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  #1  
Old November 13th, 2018, 08:34
Prefontaine Prefontaine is offline
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AX-15 + NP-242, Revisited

Hi everyone,

Sorry, this issue *has* been discussed a few times on various forums, but a lot of the continuity on this is 5+ years old. And I can't seem to make a new post on archived threads.

My XJ is: a daily driver, 95%+ on road only, in great shape with 180,000-ish miles. AX-15 with NP-231 Tcase. It will remain a DD, and I'm just refreshing items to keep it as a live-able DD that is capable of getting me across various low-threat, non-technical off road locations. Also has a 3.5" lift with 31x10.5 tires.

My question is this: though the NP-242 swap is certainly possible (I've had the Tcase since 2013, and got it with the intent of putting it in my old AW4 XJ when I lived in AK), some people say it works great, while others (one guy in particular online, can't remember his username) says it will create too much "slop" based on an open diff introduced at the Tcase. I understand this may be true in principle, but I'd like to hear from those who have actually been running this (@foxwar71, I tried to PM you but your inbox is full...would also welcome any feedback from anyone else who has at least tried this / ridden in one).

More specifically...

1) Is the "slop" with an AX-15+NP242 really that noticeable?

2) Is it present only when in Full Time 4WD, or in all modes? My hope is that any sub-optimal issues would only occur in FT4WD, and otherwise it'd feel like a standard 231 Tcase.

I'll eventually be moving back to New England, and would love the FT4WD option after driving a 231 equipped XJ in AK for 3 years. PT4WD works ok, but it's not a perfect solution to on-road conditions where available traction changes rapidly.

Thanks in advance.
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Old November 13th, 2018, 12:36
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themauler themauler is online now
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AX-15 + NP-242, Revisited

Why would any tcase manufacturer make something with noticeable slop in it? The rear axle is getting strait through power from your transmission output in all tcase positions besides neutral.

The only scenario I can think of that might feel different is in full time 4wd and taking a u turn on the street but it won’t hurt anything.

I think you are over thinking this. I wouldn’t hesitate to put a 242 behind an ax15 and run full time down the road.


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Old November 13th, 2018, 21:56
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ehall ehall is offline
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Re: AX-15 + NP-242, Revisited

Differentials do not shed energy they direct it to the path of least resistance. Does the diff in your axle have too much slop?
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Old November 14th, 2018, 07:15
chris420 chris420 is offline
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Re: AX-15 + NP-242, Revisited

I have 242 AW4 combo and wheel hard all the time Rubicon, Fordyce and Barret Lake. The only slop I feel is my tires spinning.
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Old November 14th, 2018, 07:37
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Re: AX-15 + NP-242, Revisited

Quote:
Originally Posted by ehall View Post
Differentials do not shed energy they direct it to the path of least resistance. Does the diff in your axle have too much slop?

I believe he's talking about the (effective) spider gear assembly between the front and rear outputs. If you grab both tires on an open diff rig there's definitely a little slop between them.

IIRC only the front end is affected by it and it is a non issue. I'd be comfortable giving it a try without getting personal experience on the issue.
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Old November 14th, 2018, 08:00
Prefontaine Prefontaine is offline
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Re: AX-15 + NP-242, Revisited

Thank you for the replies everyone. I think there's a misunderstanding though with what I'm asking. I'll do my best to explain.

Quote:
Originally Posted by themauler View Post
Why would any tcase manufacturer make something with noticeable slop in it? The rear axle is getting strait through power from your transmission output in all tcase positions besides neutral.

The only scenario I can think of that might feel different is in full time 4wd and taking a u turn on the street but it won’t hurt anything.

I think you are over thinking this. I wouldn’t hesitate to put a 242 behind an ax15 and run full time down the road.


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A manufacturer certainly wouldn't want to put a subpar product or combination in a vehicle; I agree. This is why the NP242 was only offered with the AW4, not the AX-15. See below for numerous comments on why the AX-15 and NP-242 are a "bad idea."

Quote:
Originally Posted by ehall View Post
Differentials do not shed energy they direct it to the path of least resistance. Does the diff in your axle have too much slop?
My differential is currently fine; my only concern is with an AX-15 and with an NP-242 in full time.

Quote:
Originally Posted by chris420 View Post
I have 242 AW4 combo and wheel hard all the time Rubicon, Fordyce and Barret Lake. The only slop I feel is my tires spinning.
Right, you have what the factory offered. No surprise that it works well! AX-15 with NP-242 was never an option.

Quote:
Originally Posted by cal View Post
I believe he's talking about the (effective) spider gear assembly between the front and rear outputs. If you grab both tires on an open diff rig there's definitely a little slop between them.

