Just finished engine oil change and gear oil in the rear diff @310K. Got a 16 hour drive coming up soon.

Truck is RWD 9.25 corporate rear axle, open diff. Used Supertech full syn 75W90. The oil I removed had 56.5K on it and it was honey color. The magnet had barely any build up, a light dusting caked on. After removing the bolts, I had a really hard time breaking the seal to get the cover off. It laughed at my rubber mallet. I put the floor jack so it barely caught the lip of the diff cover, then jacked it up to break the seal. That resulted in a floor full of gear oil though. What a mess.

I realized it wasn't worth pulling the diff cover and having to deal with scraping the seal off mating surfaces, etc. The oil stays clean with an open diff. Next time I'll just stick one of those hand pumps down the fill hole and pump it out.

 

We drained the gear oil from the dragster last week. 70-odd runs making sub-1 second short times and absorbing 2000+ HP, and it and the gears looked brand new.

 

I wished they would put drain plugs on the diff. Covers. But you get to inspect everything with the cover off.

 

That would make sense, right? They do sell the covers with drain plugs (aftermarket), but I don't do this enough to justify the expense. Being that the open diff has no clutches, I think I'll be fine with just pumping it out next few times at least.

 

I just had the cover off my 91 D150, it was off once before but I think just once lol. Fluid was black, had a slight burnt smell to it, and like you stated being an open diff. There wasn't really any gunk, or debris on the bottom of the housing. I put a little bit of Lucas in, and refilled with 80/90 gear oil. I bought a locker to install, but little did I know it has the 8.25, not a 9.25 (assumption is the mother of all fudgeups) so now I'm looking for a 9.25 so I can put this locker in, I would send it back and exchange it for the 8.25 but I don't think it'll hold up to my 360 build for very long. Not sure I need the locker though it'll actually spin both rears on an open diff.(in dirt) Lol. I had to put a wheel stud on the driver side anyways, so I pulled the driver axle shaft while I had the cover off, and I put a spring and adjuster kit on the new shoes that the PO put in.