Friction Modifier

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Apr 30, 2016
Hi All,

Looking for some input from other users here. A while ago I did a full differential fluid change. I filled it with the recommended type (75W-140 Motorcraft, no modifiers in oil) and amount and added the recommended 4oz of Ford XL-3 friction modifier.

Everything seemed alright but I have noticed that the chatter in the rear end is back somewhat. I find that particularly on hard launches (even on straights), making even an average launch while going uphill from a standstill, and making a quick right hand turn from a stand still there is a decent amount of stuttering/chatter.

At first I thought it was the drive shaft as I had to remove it to put a new gasket on the output shaft of my transmission, and it felt as though the chatter was originating from there, but everything appears to be in order there.

As this seems to be a textbook case of not having enough friction modifier in your differential, would it hurt to add another 4oz of friction modifier? I have read some people having success with this while others are dead set against going above factory recommended specs.

TL;DR: Chatter has developed. Has anyone added above the recommended 4oz of friction modifier to a Ford 8.8, limited-slip differential. Any negative consequences?
Sometimes you have to add a bit more. The best way to mix it in is to do figure 8's. When we do a fresh build with new clutches we soak them in XL-3 before they go in the center section.
Are you open to using a different brand of Limited Slip additive? We have had good results with Lubegard Limited Slip Additive. I used Amsoil Severe Gear and their Slip Loc additive in our SUV. At first, it was fine, but, after towing a 12 foot cargo trailer on Saturdays to the Farmer's Market, it started clunking and banging.
Change it out to Mobil 1 gear lube. I tried the Mobil 1 without any additives first, since it says it has the limited slip additives already. It was fine doing straight acceleration, but, going around turns, it chattered. Added the Lubegard additive, and it has been fine since. Three years later, and it still doesn't chattered around turns.

Our dad's 2006 Tundra had clunking and banging when we tried to use just gear lube with no additive, even though the gear lube said it had additives already and additional additives shouldn't be necessary.
Appreciate the replies.

It sounds as though that if I do not get crazy with adding too much modifier, I should be alright. I am definitely open to using other brands, but I think I will first try pumping out 4oz from my differential and adding another bottle in. I figure this should leave me anywhere from around 6-7oz of modifier in total.

If the chatter continues I will definitely give Mobil 1 a look along with some Lubegard. I have seen these recommended by others before, so I figure it would be worth a shot.

It shouldn't chatter while going straight unless one wheel is breaking traction.....Which shouldn't happen with a Posi/Limited Slip with both tires on dry pavement.
like everything else Redline their gear lubricants are the best, check their web or call + TALK to a tech for recommendations !!
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