Ive got a '89 2wd f150 with an 8.8" diff that I want to change the diff oil in soon. What oil is everyone here running?
My haynes manual only says hypoid gear oil. If I use hypoid gear oil do I still need to put the LSD additive in?

thanks

 

I'm using Amsoil 75W-90 synthetic with Motorcraft additive. It's about time for me to change it again.

Some gears oils say you don't have to use the additive, but I always have. Maybe someone can chime in on that...

 

Ok, thanks. I think ill put the additive in, the cost of the additive doesnt worry me as much as damaging the diff.
What weight does ford recommend for these diffs? is it the 75w-90?

 

You only need the additive if you have an LSD, not using it may only make the clutches chatter a little under certain conditions and even then only if the clutches are not worn, on a high milage truck you likely won't notice any difference.

 

80w90 weight gear oil is the spec. Using conventional instead of synthetic might not be the worst idea if the seals on your axle are original. Synthetic oil may leak around older seals easier. As already said, the additive isn't needed unless you have a limited slip.

 

Ok, cheers. I spoke to a dealership here and they said they would put in what castrol recommend which is castrol axle limited slip 90, checking with castrol they say no additive is required with that fluid as it is already in there.
Ford Australia were of absolutely no help at all to the point of being rude and telling me that my truck was obsolete.

 

Don't be afraid of 85-140 either, especially if working the truck hard.