Driving in reverse hurt the diff??
 

This is probably a really weird question... but I was wondering if anyone knew if driving in reverse for extended periods of time can do damage to the differential?
I was thinking that the internal gears work better if spinning in the one direction than the other or something.
Any help would be greatly appreciated.
Thanks :)

I think you'll be fine if you don't overdo it on power. The pinion bearing loads could be a problem if the loading is heavy as the thrust will be on the smaller pinion bearing in reverse, but it can't be that big a deal since there are both high and low pinion 4x4 front axles. A low pinion front 4x4 axle is essentially in reverse whenever it's driving the front wheels. I don't know if the gear tooth profile is reversed in a low pinion 4x4 front axle, but I imagine it could/would/should be reversed.

Why do you ask?

Im building a custom tube frame 4x4 that I would like to use independent suspension all the way around on, but I am having a hard time locating front and rear differentials for independent suspension that have the same gear ratios and limited slip... so i was think aboot using rx7 ones cause i have a few laying around.
Unless someone else knows of anythink that has such a suspension that i could make work with a transfer case :)

I'd use 4.10 geared Datsun/Nissan IFS with a 4.10 Mazda rear. The R180 Nissan differentials are quite strong. If your 4x4 is light and doesn't have to huge of tires it should be fine.