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Some tranny/t-case interchange questions (AW4, BA-10, 242)

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OK, so I've got a few questions for you guys.


First off I've been trying to find out if a the output shaft on a BA-10/5 is the same length as an AW4. I know it's 21 spline but not if it's the same length. Reason I ask is we recently bought an XJ with a BA-10/5 and 231 and we'd like to swap in a 242 if possible.


Second question, is there any way to tell, short of actually taking it out and counting the splines, whether an AW4 is 21 or 23 spline? Any known difference in casting or part numbers on the tranny or t-case? I had always heard that the change was for the '91 model year, but just read in another thread here that it was actually mid year '90. This seems entirely logical to me as we currently have 2 '90 XJ's and you can actually see how things were gradually changing during that model year. Both have the c-clip rear, but one has the old style front hubs/brakes and the other has the newer style. A while back I smashed my 23 spline NP242 in the MJ on a rock and had to replace it with a 231 because I assumed the 2 spares we have ('89 and '90) were 21 spline. I really miss the 242 in the MJ for winter driving and it would be sweet if the '90 was in fact a 23 slpine, but I'm not gonna yank it out in my driveway in the snow just to count the splines.

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I don't think you'll have any length issues. AFAIK, there's only two input lengths.. and the long input was only used behind the AX-4/5.


If all else fails, the input shafts between the 242 and 231 are interchangeable. So even if you have 2 21 spline 242s, you can put a 23 spline 231 input in it.

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The AX-4 and AX-5 are identical, aside from some separate internal parts that give the AX-5 the fifth gear. These go behind the 2.5L 4cyl, 2.8L V6, and 2.1L Turbo diesel. These CANNOT go behind a 4.0. Even if you had a custom bellhousing made, the transmission would not last.


The AX-15 can go in place of the BA 10/5 fairly easily. There are several threads listing everything that needs to be done.

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