I ordered a 3.6 Torsen from the UK. FedEx was nice enough to drop it and booger up the companion flange. No biggie, I have an old 1.8t open diff laying around that I will get a flange from. Since I am opening it up, I am debating on swapping the 3.6 ring and pipnion into my open housing since the 3.6 housing is rusted to crap. Should I be worried about the rust or just use the 3.6 housing as-is? After everything I am spending to build my hopefully 300whp engine while upgrading to 6speed and 3.6 I would hate to damage the 3.6 die to weak housing.

 

 

 

That amount of rust looks not untypical for a diff that's seen lots of winters with salt on the road. I'd wire-brush the worst of it off to see if it's any more than a crusty surface coating, and if it's okay just use that case to save swapping the pinion over.. A couple of the fins look bad but will probably turn out to be less dramatic when cleaned up. UK MX-5s often have diffs which look like that but the cast steel cases are never the part that breaks.

 

It's thick, cast steel. Just wire brush it, hit it with some rust converter, and then paint it.

 

That's nothing. I've seen cases with the fins nearly gone. Cleaned up (bead blasted) just fine, and has been holding up to autox for years.