Why a doubler?

[Mudderoy]

A recent post was asking about putting a doubler on a NP242 transfer case. It dawned on me, WHY?

I mean I know it allows you to get more power to the ground, but 4 wheel low is well really low. Why would you need it, 4 times(?) lower than that?

[4.3LXJ]

That is a good question Tony. The answer is, you don't in your area since you mainly do mud when you wheel, which requires a higher tcase ration than in rocks for instance. In rocks, it is not a question of power as much as speed. When you take a 2.0 ratio rig, like say a CJ or early Bronco into a place like the Rubicon with a standard tranny, you take a lot of miles off a clutch by the end of the day. When Jeep went to the 2.72 ratio, it was better, especially with an automatic. But in the real ruff stuff, even that is a bit fast and can get an auto tranny very hot, and you end up standing on the brake a lot and on the gas after wards. The most ideal ratio for the all around rig is 4:1. Rocks have gotten bigger and suspensions more supple so now a trail that was impassable without a winch forty years ago is commonly done in a DD XJ with a 4.5" lift and a rear locker. That is why the Rubicon models have the 4:1 ratio in the tcase. But if you really want to take it easy on your rig, the really deep ratio of 10:1, recommended by Advance Adaptors for an auto tranny is the real ticket. You can idle through almost anything, with just a feather weight tap on the gas on large obstacles, while maintaining much more control than with the higher ratios. I was really pleased with how the Atlas performed, and the wife enjoyed it too.

[xj4life2]

nicely done Steve , I haven't any experiance with the 231 doubler but that Atlas is the ticket !!!

[Mudderoy]

That is a good question Tony. The answer is, you don't in your area since you mainly do mud when you wheel, which requires a higher tcase ration than in rocks for instance. In rocks, it is not a question of power as much as speed. When you take a 2.0 ratio rig, like say a CJ or early Bronco into a place like the Rubicon with a standard tranny, you take a lot of miles off a clutch by the end of the day. When Jeep went to the 2.72 ratio, it was better, especially with an automatic. But in the real ruff stuff, even that is a bit fast and can get an auto tranny very hot, and you end up standing on the brake a lot and on the gas after wards. The most ideal ratio for the all around rig is 4:1. Rocks have gotten bigger and suspensions more supple so now a trail that was impassable without a winch forty years ago is commonly done in a DD XJ with a 4.5" lift and a rear locker. That is why the Rubicon models have the 4:1 ratio in the tcase. But if you really want to take it easy on your rig, the really deep ratio of 10:1, recommended by Advance Adaptors for an auto tranny is the real ticket. You can idle through almost anything, with just a feather weight tap on the gas on large obstacles, while maintaining much more control than with the higher ratios. I was really pleased with how the Atlas performed, and the wife enjoyed it too.

How does the automatic get hot with the 2.72 and not with the 4:1, and does that mean that a 4:1 would be a 10.88 ratio (assuming 2.72 transfer case)?

[4.3LXJ]

Here is a vid of an obstacle on the Baltimore Trail, off the the upper end of the Fordyce Creek trail. I have posted this before, but this is a good illustration of what a really deep ratio can do.

[IMG]http://i649.photobucket.com/albums/uu215/warriorsuspension/Fordyce%20Trails/Baltimore%20Trail/th_MVI_1397.jpg[/IMG"]Image hosting, free photo sharing & video sharing at Photobucket

At the end of the vid, there is an 18" high chunk of granite that would make you put the gas to a rig with a 2.72 ratio. In this case, even with only 31" tires, it was a cake walk. With just a slight tap of the skinny pedal, if you do the math, it gives you a slow steady 500 hp at the rear wheels.

[Mudderoy]

Here is a vid of an obstacle on the Baltimore Trail, off the the upper end of the Fordyce Creek trail. I have posted this before, but this is a good illustration of what a really deep ratio can do.

http://i649.photobucket.com/albums/uu215/warriorsuspension/Fordyce%20Trails/Baltimore%20Trail/th_MVI_1397.jpg (http://s649.photobucket.com/albums/uu215/warriorsuspension/Fordyce%20Trails/Baltimore%20Trail/?action=view&current=MVI_1397.mp4)

At the end of the vid, there is an 18" high chunk of granite that would make you put the gas to a rig with a 2.72 ratio. In this case, even with only 31" tires, it was a cake walk. With just a slight tap of the skinny pedal, if you do the math, it gives you a slow steady 500 hp at the rear wheels.

Gotcha, ok so no stress to the automatic (or clutch on a standard) means cooler and longer life.

I've notice that with the 4.56 gears in my XJ I don't have to use much skinny petal to get up and over things, so it makes sense. I love those gears on and off road.

[jeepxj95]

or if u do some yard work with ur xj like i have and dont want to run the risk of brankin any front end stuff or streach the chain. u could use the doubler in 2 wd as a 2 low in the 231 or in the 242 u could use it as a full time low. like with the old np 203 case. would be great for winter. i have always liked the 2 low option or even better the full time low range. but then we get snow here and even in town if we get a lot some times the city dont plow untill noon or later. fun to play in but not when u have to get to ur job or take ur wife to work.

