question to the op.. are your axles geared? because it has been my expierance with my xj that an auto 4:10s and 32s i rarly feel that i "need" a steeper crawl ratio.. and my "jeep thing" build i'm going 35s with 4:56s and the cherokee driveline... with the stock 3:55s low wasn't enough..i'm just making sure you put ducks in a row here... gear axles first

 

i have 410's and 35's its ok i would like to get a bit slower if i could . i dont want to buy gears so i figured heck why not go dual cases. pluss it looks cool in the truck and buildng a cross member is not to hard.

i dont know enough about the cases yet to fully understand what part of each one i need and why and ware i need to make a plate to fit them both together, i know i dont need to forward out puts tho. .

 

I would definately gear your axles.. 4.10's and 35's is not fine on the trail... trust me I know. Once you install a doubler you will learn that gearing is where it is at. I am running the dual 231's and 5.13's in the axles on 36's.

On my truggy I will be running a 4.3 (different torque curve, as well as rpm range) 700r4 with 4.56's and 2o3/300 doubler. on 39.5's. The torque converter makes up for the differnet axle ratios by multiplying the torque there.


Also by having the proper gearing in axles and t cases, reduces the change of having breakage issues. You dont need to use the skinny pedal as much

 

^x2
Low gears are king on trails and rocks! I would love to have 5.13s in my axles instead of the 4.88s and after running a doubler in my built Blazer I would love one in my XJ, a 231/300 with a 4 to 1 kit in the 300 would give my XJ a 203.35 to 1 crawl ratio and for most rock work the 4 to 1 ratio would give a crawl ratio of 74.76 to I and for snow wheeling the AX15 first gear with the np231 and 4.88 gears gives me a 50.84 to 1 ratio. I think that would be the ultimate gear set up.

 

I think that might be a bit low. I have a 128 crawl ratio and it is plenty slow. Right now I have a 2.7, 3.8 and 10.38 ratio available. The 3.8 is good for general small rock work, but the 10.38 is not too slow. I think with a 200 crawl ratio that you would constantly be after the higher gears in the tranny.

 

Well, I have 4.88s and a AX15 that has a 3.83 first gear ratio, as far as the doubler would go the ratios would be np231= 2.72 to 1 ratio D/300= 4 to 1 ratio 2.72 x 4 = 10.88.
So my AX15 with a doubler and 4.88 diffs give me the option of going as low as 203.35 to I.
I really don't think I would need to go that low, but I like the idea of being able to if I wanted.
The 2.72 and the 4 to 1 would be the most useful, and the 10.88 to 1 would not be used much, if it would be used at all, maybe in second gear 2.33 x 10.88 x 4.88 = 123.71 to 1 would be about perfect for bigger rocks.

 

I use the 10.38 more than I thought I would. When I took the wive out in the rocks it just made them smooth, took them at an idle and made it enjoyable for her. I gained a new wheeling partner out of it.

 

heres my 231/231

 

Good job! It is good to have a wife that enjoys your hobbies.
Yeah, by using the super low gearing that the doubler provides it makes rocks a lot easier and smoother. Less smash and more finesse = less breakage and more capability.

 

Yes, even though I paid a lot for the tcase, which was no big deal at the time, I would rate the low gears right up there with any other mod you can do for rocks We went to a dealership last night for a free give away and the guy asked what we drove. I said a Jeep and didn't say much about it. She jumped right in and said "This Jeep crawls rocks". Made me proud.

 

more than likely you have an np-231 if you crawl under there should be a tag with all the info on it on your t-case

 

well 35's my 410's and a my 231 in snow were great today. i can roll as slow as 3mph if i idle up a bit. so if i went dual cases and had a lower low when needed i'd like to try that for a while . i was crawling in 1-3ft no prob . but i was able to stay on top too. it was a bit sugary this morning but once it warmed p some it was easy sailing

 

can some one post a pic from the bottom veing directly up? i see ware the two cases met now. but am curious dose the drive line tot he front still come out of the original case?

 

the first case (bolted between trans and second case) is just a low range high range box. the second case is the 2/4wd box with low as well.

 

oh ok that helps i am searching dual t-case pics to get a better idea. i picked up aluminum I'm going to cnc it at work. so it will be a exact plate & I'll always have the program to make more.

anyone have a pic for what the did for the shafts and fluids? do i need passages for it to flow between the two cases? or will they be independent of each other fluid wise?

also another question. can i use the 231 wit the aw4? the aw4 will bolt to the Toyota engine i plan to run plus a bell housing but the jeep running gear will say jeep. if that makes sence?