LSD oil question

[The Bloody Panda]

I've got a Cusco RS 2way LSD in my 86 and almost 200hp. I've previously been running 80w-90 for my LSD gear oil but I'm about to do a fluid change and after talking to Cusco they're suggesting that I run their 80w-140 gear oil this time. I'm a little concerned about how it will affect my performance. Anybody have any experience with switching from 80w-90 to 80w-140 and the perceived difference?

[gotzoom?]

The numbers refer to the temperature range that the oil is designed to operate at. Higher numbers mean higher temperature. The ring & pinion do generate quite a bit of heat, so if you drive hard, you'll have more protection at high temps with the heavier oil. The ring gear and most of the diff sits in the gear oil at all times, so you don't really need to worry about cold start wear.

[Deuce Cam]

A higher viscosity oil is good idea for an aftermarket lsd such as cusco. My cusco rs 1.5 was insanely loud (i.e. clunks) on motul 90pa, and adding motorcraft friction modifier didn't help much. Over time I've noticed that the clunks become more frequent on longer drives - I'm assuming since more heat. I've since switched to convential valvoline 85w-140 with 1 bottle of motorcraft friction modifier and noticed smoother engagement and less clunks.

I've always wanted to try the 80w-140 cusco oil but haven't been able to justify the price at $40/qt. I kind of regret not using from the start because I bought the lsd brand new. Cusco also makes a 80w-90 for 1 way lsd's, but they recommend the 80w-140 on 1.5 and 2 way units.

[The Bloody Panda]

I went ahead and bought the Cusco 80w-140. I ran Redline 80w-90 in my diff briefly and was not impressed, I ran Cusco 80w-90 for a time and had no complaints what so ever, have recently been running Amsoil 80w-90 and am satisfied with it other than that it doesn't quite feel as nice as the 80w-90 from Cusco. So I guess I'll be seeing how I like Cusco 80w-140, I'm betting that it's going to be nice.