NP231 swap, SYE, 4:1 teralow etc

Hi all, I bought a lifted XJ, I think 4.5in. The four high has trouble engaging because of the driveline angles. I don't notice any vibrations though, even at highway speed.

It's a 96 5-speed.

I'm looking to pick up a transfer case with an SYE already installed. There are two nearby, both from YJs, but they're 23 spline so I think they should fit. The NP231 tags show mid-90's construction, so I think the shifters and VSS should direct swap too.

One is a regular 231 with SYE. The other has an SYE and a Teraflex 4:1. I read the Teraflex can blow up, but I'm not going to wheel or beat this thing too hard. The only reason I'm even considering the 4:1 is because the 5-speed has the 3.07 gear ratio that makes 4 low with big tires difficult to use.

Can you all help me:

a.) Understand everything I need to take into consideration when swapping the TC, like drive shafts ets.

b.) Whether I should run from the teraflex or just SEND IT

I've had my Tera 4:1 case for almost 20yrs now without any issues with it!

RCP Phx said:

I've had my Tera 4:1 case for almost 20yrs now without any issues with it!

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Thanks!

Among things to think about, if you are having trouble with shifting the T-case, seriously consider ditching the factory linkage and switching over to something like the Boostwerks linkage. However, in considering that, take into account your motor and trans mounts. The factory linkage is sloppy, and will tolerate slop in the engine/trans mounts. The aftermarket designs are more direct in their shifting and while this makes them work better when everything else is in good condition I would not expect them to tolerate the slop a factory linkage allows.

Anak said:

Among things to think about, if you are having trouble with shifting the T-case, seriously consider ditching the factory linkage and switching over to something like the Boostwerks linkage.

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Just another note....Driveline angles should not have changed the t-case linkage adjustment unless OP installed a t-case drop (or something else is amiss). I'd suggest trying to adjust the stock t-case shifter linkage to fix the current shifting issues.

If an aftermarket linkage is in the cards, I'd like to give a resounding yes on the Boostwerks linkage specifically. Theirs is the only one I could find that has the LH/RH thread adjustment stud for easy and precise adjustments. When I installed a Tera 2low...that required way more precise adjustment than I expected. The Boostwerks linkage made it work great.

A bit different view. What size tires? Why not regear? On a MT 3.55's should be good for 31's to 32's. Plenty axles out there. Some 4.10's that should be good for 32's-33's, possibly to 35's.

75SV1 said:

A bit different view. What size tires? Why not regear? On a MT 3.55's should be good for 31's to 32's. Plenty axles out there. Some 4.10's that should be good for 32's-33's, possibly to 35's.

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Depends on what type of wheeling you intend to do. I have an ax-15, 4.88s with stock t-case gears on 33s. In the rocks i would love more gearing. 4.10s with 35s you’d be doing a few clutches if you wheel in any technical rocks.

OP your stock rear drive shaft wont work since you are going to a sye. Front is ok.

75SV1 said:

A bit different view. What size tires? Why not regear? On a MT 3.55's should be good for 31's to 32's. Plenty axles out there. Some 4.10's that should be good for 32's-33's, possibly to 35's.

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You’re right. Rehearing to be closer to the stock band makes more sense. Only reason I’m considering this is the same guy has both TCs.

stockerwithalocker said:

Depends on what type of wheeling you intend to do. I have an ax-15, 4.88s with stock t-case gears on 33s. In the rocks i would love more gearing. 4.10s with 35s you’d be doing a few clutches if you wheel in any technical rocks.

OP your stock rear drive shaft wont work since you are going to a sye. Front is ok.

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Don’t people use a spare front for the rear or something?

saalmotrutta said:

Don’t people use a spare front for the rear or something?

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I do on mine. Its a Hack n Tap though. So, I had to adjust the length of the output shaft to match.
Also, I'd probably go a bit lower gearing for off road use. Still, don't know your tire size. I brought up those gearing as they can be found on stock axles. As suggest your could go with deeper gears. Also, I would not rule out getting the 4:1 TC. Much of this depends on tire size, intent of use and $$$ you want to spend.

saalmotrutta said:

Don’t people use a spare front for the rear or something?

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On an automatic, yes.

On a 5 speed the length is wrong, so you'd have to get it lengthened anyway. Might as well just buy a new shaft.

I have run standard NP231s for over 20 years. I run a 4.7Lstroker, AW4, and 4.56 gears. The thing I really love for the NP231 for the trails we have with tight turn radius's is the 2low conversion on the standard NP231. I have upgraded to 6 gear planetaries and wide chain. It really hasn't been needed but they dropped in my lap.

saalmotrutta said:

b.) Whether I should run from the teraflex or just SEND IT

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Depends on how the prior owner treated it. I ran one for years without issue, but I was light on the go pedal. Terablows were notorious for grenading the planetaries due to crappy bushings. If it's in good shape just keep it below 2500 rpm in 4Lo and don't shift past 2nd too often. That's pretty much the way I drove mine and it treated me well.

old_man said:

I have run standard NP231s for over 20 years. I run a 4.7Lstroker, AW4, and 4.56 gears. The thing I really love for the NP231 for the trails we have with tight turn radius's is the 2low conversion on the standard NP231. I have upgraded to 6 gear planetaries and wide chain. It really hasn't been needed but they dropped in my lap.

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2lo is a game changer on tight trails. 100%