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21 to 23 spline 242 conversion


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Does anyone know if a 21 spline NP 242 can be converted to 23 spline. Is all that is involved simply a matter of changing out the input gear from 21 spline to 23 spline. Also does anyone know if going from a 228 to a 242 is feasible since both are select trac. Any comments and input is appreciated. :help:

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A long time ago, in the early days of NAXJA, several people ran into problems trying to mix parts from various years of transfer case because the gear pitch was different from one year to another. That was, IIRC, dealing with NP231 cases, but it is possible the same situation might affect 242s. If you have the parts it might be wirth a try, but if you're shopping for a used box or parts, I would try to do some more research before plunking down any big chunks of cash.

 

The 228 was called "Select-Trac" because it offered a full-time 4WD position, but it's a totally different case than a 242 and I don't think a single part from one would fit the other.

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Thanks for your response. I have a 242 lined up on ebay. Problem is it is a 21 spline. However I have found a new old stock input gear for a 242 that is a 23 spline. If I open up the 242 and swap out the input gear with a new one that is 23 spline. Then in theory this should mate up with my 23 spline automatic transmission. The exisit 228 would be removed altogether and replaced with a 242. your thoughts?

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What year and what vehicle are we talking about? If you currently have a 228 transfer case, you must have either an '86 MJ or an '84 - '86 XJ. I thought ALL the AMC transfer cases in those years were 21-spline inputs. Are you sure the 228 is a 23-spline?

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A long time ago, in the early days of NAXJA, several people ran into problems trying to mix parts from various years of transfer case because the gear pitch was different from one year to another. That was, IIRC, dealing with NP231 cases, but it is possible the same situation might affect 242s. If you have the parts it might be wirth a try, but if you're shopping for a used box or parts, I would try to do some more research before plunking down any big chunks of cash.

 

I will second this. I had 4 231s apart and the input shaft varied in 3 of the units.

 

I would establish EXACTLY what spline you have (probably 21 spline) and get the TC you need. If it were up to me I would say get the 231 as I have seen more 242s fail than 231s and the 231 TC was spec'd far more often.

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