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Planning on doing an Amsoil diff fluid change with their 75W-90 fluid and got their Slip Loc additive. Does anyone know if I should use the whole 4oz of the Slip Loc additive or partial? Anyone do this care to chime in?
 

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2019 Challenger Hellcat Widebody (destroyer grey)
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I believe you would use the whole 4oz bottle of the slip lock. At least I did in my Ford super 8.8 diff in my S2000..
 

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2015 Charger SRT Hellcat
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AMSOIL synthetic gear lubes are limited-slip capable and do not typically require an additional friction-modifier additive. However, depending on the differential’s friction material and degree of clutch wear, chatter can still sometimes occur. The addition of AMSOIL Slip Lock will eliminate chatter in mechanically sound differentials.
 

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@16GoManGoHC as I'm 99% sure he uses that fluid in his diffs and beats on his car hard. He'll probably know for sure if you need additional additive. The severe gear fluid already comes with some in it but Amsoil will advise that some friction materials require additional to be added to prevent the chatter.
 

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Soooooo. Add or not add? What is better for our diffs?
On the friction modifier bottle, it will tell you how many quarts the full bottle can treat. I believe the Amsoil modifier treats 1oz per quart. Ive done the rear fluids 5 times now between my cat and a couple of my buddies, and every time we put about 1.5 quarts (Stop when it drips out of the fill port) and have put 2oz of the modifier. I have only used the Amsoil slip lock and have had 0 problems. Our differentials are LSD therefore friction modifier should be used. Hope this helped!
 

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2019 Challenger Hellcat Widebody (destroyer grey)
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I just filled a brand new 3.90 Diff last night with about 1.2 Qts of 75w90 Severe Gear, I added 1 oz of Mopar Slip additive to the first qt, shook well, and it performed well. Did it’s first 3 1/4 mile pulls 10 miles into its life, performed well, no slip, no chatter, no noise.

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Just curious why you're not using the Amsoil slip loc?

I haven't run my super 8.8 yet since the car is still being built but I hope adding the whole 4oz of slip loc was ok. LOL
 

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This is how it was explained to me:

Put in the gear lube, go find an empty parking lot, do some figure eights, and listen for chatter (that'd be the clutch packs sticking, fighting friction, wearing out and slipping harshly instead of smoothly).

No chatter - you're good.

Chatter present - add 1 or 2 oz of friction modifier (FM) and repeat test above.

No chatter - you're good.

Chatter still present - add another 1 or 2 oz of FM and repeat test above.

Add enough FM until the LSD clutches are happily quiet and slippy. If you add too much though it'll slip too easily acting like an open diff and defeat its purpose. So limit yourself to just one of those tiny 4 ounce FM bottles/tubes.
 
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Just curious why you're not using the Amsoil slip loc?

I haven't run my super 8.8 yet since the car is still being built but I hope adding the whole 4oz of slip loc was ok. LOL
I had the Mopar stuff on hand already.
I added 1 oz to a QT, shook it well, put it in the Diff, added 4 oz’s from another just opened Qt, shook it well, put that in the Diff until it ran out the fill port, plugged it. I didn’t feel like revisiting under the car again so I just started off with an oz, Diff acts good, no slip, no chatter in tight circles, all good. Next time under the car over winter I’ll remove the fill plug and see what is on the magnet.
 
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