ok heres what i already know
- np231J is pretty common on cherokees fairly week and can accept 21 or 23 splines
-np231C is common on 4.3L chevy gm blazers, 6 gear planitary and wider chain and 26 splines, internals can be swaped to a np231J for more strenght
-np231HD on 2nd gen ram 1500 pickups(ok thats all i know on this 1) its used on a larger truck with much more powerful engine would assume its even more beefyr? can internals be swaped between the other 2?

also what are the bolt pattern options for these? are they the same?

 

the one im most intersted in learning about right now is the np231HD

 

im pretty sure theyre all different bolt patterns. the wide chain from the chevy is a nice upgrade, if you need it. plenty of dudes running strokers with stock 231s with only a SYE added. i wouldnt even bother looking into the 231HD- you dont need anything else, the 4.0s are anemic when you compare them to any modern V8 and the 231 is plenty strong.

i looked into creating a 242HD, with 4:1 low a while ago, just so i could keep the fulltime and have the beef. it required a custom teralow kit (that tera used to make) and parts from H1 and MB tcases. sure, it would be a 2wd,4 part time, 4 full time, and 4:1 low that could handle 400ish HP and 600ish lb/ft of torque, but in the end, its still a chain driven, thin aluminum casing tcase.

 

[QUOTE=93XJLI;2035591]im pretty sure theyre all different bolt patterns. the wide chain from the chevy is a nice upgrade, if you need it. plenty of dudes running strokers with stock 231s with only a SYE added. i wouldnt even bother looking into the 231HD- you dont need anything else, the 4.0s are anemic when you compare them to any modern V8 and the 231 is plenty strong.QUOTE]

Think about an auto verse manual, an auto will apply smoother torque curves to the case then a manual will.
You also have to consider where the torque is being multiplied. If you are running stock gears in your axles, or gears that arent low enough to compensate your tire size; then your furthest rear case (because we were talking about doublers the other day) is where most of the strain is. You will be more likely to shatter the case or twist the driveline. Your gears and axle shafts are not the weak links.
Once you gear your axles, the t case and driveline are now safe but you better make sure your gears are set up properly, you have a thick diff cover to reduce deflection, and you should be running chromoly shafts.
If you went the other direction and left your diff gears stock, t case in high range, and you were running an auto under a leavy load (when you should probably be in at least 4 low); then the torque is mostly being multiplied by your torque converter. Your t case, driveline, and axle assembly should be safe but now you have to worry about over working your torque converter and heating it up.

Its all a matter of wear you have positioned the weakest link. Which is also why in a doubler situation, they tell you to never run the front case in low and the rear case in high. Make sense?

 

ya been thinking about it, i think leaving stock gears in both t-cases is the way to go and will get me everything i need, im interested in my dodges t-case (either regular 231 or the 231HD ) mostly for the chain (and mabey other weak links in my current t-case).im interested in this because i already have it lying around.

i was considering when making a crossmember for the second t-case having it travel over and under (prob add a skid to wile im at it) sorta to make a brace... correct me if im wrong if this isnt the thing to do to help it..

also realizing i prob will have to lower my diffs a bit, i think what i have now is 3.54:1, i havnt looked into it yet but i think 4.1:1 is a common one that could probly lower it enough,,, with this i think there will be less toying with my trany (ax15) gears, but it itself will need some beefing(trany)

and both front and rear axles will be built up