I have an 87 745 that I am considering converting to manual transmission. Obviously, the 4.10 rear axle will have to be replaced with a 3.31. My question is, what year(s) of axle can I use, and more specifically, can I use one from an 89?

From what I understand, cars up to and including 88 have a 12 tooth tone ring if they don't have ABS, and 96 teeth if they do. 89 and later have 48 teeth on the ABS cars, but still are 12 on those without, though all the part numbers for the axle internals are different. The 88 and older have a steel differential cover, 89 and up a cast aluminum one that takes a different type speed sensor, so I guess the real issue is, is the 89 speed sensor compatible with the 87 speedometer?

The reason I am asking all this is that I have located a 3.31 axle in an 89, for a good price, and 88 and older 3.31s seem to be VERY hard to find.

Any definitive information (from someone who has done such a swap) will be much appreciated.