[07Negative]

Is the factory Rubicon transfer case a bolt on for a XJ with a AW4?
When the time comes. I was kicking around the ideal of the Tera Flex 4.1 transfer case.
I'm not well verse or finically ready to even think about my T-case yet. But would
Like to have a goal/ideal in mind for when the time comes.

[4.3LXJ]

The Rubi tcase would be a bolt in for you. It has an advantage over the Tera Flex case in that it has a heavier chain in it.

[07Negative]

Nice to know! So I'm guessing a 1.5" instead of the 1" chain? Kinda like the dodge t case fitted for a jeep?

[4.3LXJ]

Not sure on the exact width, but a heavier chain anyway than what we have. An S10 231 has a wider chain than we do also. The parts interchange.

[prerunner1982]

Is the factory Rubicon transfer case a bolt on for a XJ with a AW4?
When the time comes. I was kicking around the ideal of the Tera Flex 4.1 transfer case.
I'm not well verse or finically ready to even think about my T-case yet. But would
Like to have a goal/ideal in mind for when the time comes.

I don't guarantee anything, but if I believe I have heard that the TJ tcases are clocked differently than the XJ. If so, not sure what kind of interference this may or may not cause.

[4.3LXJ]

I don't guarantee anything, but if I believe I have heard that the TJ tcases are clocked differently than the XJ. If so, not sure what kind of interference this may or may not cause.

That is correct. You may need to run a tcase drop.

[XJ4IV]

and here is the REALL question... what differential gear ratio is equal tohaving this doubler?
Im getting ready to install 5.13's and I think that a gear ratio THAT deep oughta give me JUST enough crawl... especially for 60's

[4.3LXJ]

OK, let's do some math. I think you will be surprised.

You have 2.7:1 now with 3.55:1 gears. Now we will take that 3.55 and multiply that by another 2.7, the ratio of the doubler, and get 9.58:1. The deepest you can go with a D60 is 6.67:1

[Mudderoy]

OK, let's do some math. I think you will be surprised.

You have 2.7:1 now with 3.55:1 gears. Now we will take that 3.55 and multiply that by another 2.7, the ratio of the doubler, and get 9.58:1. The deepest you can go with a D60 is 6.67:1

lol you are a cruel, cruel man! :patriot:

[4.3LXJ]

lol you are a cruel, cruel man! :patriot:

Yeah, but it is fun :p

We didn't even get to tire size yet :D

[Mudderoy]

Yeah, but it is fun :p

We didn't even get to tire size yet :D

lol, yeah tire size (a requirement for Dana 60's) did cross my mind when I was typing in that post!

[4.3LXJ]

Actually, what he had in mind was how they used to do it. Jeeps came with 5.38s and 29 inch tires and a 2.0 in the tcase. But as tire size went up a little, the tcase went to 2.7. Now you would need gears that cannot be made to do the same thing.

[Mudderoy]

Actually, what he had in mind was how they used to do it. Jeeps came with 5.38s and 29 inch tires and a 2.0 in the tcase. But as tire size went up a little, the tcase went to 2.7. Now you would need gears that cannot be made to do the same thing.

Can you re-gear the transfer case to accomplish the same thing?

[4.3LXJ]

I am not sure about the parts for this, but I think you can to a certain extent. The 4.0 parts are very similar to the 2.7 parts and may interchange. But I don't know if any others have figured that out yet. I suspect they are though because of what Klune V and Advance Adapters offer. However for our tcases 4.0 is the limit. If you want creepy crawly gears you need an extra set of gears, hence the doubler.

[XJ4IV]

OK, let's do some math. I think you will be surprised.

You have 2.7:1 now with 3.55:1 gears. Now we will take that 3.55 and multiply that by another 2.7, the ratio of the doubler, and get 9.58:1. The deepest you can go with a D60 is 6.67:1

WOW Sooo basically then my NEW setup would offer...37.39:1 if I had a doubler...holy crap... is that even moving?
in 4 low id have 5.13*2.7 which is 13.85:1

[4.3LXJ]

Yeah, it is moving. You would be surprised at how useful that really slow speed is in the rocks. It makes everything smooth and much easier than with just 2.7:1. My Atlas has the best of both worlds. 2.7. 3.8 and 10.38:1 I use them all depending on the situation. But the slow even crawl is keeping my Turdy five together with a locker. No jerky stop and go wheeling.

[bigjim350]

Steve already metioned this. The type of gearing you need depends greatly on the terrain you wheel in. Down here in the mud the rubicon guys have a dumb look on there face when a xj makes it through the mud easy, while they are slowly spinning there tires and not moving. Low geared t-cases are cool, but make sure its what you NEED before you do it.

[4.3LXJ]

Very true. The Rubi tcase NP241 is too low for good mudding. 2.7 is passable but the best is the old school 2.0 ratio. The rage now is doing rocks, so that is where the industry has been going for the past few years. Like Jim says, build for what you will do. But I like to do it all, so that is the rational behind the Atlas I bought.