SYE vs Fixed Yoke spline geometry

[OptionXIII]

Basically the title. Does anyone have detailed information, such as a dimensioned drawing, of how spline geometries differ between fixed yoke and slip yoke splines, specifically for 32 spline outputs?

The context is I'm working to piece together an NP242HD to fit in my XJ. I'm using a HMMWV rear bearing housing to get a speedometer output, and I am considering using an HMMWV main rear output shaft as well. This would give me a shorter rear output yoke than the IRO 32 spline hack n tap kit with the WJ HD rear output. Plus, the HMMWV shaft is already cut for the speedometer drive gear snap rings, unlike the WJ HD main shaft.

I tried swapping the 32 spline 242J front output onto the 32 spline WJ HD rear output and it would not go on. It goes on the front output of the HD case just fine. Is it just a difference in the major OD of the shaft, or the minor ID of the fixed front output yoke? Or are the splines themselves of such different geometry that one cannot be adapted to the other?

I have access to a machine shop for some work, but I need to provide my guy some guidance rather than just grunting and saying make it work.

Ideally I'd like to find a cheap and short output yoke (such as off another '96+ 242J) in the junkyard that works, and get a custom seal retainer made (my guy with the machine shop works for beer and materials cost). That'd be a lot less spendy than having to modify a $200 IRO kit.

This case is well beyond my needs, but I'll be putting it behind a manual transmission so the extra torque capacity will be nice in case of accidental clutch drops, and I like to have rare parts on my XJ.

 

[phissure]

I have no information to offer, but do have a question. Why the NP242 instead of the NP231? I'm new to XJs and am curious.

 

[Da XJ nut]

I got my NP242 out of a 97 ZJ with an auto and 4.0 like my 97 XJ. My XJ is a converted 4x4 with the front axle also coming from the ZJ due to it being the same gear ratio as my 8.25 rear axle. the t/c is 27 spline output with 23 spline input like almost ever Jeep XJ from 94 up to my knowledge, I just know the earlier years only had 21 spline input

 

[Rob Mayercik]

I have no information to offer, but do have a question. Why the NP242 instead of the NP231? I'm new to XJs and am curious.

The NP231 (also known as "Command-Trac") offers 4 options - high-range 2WD, high-range 4WD, neutral, and low-range 4WD. The two 4WD options with this case cannot be used on dry/high-traction surfaces because the front and rear outputs of the transfer case are locked together. Operating the vehicle in these "part-time" modes (especially turning since that requires the front and rear wheels to turn at different speeds) build up in the drivetrain; without wheel slip to relieve that buildup, you can suffer a catastrophic failure somewhere in the drivetrain.

The NP242 (also known as "Selec-Trac") has all the options of the NP231, but adds offers a full-time 4x4 option in high range. This is achieved with a differential inside the case between the front and rear outputs. In 4Hi and 4Lo this differential is disabled, locking the two outputs together, and imposing the same limitations as I noted above for 4Hi and 4Lo in the NP231.

In the "4 Full Time" mode, however, that differential is enabled (unlocked), allowing the two outputs to rotate at different speeds. This allows the "4 Full Time" option to be usable under any conditions and is essentially "all wheel drive".

The 231 was the "standard" transfer case in the XJs while the 242 was the "optional upgrade", making it by default slightly rarer. As the O/P noted, he likes rare parts - I wonder if he's on the hunt for the elusive hidden winch kit?

(The middle digit in those model numbers, by the way, indicates the relative strength or possibly torque capacity of the units. Based on that, the 242 is technically a little stronger than the 231, but I don't believe the strength difference is actually significant)


Rob

 

[Evan03]

Seems the cheapest easiest option is the hardest for you to grasp.

Modify the 200 dollar parts and move on

Sent from my SM-G781U using Tapatalk

 

[OptionXIII]

Thank you for the condescension Evan! I appreciate you for coming down to my level to share your wealth of knowledge. I would have been lost without you and I'm sorry I wasted your time.

With respect to the other comments:

For the hidden winch, I wanted a Boostwerks Comp Mount but they went out of production just in time for me to commit to the idea. I ended up cutting up a steering brace and combining it with a front hitch. I'll get a hitch mount winch setup to match. I didn't really want to carry around that much extra weight all the time anyways, so I'm happy with how it worked out.

I like the all road, all weather traction a 242 offers. Does it make things more complicated for SYEs? Yes. I'm okay with that. This is not my highest priority project or I would just go with the instant gratification, higher purchase price option that Evan so enthusiastically endorses. I was probably going to do that anyways, but I do like to better understand things rather than just pay someone else to.

 

[Rob Mayercik]

For the hidden winch, I wanted a Boostwerks Comp Mount but they went out of production just in time for me to commit to the idea. I ended up cutting up a steering brace and combining it with a front hitch. I'll get a hitch mount winch setup to match. I didn't really want to carry around that much extra weight all the time anyways, so I'm happy with how it worked out.

I hear you on the extra weight thing, which is why my winch is on a cradle that I can just throw in the receiver in my front bumper when I hit the trails, and leave it either in the garage or strapped to the spare tire in the back otherwise.

If you haven't already decided to (or if it doesn't already come with it), I highly recommend equipping your winch with synthetic rope as part of setting up the hitch/cradle mount, it'll save your back more than a little. The 100 feet of 3/8 cable that came on my winch must have weighed close to 40lbs, but the 100 feet of 3/8 rope (with thimble) that replaced it weighs all of 6lbs. The hitch mount itself adds at least 20lbs - I think my setup is around 50-60, but it would have been in the 80-100 range with the cable.

 

[RCP Phx]

Have measured anything yet, there is a common standard for shaft splines. There is also a +/- tolerance for slip fit or press fit splines/yokes.