IIRC only the front end is affected by it and it is a non issue. I'd be comfortable giving it a try without getting personal experience on the issue.
Yeah, I'm thinking that I just need to do it and see how it goes. I was hoping that the ~3 people who I know have done it in the past (from reading previous posts) would chime in.

-----------------------------------------------------------

Comments from other threads on the internet regarding this:

Quote:
IIRC I was told that there is a bit of 'slack' in a NP242 due to the clutches or something, I forget the details. It was mentioned that driving with this in a 5-speed would be more noticeable and possibly put more stress on the case when shifting between gears than an automatic trans would, which could explain why the 242 wasn't available behind any of the manual trans XJs.
(note that there are no clutches in the NP-242, but the concept of slack still persists)

Quote:
I did this swap years ago. It's doable with the correct input shaft on the T-case. You'll need to change the linkages that connect the lever to the t-case.


Is it workable? Very. Do I suggest it? No.



Because of the center diff inside the 242 .... there is always some slop/backlash. It is not noticeable with an automatic, however, as you shift with a standard trans, you will hear and feel the gears loading & unloading. Will not hurt anything, but it can be a bit annoying to some people.
This same sentiment is in a few different threads, all from the same guy. This is what I was most concerned about.

Quote:
The gears in the center section will "float" because they are not tightly intermeshed. So what I am describing is simply the noise/action of the gears re-meshing to each other. An automatic trans will almost always have positive pressure on the gears as you accelerate or decelerate. However, the clutch of a manual allows complete disengagement of driveline torque (other than centrifugal rotation). That is how you feel/hear the slop I am referring to. It's the gears engaging against themselves again and it takes like a microsecond.


An auto trans always has some kind of 'positive' torque as it shifts from gear to gear (up or down). The clutch of a manual transmission allows a complete power disconnect. Add the centrifugal rotation to the lack of input torque, and you can see why the gears 'unmesh' slightly.
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Old November 14th, 2018, 08:01
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Re: AX-15 + NP-242, Revisited

lol yeah. i wish you the best there.

you won't find many guys trying to switch *to* a 242. most people are discarding them in favour of something reliable.
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Old November 14th, 2018, 08:27
Prefontaine Prefontaine is offline
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Re: AX-15 + NP-242, Revisited

Quote:
Originally Posted by cal View Post
lol yeah. i wish you the best there.

you won't find many guys trying to switch *to* a 242. most people are discarding them in favour of something reliable.
It's not as if the 242 is made of glass!

But thank you
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Old November 14th, 2018, 08:34
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Re: AX-15 + NP-242, Revisited

Interesting discussion.

I have considered building an AX-15/NP242 combo. Same reasons. DD in an environment with changing traction conditions.

I too would like to hear from those who have done it and have run it long enough to offer experienced feedback.
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Old November 14th, 2018, 10:13
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ehall ehall is offline
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Re: AX-15 + NP-242, Revisited

Quote:
Originally Posted by cal View Post
I believe he's talking about the (effective) spider gear assembly between the front and rear outputs. If you grab both tires on an open diff rig there's definitely a little slop between them.

IIRC only the front end is affected by it and it is a non issue. I'd be comfortable giving it a try without getting personal experience on the issue.
yeah that was my point. The only slop in the 242 is from chain stretch, same as on the 231. There's nothing about the differential itself, its just a bunch of gears.
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Old November 14th, 2018, 10:15
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Re: AX-15 + NP-242, Revisited

i'm not positive that i agree, but its not something i feel passionately about enough to go find one and prove it.
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Old November 14th, 2018, 10:20
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themauler themauler is online now
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AX-15 + NP-242, Revisited

My only feed back is this. AX15 paired with a Dana 300 4:1 and lunch box lockers front and rear.

You want to talk about slop in the drivetrain? There’s enough slop to almost throw me out of my seat by the time the lockers are 100% engaged again with the transmission. If years of that hasn’t touched my AX15 I think a 242 is safe.

Maybe the nay sayers have a stretched chain in their case making the problem seem worse but the way the 242 functions there should be no slop that gets back to the transmission output unless your rear axle is having problems or you have a lunch box locker


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Old November 14th, 2018, 14:41
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DutchVDub DutchVDub is offline
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Re: AX-15 + NP-242, Revisited

IMHO the reason the NP242 wasn't offered behind the AX15 is more of a options/money thing. Why put the "upgraded" t-case behind the base model transmission? There are plenty of AWD cars that utilize a center differential and have a manual transmission. I think you're over thinking it and I bet the reporting of it is fairly over exaggerated. I had an NP242 in an XJ (with an AW4) and it was great for winter driving on the road. I think an AX15/242 combo would be great for a stock or near stock daily driver. Of course like you, I've never done the swap so I'm just speculating. If you have the parts I say just do it. Keep your stock stuff so you can switch back if you don't like it. There isn't much to lose besides time.
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Old November 14th, 2018, 15:37
Jim Malcolm Jim Malcolm is offline
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Re: AX-15 + NP-242, Revisited

There is no center diff inside a NP242, what were they smoking. In every mode except Full Time 4WD, it is EXACTLY the same as a 231. Not the exact same parts mind you, but the EXACTLY the same function and functionality. There will be ABSOLUTELY no difference in 2WD or Part Time 4WD. None, zero, zip. I say this with 100% certainty.

