In your opinion would a NP 241 with Rubicon 4-1 low range be strong enough for something like this? Does the NWF ECO box have provisions to bolt up to a NP241. Although the 205 is bulletproof, it is also heavy and only has a 1.96-1 low range. Double 241 reduction is 5.44 and Rubicon plus regular 2.72 NP 241 is 10.88. Finally double Rubicon would be 16-1. You could get over a 120-1 crawl ratio with 4.10's, a 4L80E and dual Rubicon planetaries. Is that excessive?
I like your thinking here. My head isn't clear at the moment and I'm not sure if math is correct, but it sounds close. I'll say this- I have a Jeep Rubicon that I bought new off the lot back in '05. It had the 241 with 4:1 low range. Factory setup with 4.10s was I THINK a 72:1 crawl ratio if I recall correctly. I have essentially broken all the Rubicon parts and upgraded or replaced, and built that rig up from scratch to what it is now. When I put 33" tires on with factory 4.10s, I lost 6th gear entirely and 1st became a dedicated starter gear. I HATED it's performance. In 4:1 low range, crazy as it sounds, I hated the 4.10s and 33s. Obstacles that I could idle before in 1st gear now took throttle to get over. I was not happy in high range on the street or low range off road. I put 4.88 gears in the diffs and that brought it back down to better/lower than stock ratios. I have passing power in 6th on highway and can idle again in 1st in low range. I had the finesse and control back again that I'd missed prior. Due to chasing odd vibrations I narrowed it down to a problem with the input bearing in the factory 241 case. It's a double ball bearing roller setup with a plastic cage. Over time and wheeling, one of the sprockets or teeth in the plastic cage had failed and the balls would occasionally skip a tooth. I could feel this through driver seat and went crazy until I tore it all apart and found the problem. Once I found it, I totally rebuilt the 241 case with all new bearings and seals. I sold it and replaced it with an Atlas. I liked the 4:1 so well that I went with the 4.3:1 Atlas case. Best move I ever made on the Jeep. I LOVE that thing and the ability to have 2wd low range, and front wheel drive on it's own. Crazy how much I use it actually. This is why I wanted the same ability with split axles in the Suburban. I also loved the low range crawl ratio but- odd as it sounds, wanted another "middle" gear. There are times when high range is too high but low range is too low- like moving between trails or sections of trails that are long before next obstacle or slow technical spot. Running in 5th low range kinda sucks but 1st high range isn't low enough. Because of that, I wanted a 3 speed minimum in the Suburban. That's where the NWF Eco box came to play. With both boxes in high range I have 1:1 ratio. With 205 in low range, Eco box in High range, I have 1.96:1 mid range. With Eco box in low range and 205 in high range I have 2.72 low mid range, and with both the Eco box and 205 in low range (double low) I have 5.38:1 double low range. A 4 speed box. In the Jeep with 4.46 1st, 4.3 Atlas and 4.88s in diff I have 93.5:1 crawl. Manual trans 6 speed. In Suburban with with 4L80E and 2.48 1st gear, 5.33 double low gear and 5.38s in diffs, I'd have 71.1 double low- and with autos they "say" the slush box/torque converter basically doubles it, it would be 142.2:1 effective overall crawl. I have yet to see if this performs as I hope.
So to your question- is it excessive- that depends. With the Jeep and prior to Atlas with just the factory Rubi 4:1, in Moab on various trails around Poison Spider and the loop area there, there was times where 1st low was great for crawling UP the steep stuff, but going back down was a different story. 1st on some of the steeps there was too low and caused loss of traction because the Jeep was turning slower rpm than the slick rock could hold at such steep angles. As a result, I'd slide down out of control despite the low gearing. By switching to 2nd or 3rd, I could match rate of decent slide with rpm at wheels and maintain traction and control. Where I wheel here in WA the most, I like 1st low on the steeps as it's different terrain and 2nd or 3rd is too fast to control. When I slide it's due to loose rock in 1st but soon as I catch traction again it crawls and sticks maintaining control. In snow, it's a different story. Aired down to basically zero pressure with as big a footprint as possible, and in 1st low, sometimes I want a lower crawl than what I have at 93.5:1. Long story short- would you use 120:1 or better much? Probably not much- but the ability to get there when needed would be priceless. you'll spend majority of time in the mid range ratios but having that "extra" edge when needed can mean the difference in pulling winch line or not. As much winching as I do, I like that "edge" when I can get it.
As to the "strong enough" question. It's an aluminum case, but yes, I think it's strong enough. Having done SYE conversions on 231 cases and seeing differences in the 241s as well, the 241 is just bigger, wider, stronger, better overall. 231 is 3 pinion planetary??? where the 241 is 6 pinion planetary. The Rubicon 241 is a big 4 pinion planetary but big planet gears. More surface area. The 6 pinion planetaries in the non-Rubi 241s are extremely strong, and in stock form are found in the diesel trucks. Those same cases are found in the sled pulling trucks unmodified despite the massive horsepower and torque they put out. I don't know if NWF builds and adapter to mount two 241 cases together, but I know they could if they don't. Would it work- yes. The question would be is the input shaft large enough to handle the torque multiplication of the doubled boxes. They make a big input for their "Titan" line but not sure how that relates to compounded 241s. The 205 is heavy yes as it's all cast, but it's gear drive and you gain the split axle ability. That is not possible with a doubled 241 to my knowledge. I could be wrong there but not sure that you can do it with chain drive. Never looked. The 241 chain is big/wide though and with 6 pinion planetary is capable of handling big torque loads. I have to believe it's possible yes. Is it necessary? Doubtful. Excessive? Probably. There is another product out there for Jeeps called the "Rubicrawler". It's a 10.88:1 reduction box capable of low crawls. I know a few guys who have it, and wish they never did it as it's too low for where they wheel and they can't or don't use the 10.88:1 ratio. I personally have never done an auto trans with low gearing, only been manuals. I'm curious where my doubled box will work with the 4L80e. In my mind, it will be perfect for the Suburban HD, and I can't wait to see how it plays out in reality once built. I will say having split axles and the ability to run front or rear locked or unlocked independent of the other is priceless.
Sorry for long winded response, hope that helps or at least gives something to think about.
Best of Luck,
Mike
