I’d like to change of my gear oil in my 60’s era differential and I am looking for feedback on doing it. It’s low mileage (for a 50 year old vehicle), only around 43k. Even though I’ve owned it for the last 25 years and 20,000 miles, I don’t think it has ever been changed. My question is, should I pull the axles and the 3rd member and really get all the gunk out, or will it suffice to try and suck as much as I can through the fill plug and just refill it with fresh gear oil? I think I know the answer, but thought I’d put the question out there anyways. I guess I really am unsure how much sludge is likely to be in the bottom, so that’s my dilemma.

 

Suck it out, refill, drive for a month, do it again.

Serving suggestion.

Unless you got water in there at some point, it's probably not as bad as you imagine.

Maybe.

 

Thanks for the opinion and idea. I suppose I could try it, because I do have some dino gear oil that I can use the first time around. I plan on using some synthetic gear oil in the end. It may be harder to remove the old stuff than envision.