bigjimslade wrote:
tjkj2002 wrote:
Non-syn is best for your diffs,if you do not tow or wheel it heavily the cheap 80w-90 gear oil is best,if you do two and wheel it 85w-140 for the rear is best.Skip the syn stuff unless you change it every 15k or just don't like your diffs at all.You can do both diffs with non-syn for about the price of 1qt of syn gear oil.
T-case is ATF+4 regardless of which t-case you have in a KJ.
Some tough winter snow

and maybe towing a small boat or trailer it about all for me (only occasionally). I don't really do any hard core wheeling.
I guess I would ask what does synthetic do that is bad? I thought I had read previously that you used royal purple synthetic...maybe I'm confused with someone else.
I did at one point and after 10k my axles and bearings had a nice sludge coating on them.After that I only used Lucas 85w-140 non-syn,diff ran cooler(gears themselfs),and generally a smoother ride.
Syn gear oil is only used for mpg's but does not have any advantage over dino gear oil in protection of the diff.You don't want a "better poor rate" for gear oil,you want it thick and sticky since there is no pump to lube the diff.