I am planning on changing the oil in my rear axle this weekend. It is the 8.8" version. What type of friction modifier will I need to add? Any brands you would recommend?

 

my autozone only had one brand. However the synthetics available had the modifier already added so none was needed. I use mobile1

 

If you have the factory limited slip, the best to use is the Ford brand one (XL-3). Even with fluid containing friction modifier, many still have issues with the clutches chattering, and adding the Ford stuff fixes it. Just easier to add it at the get go.
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Just be aware this stuff smells worse than death (and I have smelled both). Wear gloves when you use it and just throw away anything that gets it on it.

 

When I read the Mobile 1 bottle ...it states it is for Limited slip diff's... does not state it has the require friction modifier contained in it for our FORD Diff...so...I added a 4oz bottle of friction modifier along with the Mobile 1.

 

I use Royal Purple which has the required XL3 friction modifier. But still ended up adding 4oz of Ford's XL3

 

I've run trak-lok diffs with both Royal Purple and Mobil1 gear oil, without adding any other friction modifier, and I have never had an issue with clutch chatter. As a matter of fact, in high mileage cars and trucks, most of the time the clutches and steels in the diff have worn into each other, and still won't chatter even with conventional gear oil with no friction modifier. The only time I have ever experienced diff chatter on any vehicles, is on a freshly rebuilt diff where I soaked the clutches in gear oil, but without any friction modifier, then added the friction modifier after it was all assembled. In that case, it chattered pretty bad until the friction modifier made its way through everything and to the clutches. Ever since then, when I am rebuilding a diff, I get the Mobil 1 or Royal Purple gear oil, soak the clutches in that prior to assembly, and have never had one chatter on me since.

 

ajr, - are you sure you need it?