Well, shifting the txfr case seemed a little stiff, so I checked the fluid. It wasn’t dry, but it took over a pint to get it full.

While I was under it, I noticed the seam between the trans & txfr was wet and appears to have been leaking for a while. The trans checks full, so the txfr case it is.

I know it has to be dropped to change the front seal, but before I do that, I was considering going to a lightweight gear oil & see if that would slow it down.

Now a question; I read online that most transmission fluid is in the range of 0 to maybe 10 weight on the “SAE AUTO” viscosity scale (where motor oil is weight rated). I also see on the “SAE GEAR” viscosity scale that 75 weight overlaps with 10, 15, and the low end of 20 weight of the SAE auto vis scale. Seems I could run straight 75 or 80 weight gear oil if available?

 

https://naxja.org/threads/motor-oil-...-case.1135061/

 

I use Mobil 1 synthetic 5w-30 extended performance in my transfer case, since I already have it handy for use in another car.

 

I’m going to try some non-detergent or at least low detergent motor oil and maybe just single weight oil if I can find it. I’ve read dozens of replies to questions, posts, ads, stories, etc that say NOT to use motor oil in gearboxes. I know the NP231 is not much of a gearbox, but there are a few gears, a chain, and sprockets in there. Most all advice on the inter-webs say multi-grade motor oil with coil-up molecules won’t hold up if constantly running in gears and the carbon buildup prevention additives will cause foaming if motor oil is constantly stirred / agitated. Seems single weight gear oil just slightly heavier viscosity than ATF would be perfect. I’ll try out the 5w30 & see how it works….