ok, 75w-140 isn't a heavier oil, it has a different protection range...
ford 75w-140 is made for ford rear diff's with limited slip, and is made so it never needs to be changed unless it is submerged in water (this is only if it is in the differential it was made for, i'm not insinuating that it needs not be changed in our diffs) but i woudln't recomend it....it is made for those diffs and not ours
some gmc diffs also take a form of 75w-140 but with a slightly different additive package, although both oils do come premixed and aren't just an additive bottle....
speaking of additive bottles, all 3 major companies offer one (gm, ford, dodge) and they all contain a slightly different package formulated for the differentials in those specific cars, again, not recommended our ours imo
the best oil for our diffs would be a 75w-90 gl5 synthetic gear oil, however using synthetic in mine seemed to make it seep (not even leak as the level doesn't go down but the case IS slightly damp)
the oil for the tranny should be 75w-90 gl4 gear oil (synthetic is again, fine) but should be of the gl4 variety....gl4 has been surpased by gl5 but does have some applications which are not superceded, some toyota transmissions being those applications
hence, i woudln't recommend using gl5 in our tranny's, even though it *should* work, i think it was something to do with the syncro's not liking it or something to that effect
regardless, that is the oils we should be using, and using ATF or something crazy like that is just retarded, unless you are looking to ruin ur tranny, but if u wanna do that good ol' h20 might help lol
so:
tranny: 75w-90 gl4 (synthetic or no)
diff: 75w-90 gl5 (synthetic or no, don't matter here either, but make sure it has the lsd additive package (very common for synthetics, conventional doesn't always contain this))
*phew*
lol
thats all i know, if someone has another opinion or idea pipe up cuz this is just what i've heard from reading on the net and working at a lube shop and investigating this very thing....
thanks
