Originally Posted by
trf211
If you are referencing the b74 alu f/r diffs, I noticed they help prevent the diff cup side outdrive from leaking as much or at all. The alu center diff will reduce spur gear damage due to the AE spur and diff sometimes being a little off true. The plastic center cases do not seem to have a leak issue in my experience.
I'm just adding these benefits to the list of already mentioned oil cooling. They might have just a smidge more oil capacity due to the slightly different inner design but it looks really close.
I was very happy once i got the RD aluminum diff cups f/r and center. Everything runs true, no oil leaks, o-rings are not worn out nearly as fast thanks to the slot for the o-ring actually concentric to the outdrive shaft, no more annoying drivetrain vibrations that was hell on the car causing it to prematurely wear out "clap out", constant diff action from the start to end of runs, and finally the spur and gear mesh was no also concentric cutting the wear down.