I have a Dodge Avenger that has a nice hole in the bell housing from where parts of the differential went through it. I have another tranny that makes a bit of noise so I was going to take the diff and bell housing from one, and put it on the other, replacing all the diff bearings. I was reading in the factory service manual that you have to preload the bearings which involves taking the gears out etc etc and was wondering if this was absolutely neccesary or if people had swapped them out without checking the preload and been fine?

I have no problem tearing the whole thing apart but it seems like a PITA and if I can skip it, that would be preferable.

Thanks in advance.

I never bother. It makes the trans a little noisey, but i never saw undue wear and tear from it.