231 to 242 Xfer Case Swap Question

I've got a NP242 from a 93 ZJ I'd like to rebuild and swap into my 89 MJ behind the 1998 AW4. Based on the guides for snout length and spline count (23), I'm pretty sure it will bolt up. I have two questions though.


1. How do I determine if I should replace the chain?


2. The 242 has the boss where the vac disco switch goes, but it doesn't go through and isn't threaded. Do I drill and tap it, or do I swap over the tailcone from the 231?



3. Will I have problems shifting in/out of 4wd with a vac disconnect front axle? I've read conflicting info on whether the 242 has a synchro like the 231s did.





Current 231J Xfer Case:
p/n 53006093
ser/date 6 22 89 1


Donor 242J Xfer Case

p/n 53009359
ser/date 10 28 92 2

edit--89 and 93 should be the same depth but different spline counts -- RENIX was 21 and HO was 23

1) If there's wear on the case internal it needs replacing. Otherwise try to line up the main shaft for the oil pump and get everything in place without reseating the halves, and look at the droop.

2) RENIX with the 242 did not have the vac disco, instead had one-piece shafts. You would need the vac disco work in FT, otherwise all the power would go to the open two-piece shaft (no resistance on that side of the axle diff, and almost no resistance on the front output of the 242 diff, so all the energy goes to the front and then to the open joint). Probably easiest to just rig up a cable and activate when needed, if you don't want to go to one-piece entirely.

3) 242 has a synchro on the internal diff to help it engage AWD/4WD. But if the half shaft is unloaded it is going to spin like crazy and the synchro won't help.

Thanks. I was suspecting the easy answer was to rig up a manual activation of the disco using either the aftermarket cable kit or maybe grab the manual vac switch from a wagoneer. I could also do the mod with some all-thread and a few nuts to permanently connect the disco.



Sounds like I need to split the case and see what the chain looks like. I measured about 3-degrees of play between the rear and front outputs. I'm thinking it's probably fine and will just order the master rebuild kit for now and wait to see if I really need to spend another $100 on a chain.

Be careful what kit you buy. There was a noticeable difference between the input and front output bearings in the Transparts BK242B kit I got and the Timken bearings and seals I replaced them with. Doing it again, I'd piece together a kit if I could find the shift fork pads.

Jim Malcolm said:

Doing it again, I'd piece together a kit if I could find the shift fork pads.

Click to expand...

The shift fork pads are readily available.......
https://www.quadratec.com/products/52219_0003.htm

OP: You have to check the chain slack thru the drain/fill plugs, once you split the case, the bearings are no longer supported. If you get to split the case then a visual should tell you whether you need new parts.

Just in case you didn't see the correction above, 89 and 93 should be the same depth but different spline counts -- RENIX was 21 and HO was 23

ehall said:

Just in case you didn't see the correction above, 89 and 93 should be the same depth but different spline counts -- RENIX was 21 and HO was 23

Click to expand...

The MJ started life with the AX15, which was always 23-spline. I transplanted the 98 AW4 quite a few years ago. So both xfer cases are 23-spline short, and the AW4 is 23-spline medium. Should bolt right up. I am assuming though that the 242 from the ZJ is clocked the same.

: You have to check the chain slack thru the drain/fill plugs[/QUOTE/


That's what I was wondering -whether there was easy way to check the chain stretch before I order parts and start tearing into it. You'd think there would be some spec like x-number of degrees play in the front sprocket. I'll probably just order the chain instead of wondering.

Click to expand...