Putting Lower Gears in a 231j Tranfor Case UPDATED

Putting Lower Gears in a 231j Tranfor Case

• #1

Can anyone school me on what to exercise to get lower gears in the transfercase of a NP231?
I think that is what a friend of mine has in his 1994 YJ 4CYL 5speed.
He is an older guy that wants 36"tires. He has 34" LTB now. I am pretty sure he has 488 gears in diffs already and wanting lower gearing for off road.
I seen Tera Flex had a kit but looks like information technology is discontinued.
Any suggestions or options?

• #2

I don't know if anyone is even making iv:1 gears for 231'due south anymore.

Basically your options are:

one. Try to find a used four:1 ready

2. 231/231 doubler(or some kind of junkyard doubler combination)(probably also long for your setup)

3. d300 flip kit and 4:ane kit(if anyone nonetheless makes them, or try and buy used)

4. buy a rocktrack np241 out of a rubicon(there's ane on here for auction right at present) I personally recall they are overpriced. But given that there aren't many purchasable options, that might be the way to get.

5. Atlas.

• #3

Would the NP241 exist a directly bolt upwardly?

• #4

Would the NP241 be a direct bolt up?

Yes and no. The case bolts up, just the input shaft will need changed out. On the TJ's and LJ's the 4cyl'south were 21 spl and the 6cyl's were 23 spl. The automatic JK and JL rubicon cases had external splines on the input shaft. The manual had a standard 23 spl. The good news is You tin can pull the input shaft out of his current 231 and bandy it in to any of the case I mentioned. WORST case yous might have to bandy the 241 input begetting also, But that's an like shooting fish in a barrel bandy if needed.

• #5

Appreciate the info, Thank you!

• #6

The Tera Flex 4.i had a tiptop rev limit of 2500 RPM or something like that.
They were known for exploding.

• #seven

The Tera Flex iv.1 had a top rev limit of 2500 RPM or something like that.
They were known for exploding.

Hell, I'd accident that up loading on my trailer.....

• #8

The Tera Flex four.one had a top revlimit of 2500 RPM or something like that.
They were known for

I was wondering what the reason was that they quit making them.

Last edited: October 30, 2020

• #ten

I'd be looking at a blackbox/ecobox/klune reduction box + the 231 w/ skid yoke eliminator, or a flipped D300 (stock geared)

It'due south pretty dang overnice having 2 low range ratios for poking around in a transmission trans 4cyl rig

I am definitely familiar with doublers from the Yota world. I have 203/205 in my buggy now.
Only I know null about the blackness box, Klune, etc.... other than hearing there names. What I take to brand them work with his setup? Guessing Driveshafts and?

• #11

I am definitely familiar with doublers from the Yota globe. I have 203/205 in my buggy now.
Just I know nothing nearly the black box, Klune, etc.... other than hearing there names. What I accept to make them work with his setup? Guessing Driveshafts and?

I forgot almost those Nick. The ecobox is a good option. It's just a range box.

• #12

My buddy and I are collecting parts to do an Aw4, eco box, and 4:1 Dana 300 swap. This is going into a Toyota simply same concept lower gears behind a 4 cylinder also gotta accept front dig.

• #15

basically all of those options are a reduction housing that holds a NP231/241 planetary (the Ecobox is a DIY kit where you use a donor case). IMO information technology's a much cleaner and college value setup than the cut-case NP doublers that used to be common.

The advantage of using a D300 (or even a NP205) behind a reduction housing/clamber box is that the overall size is about the same as a stock NP231/241 (because of the the example configuration of a parallel gear driven example vs a chain bulldoze case).

it works out better in Jeeps which tend to accept long front end driveshafts and brusk rear shafts.

I know a NP205 is super-overkill for a 4cyl Jeep (and heavy) specially i that sounds to be stock-ish. Merely a Ecobox+Ford 205 is the cheapest, strongest, shortest setup y'all'll be able to to put together for a driver-drop 4 speed tcase.

Thanks Nick!
I volition definitely laissez passer this information on.

• #16

With 538s, dual 2.28, and 39 reds it'southward non plenty. Could endeavour it with a stock 300 before putting in the four:ane. Demand some training wheels as well.

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• #17

With 538s, dual ii.28, and 39 reds it's not enough. Could try it with a stock 300 before putting in the four:1. Need some training wheels too.

Manual trans?

• #xviii

Yes for now going with an Aw4 with a Toyota bellhousing.

• #19

Adding an automatic transmission to the mix will effectively "double" your gearing due to the torque multiplication of the converter. A rig with an automatic trans and a 75 to i crawl ratio will feel like a manual rig with a 130 or 150 to 1 ratio.

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Putting Lower Gears in a 231j Tranfor Case UPDATED

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