How much friction modifier when changing LS diff oil?
 

okay guys im going to use the royal purple 75w/140 that supposedly has the friction modifier in it, but i will also be adding a 4oz. bottle of the XL-3 Ford FM. I bought 2 bottles, as some on here have said to use 1 and some say use 2. I called 2 dealers today and one said use 1 bottle and the other said use 2. I did not mention to them im using royal purple.

I want to know what you think. If im going to use 2 i would rather go ahead and dump them in, rather than try to top it off with a 2nd bottle after filling up to the hole on the diff.

Thanks guys!

Page 293-294 of the owners manual states the on the 8.8 and 9.75 it takes 4 oz. On the 10.25 it takes 8 oz.

knowing what I know now, I will automatically put 2 bottles in next time to avoid having to go back in. It can't imagine how it could hurt in any way. But i didn't use Royal Purple.

Personally if I was you, I would add one bottle since they say you need none.

Hey, and worse come to worse, if it's not enough modifier, it just causes a slight shudder when performing low speed turns, nothing you can't live with until you find time to crawl under for 5 mins. I had to add a second bottle so I took my little ford bottle of modifier, and a paper cup and got a siphon going. (yes had to spit about 20 times after) and fill the cup until it looks the same quantity as your little bottle. Then squeeze your bottle in, fill the bottle with the fluid from the cup, and top it up. It really took less than 5 mins. lay right on the pavement, no lift or jack or anything needed.