rear diff fluid(what to use)

[sharkdog]

Just wondering what gear lube I should use in my rear end I checked my owners manual and it just has the ford part number and calls it hypiod gear lube. I saw somewhere on the internet I think that it's basically 80w-90 , is this correct? Also i'm kinda a mobil 1guy and there gear oil seems to be a 75w-90 just wondering if that would be ok and if theres any issues with it being a synthetic synthetic. I don't know what rear end I have but my truck is a 70 f-100 2wd with a 360/c6 it has the heavy duty springs though i'm guessing that makes little difference. I know it Definitely does not have any kinda of posi/lsd(do to a quick trip around my friends barn and getting stuck/sinking into the wet grass) so i'm assuming I don't need any kinda of additive with the gear oil.

Thanks Pete

[tbone6]

I have been using Royal Purple Max-Gear 75W90 for awhile now. Seems to do the job.

[Red Mercury]

I use Shell 80W90 and have not had any problems getting the diff to last 250,000 miles. Really I don't think it matters what your brand is as long as it is a heavier gear oil. There won't be much difference between 75W90 and 80W90. Synthetic is up to you--I don't bother with it. More importantly than the brand is that the oil gets changed periodically and the diff doesn't run low on oil. I have seen some worn out diffs with filthy black oil in them which may have never been changed.

[sharkdog]

thanks for the reply's