The 242 adds a 1:1 planetary gear set to a 231, similar to the 2.72:1 planetary gear set that facilitates 4LO in both. The difference is, the 2.72:1 4LO gearset is between the input and output shafts. Is there excessive slop with a AX15 and a NP231 in 4LO? I didn't think so.

The 242 specific planetary gear set separates the rear output shaft from the front output shaft, unlike the 4LO gearset, which disconnects the input shaft (aka transmission) from the entire rest of the transfer case. The rear output shaft is solid between the input shaft and the driveshaft, solid. If it's in 2WD or 4LO, the rear output shaft is spinning. Period.

If there is any additional slop in a 242 vs a 231, it's between the front and rear output shafts, not the transmission. If there are any negative affects associated with a manual and a 242, they would be solely within the transfer case. So when is a manual really any different than an auto? When you're beating on it; quickly releasing the clutch between shifts, using engine braking to slow you down. Are you really going to be hammering on it while in Full Time? Don't answer that; I do and I love both my NP242s, including taking out a 231 to put one in. Long story short, the FT planetary has absolutely nothing to do with what the transmission "sees". It was "the last" "AWD" transfer case with a planetary gear set. Perhaps those people are mistaking it for the 241 found in the Grand Cherokees. The 242 is a completely different animal. It gets a bad rap because people don't know any better. You'll have to pry the 242 from my cold dead hands.
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Old November 14th, 2018, 16:12
Prefontaine Prefontaine is offline
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Re: AX-15 + NP-242, Revisited

Quote:
Originally Posted by DutchVDub View Post
IMHO the reason the NP242 wasn't offered behind the AX15 is more of a options/money thing. Why put the "upgraded" t-case behind the base model transmission? There are plenty of AWD cars that utilize a center differential and have a manual transmission. I think you're over thinking it and I bet the reporting of it is fairly over exaggerated. I had an NP242 in an XJ (with an AW4) and it was great for winter driving on the road. I think an AX15/242 combo would be great for a stock or near stock daily driver. Of course like you, I've never done the swap so I'm just speculating. If you have the parts I say just do it. Keep your stock stuff so you can switch back if you don't like it. There isn't much to lose besides time.
Thanks for that viewpoint. And I've enjoyed reading your build thread!

Quote:
Originally Posted by Jim Malcolm View Post
There is no center diff inside a NP242, what were they smoking. In every mode except Full Time 4WD, it is EXACTLY the same as a 231. Not the exact same parts mind you, but the EXACTLY the same function and functionality. There will be ABSOLUTELY no difference in 2WD or Part Time 4WD. None, zero, zip. I say this with 100% certainty.

The 242 adds a 1:1 planetary gear set to a 231, similar to the 2.72:1 planetary gear set that facilitates 4LO in both. The difference is, the 2.72:1 4LO gearset is between the input and output shafts. Is there excessive slop with a AX15 and a NP231 in 4LO? I didn't think so.

The 242 specific planetary gear set separates the rear output shaft from the front output shaft, unlike the 4LO gearset, which disconnects the input shaft (aka transmission) from the entire rest of the transfer case. The rear output shaft is solid between the input shaft and the driveshaft, solid. If it's in 2WD or 4LO, the rear output shaft is spinning. Period.

If there is any additional slop in a 242 vs a 231, it's between the front and rear output shafts, not the transmission. If there are any negative affects associated with a manual and a 242, they would be solely within the transfer case. So when is a manual really any different than an auto? When you're beating on it; quickly releasing the clutch between shifts, using engine braking to slow you down. Are you really going to be hammering on it while in Full Time? Don't answer that; I do and I love both my NP242s, including taking out a 231 to put one in. Long story short, the FT planetary has absolutely nothing to do with what the transmission "sees". It was "the last" "AWD" transfer case with a planetary gear set. Perhaps those people are mistaking it for the 241 found in the Grand Cherokees. The 242 is a completely different animal. It gets a bad rap because people don't know any better. You'll have to pry the 242 from my cold dead hands.
Jim, fantastic write up. Thank you for taking the time to submit that.

The swap is a go. I won't be doing it until December most likely, but I'll update this thread once complete. Hopefully when someone else is considering this years down the road, they'll find this thread and it can be the final authority on the matter.
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