Found a pretty good comparison of gear lubes, while it may only be 75-90 and 80-90, and does not include 75-140 I think that conclusions can still be drawn, and lots of interesting information is in the study. If you are into reading college thesis style studies it is great, if not you might just grab your insurance policy for a good read, or skip to the end and look at the last chart...

http://www.lastgreatroadtrip.com/wp-...comparison.pdf

 

Cool find! Paid for and conducted by Amsoil...but it actually seems legit. I wish they'd brought Schaeffer Oil to the party, but there's probably a few good reasons they didn't. Been running that in my diffs for 10 years, totally happy with it. I love their greases too, worth the price if you ask me. Especially if you forget to hit the zerks on occasion, like me.

So does this info change what gear oil you run?

 

Kind of, I missed that it was paid for by amsoil. Makes sense, but hey good info on the rest of the lubes. I was surprised schaffers wasnt in there as well, but it all makes sense. You cant upstage your own oil!
Kind of it changes my feelings slightly, and i wish I would have seen this 3 months ago when I changed my rear diff , tcase and tranny to royal purple from the lucas I had been running in them, but thus is life, I am slighly discouraged that despite what I thought, I did not get the absolute best fluid, I am running full synthetic fluids throughout and I know they will be just fine without it. I also end up changing my fluid more frequently than recommended anyway so whooptie doo. The next time I change my rear diff fluid in probably 5 years(20k miles) I will probably go to mobil, but i really am beginning to like them more and more, both my care and my wifes run their oil, and i only buy from the mobil station. The fluids have always done well by me. whatever. The biggest irritant is that i could have saved $7 a quart going to mobil over royal purple. Oh well live and learn. I do feel vetter that the rp is a slight step up from the lucas I was running, and that is a step up from the long overdue dino oil that was originally in my rear diff...

 

Me thinks that may be connected, jk i have no idea. Ill say this though, after talking to machine shops, engine builders, trans builders, rear-end builders, car builders, hot rodders etc. Royal Purple and Lucas are always the recommended oils, i cant think of a single time that Amsoil has been recommended that wasnt by someone selling it.

 

You have a really good point with that whole "unless they were selling it"
It still makes me feel warm and fuzzy inside knowing i am running full synthetic fluids, and the diva inside of me loves the fact that all my fluids colors match! pink coolant, purple tranny fluid, purple tcase and purple rear diff! They dont taste similar though!

 

I need to open the diff on my Explorer to check it out and was bummed I'd be loosing the high dollar Royal Purple, now I'm motivated to open it up. Thanks!