*4*.72(6th)=2952rpm. To spin at 50, you’d gave to wrap 6th gear to 6 grand! With the auto it’s slightly less, but you’d have to stabd on it until it upshifts through every gear. If thats how you roll... yes, stuff will break.

 

[BearFootSam]

Not really, 4 High does put a lot of strain on the driveline and requires a lot of engine power. If you're at moderate speeds on the trail 4 High is still geared too high but the 4 Low in the Rock Trac is too low. I find that the 4 Low in the Sport hits the sweet spot just right.

There are some guys with the Rock-Trac case that just use 4 Low and then select a higher gear if they've got a manual transmission. That works OK in limited areas. I'm just a big fan of the 2.72 low range in the Command-Trac case.

Old thread but I'd like to add that it's not just about needing the power but having control. I've been on narrow shelf roads in Colorado where there is essentially a wall on one side and a cliff on the other. All of the UTV traffic going way faster than is respectable chew up the road leaving rock steps to surmount. If you hit those too fast you will bounce up and potentially lose your line/control. In such a situation by engaging 4-Lo you can crawl at 1mph bringing the front wheels over the step with precision. A low enough crawl ratio negates some of the need to use both feet to manage the sudden decrease in effort with the front axle completes the climb.

Back in the Army we would train on a difficult offroad course in humvees. One of the obstacles was a two foot vertical wall. The technique was to but the front wheels up against the wall and slowly power up and over letting the rear wheels drive the front hard into and up, over. Of course given the throttle input needed to do that if you didn't have your left foot on the brake, as soon as the front tire hub line rose above the edge the vehicle would lunge forward without control. With a low ratio crawl gear it would have been possible to overcome the obstacle gracefully without dual footing.

This may be an edge case example, but such circumstances are what separates the most capable vehicles from the ones that have to turn around. A bit of over kill capability wise also translates into a margin of safety which when far from help or when the consequences of an error are high, is a worthwhile attribute. Sure CUVs have made the trek over some challenging trails out west but they will never be able to do so as safely and assuredly as a more capable 4WD. When conditions deteriorate and you suddenly find yourself over your head, that margin makes all the difference.

Conversely, a low crawl ratio is vitally important on down slopes. Descending some of these treacherous trails is a magnitude safer, when you can allow engine braking to manage your speed. Engine braking is far less likely to break traction which would cause a loss of control.

I like to use my vehicles to get far out in the backcountry to camp. Depending on your use case a low crawler gear may not be necessary. For those of us for whom it is, there are very, very few vehicles on the market that can approach the technical capability of a jeep.

 

[troverman]

I like to use my vehicles to get far out in the backcountry to camp. Depending on your use case a low crawler gear may not be necessary. For those of us for whom it is, there are very, very few vehicles on the market that can approach the technical capability of a jeep.

It seems the new larger Bronco can match the Jeep. There are obviously many similarities. The biggest difference is the IFS front suspension on the Bronco. If you have lots of money, the Mercedes G-Class may also be able to match it. Possibly a Colorado ZR2 truck, and if you have the room, a RAM PowerWagon.

 

[BearFootSam]

It seems the new larger Bronco can match the Jeep. There are obviously many similarities. The biggest difference is the IFS front suspension on the Bronco. If you have lots of money, the Mercedes G-Class may also be able to match it. Possibly a Colorado ZR2 truck, and if you have the room, a RAM PowerWagon.

As cool as the power wagon is, it's a bus compared to the jeep and that will cut your line choices pretty significantly in tight spots. Thinking of passing with PW on some of the trails between Silverton and Lake City CO, it would get pretty sketchy. I like that I can hang my head out the window and clearly see my front tire and know when it's too close to the edge.

 

[troverman]

That's why I said "if you have the room." There are some times the long wheelbase has an advantage, but the Jeep has great trail dimensions.
My absolute favorite vehicle for trail work would be a 1994-1997 Land Rover Defender 90. As good of trail dimensions as a 2-door Wrangler, but with a stronger chassis, small V8 engine, manual or automatic transmission, permanent 4x4, gear-driven transfer case with 3.32:1 low range, 4-wheel disc brakes, locking center diff, solid, fully-floating axles front and rear, matching offset front and rear diffs for better clearance, long travel coil suspension all around and better flex than anything without an unlocking sway bar. Stock tires were 31.6" with plenty of room to accommodate more without mods. The problem is that these trucks cost a mint to get a nice one today.

 

[bleda2002]

It seems the new larger Bronco can match the Jeep. There are obviously many similarities. The biggest difference is the IFS front suspension on the Bronco. If you have lots of money, the Mercedes G-Class may also be able to match it. Possibly a Colorado ZR2 truck, and if you have the room, a RAM PowerWagon.

Perhaps you mean the bronco raptor which may honestly be the best stock factory off roader. The regular big bronco is somewhere between a 4 runner and a Rubicon in terms of actual capabilities and is let down by it's horrible down travel(even with sway bar disconnected) and extremely weak tie rod and rack. Now with mods the jeep is still easily the king as the SFA lends itself to cheap easy lifts and components that just can't be done on an ifs truck with out crazy amounts of money.

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