489 vs 742

BigBlockMopar said

The 489 has a thicker pinion, but all the 3 types all neck down to the same size near the splines.
And when they break, the bearings caps and ring gear teeth are the first to go. Usually not the pinion.

You think you're making enough power to break one?

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There's one exception to the rule that they all neck down to the same size. Fine splined pinions used in later 489's are a larger diameter than coarse splines. But I agree that's not where they usually break first anyway. I usually see the ring gear teeth go first.