what fluid to use with Torsen?
 

I swapped my open diff for a torsen. The manual calls for 80w90 for my open diff. My Mustang w torsen calls for 75w140

what should I be using

Returd, the Toyota Torsen LSD does not take any special gear oil. The same 80w-90 or 75w-90 weight oil is what is used. Mobil1 synthetic gear oil is a good easy option. I also like Redline Heavy Shockproof gear oil in that weight which is what I am using now. What you do not want is any gear oil that has a "friction modifier" additive. Since you have a 100% gear based LSD and not clutch packs that would be unnecessary and counter productive to the function of the Torsen's gears.

A Toyota Supra/Soarer Torsen LSD needs regular oil changes every 30k miles, pretty much the same as the open diffs.

Your Mustang has a newer Torsen LSD design but it's not that different (93-98 USA/Export Supras were equipped with T-1's and I think the new Mustangs use T2's or T2-R's. Interestingly late model Soarers and other JDM performance JZ Toyotas eventually got Torsen T2's).

Ford had some reason for specifying 75w-140 so that is what should be used for that car's rear diff. For the 200mm SC/Soarer/MKIV application with a Torsen T-1 we stick with the oil weights above which are identical to what the open diffs call for.

Thanks Kahn

I suspect Ford spec's the 75-140 because the pumpkin is aluminum and heats up more. My mustang is a T2r btw.

I'll likely pick up a few liters of Amsoil 75-90 tomorrow.

I wish I would have seen the Ford conversion before doing the Supra/SC torsen conversion. I have four Ford diffs.