If I was to use Amsoil synthetic rear diff lube in my 02 f350 with limited slip, do I need to still add the friction modifier, or not?

I will let the Oilman answer this question!

But, (this is just what I have heard); Ams Oil has the modifier in the fluid and is cheaper. That is just what I heard and is not a fact on my part.

First, the AMSOIL "Corporate" answer, taken straight off the product data sheet: "AMSOIL Severe Gear is compatable with most limited slip differentials. If limited slip differential chatter occurs, add AMSOIL Slip-Lock friction modifier additive."

My personal experience. Dodges - always add the extra additive, the Dodge 3500 needs 2 bottles. Fords and Chevys over half the time do not need the additive, but it can't hurt to use it.

Remember with all types of limited slip differentials, any time you do anything on them, even just a differential oil change, ALWAYS do a run-in - take the vehicle to a large open parking lot or field and do half a dozen slow figure 8s. Even with additive most will chatter the first several turns. If you don't put in the additive and it chatters at the end of the run in, you need it.

If you would like a copy of the data sheet, send me your e-mail address and I will send it back - pdf attachment.

Don I want to thank you for sponsoring the Automotive forum. It only seems right that your here with us!

One can purchase all the products Don talks about also on his website at a decent price. Don is good enough to help us all out so hopefully some will take advantage of his online store.

http://www.the-oilman.com/fishingminnesota/

Ya, Don!

I know the manufacture of some vehicles (under warranty) can throw us regular Joe’s a loop holes on synthetics, but I have been an Ams Oil backer since high school. Anything I run synthetic has Ams Oil in it and it helps for starting in cold conditions and much more.

Thanks dude for the info!