I'm going around checking fluids for tomorrows trip and I was a little low in the transfer case. I have been putting in Coastal 80W-90 but ran out. I was at Adv. Auto and couldn't find the correct weight in that brand so I got Valvoline 80W-90 (it does say "limited slip"). It shouldn't matter too much...right?

Thanks.

Yup you're fine. You could mix just about anything in there (except, maybe, vegetable oil) and be OK as long as you remained relatively close to the original spec weight. Lots of people actually run 50w oil in the t-case and this is what Ford suggested during the earlier years of the Bronco.

I think Ford changed over to an 80-90 reccomendation sometime around 1974. I had thought it was closer to 1971, but could be wrong about that date. My understanding of the conventional wisdom it is that the 80-90w gives a little more protection and the 50w gives a little better mileage.

I dunno. All the stuff I've read talks about SAE 50w non-detergent, which would limit you to just the racing oils. I've always just used gear oil and called it done, so I haven't looked into it much beyond what I've said above. I could definitely be wrong about that. The notion of using something that light made me nervous, especially since the Dana 20 wasn't really designed with 35" tires in mind.

It doesn't take much to lube the D20. I rebuilt one that was run with auto trans fluid in it and it was in good condition. Really clean inside too. I still don't recommend it though. Impossible to keep it from leaking.