12" AAM rear diff 'anti spin' - Page 7 - Dodge Cummins Diesel Forum
4th Gen Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine, Transmission, etc...NO ADVERTISING

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post #73 of 89 (permalink) Old 05-17-2019, 08:30 AM Thread Starter
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Iíve been running Mobil 1 75-90 for 100K miles and my limited slip works as well as it did on day one. Mobil claims no friction modifier needed because itís already in the additive package of the oil. It also works well in my wifeís 06 GTO so I believe their sales pitch.
But Mobil One does include the friction modifier in it. So you are good. MOPAR 75w140 specifically says it need the FM on the bottle


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6.7 HO Aisin AS69RC. Borg Wagner 44-48 4x4. 12" AAM Rear end. CCLB. Single Rear Wheel. Max Steel. 295/70/18 (35x12) Mickey Thompson MTZ P3. No lift/no level.
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post #74 of 89 (permalink) Old 05-17-2019, 10:47 AM
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MOPAR 75w140 specifically says it need the FM on the bottle
That would depend on what type of diff the oil is going in.
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post #75 of 89 (permalink) Old 05-17-2019, 12:07 PM
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the 1500's call for 75w90. Mine (as well as the other 3500's to my knowledge) calls for 75w140 synthetic.
Did they change the fluid spec for 2019s? They specified 75w85 for previous years with the AAM axles.
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post #76 of 89 (permalink) Old 05-17-2019, 12:24 PM Thread Starter
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That would depend on what type of diff the oil is going in.
Right. The label just says thereís no additive in it. But if your diff doesnít call for it, then itís ready to go out of the bottle. Of course, finding out which exact diff is in my 12Ē AAM is like one of lifeís great mysteries. But I am making progress due to help from this board.
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post #77 of 89 (permalink) Old 05-17-2019, 12:28 PM
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Right. The label just says there’s no additive in it. But if your diff doesn’t call for it, then it’s ready to go out of the bottle. Of course, finding out which exact diff is in my 12” AAM is like one of life’s great mysteries. But I am making progress due to help from this board.
I'm not sure about the 12", but the AAM's on the previous years claimed no additive was necessary, but some people are getting chatter and said adding it helps. Also, on my '02 1500 it required additive but I still had to add extra additive to fluids that already contained it. Each diff has it's own personality apparently...

As for finding out what's in yours, jack up the axle and see if one wheel is free or not. Previous 3500s all had limited slip I believe.
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post #78 of 89 (permalink) Old 05-17-2019, 12:36 PM
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I would suggest putting whatever 75W/140 in there that you like. Then, if it doesn't perform properly without it, add some friction modifier.

After all, there are people putting FM in open diffs and (real) lockers, and others that run clutch type diffs, which may or may not need it, without any friction modifier. And it still all seems to work fine for the most part.

Personally I wouldn't add a thing unless the diff was misbehaving, since it most likely will perform better without any additives.

Maybe if we start telling people that the brain is an app, they will start using it?

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post #79 of 89 (permalink) Old 05-17-2019, 12:48 PM
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Actually, my 2015 3500 calls for 75-85 . The reason for my post was in reply to concerns about Torson style diff operation with the modifier included. That being my limited slip works fine using it as well as my wife’s GTO which has clutches.
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post #80 of 89 (permalink) Old 05-17-2019, 01:55 PM Thread Starter
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I'm not sure about the 12", but the AAM's on the previous years claimed no additive was necessary, but some people are getting chatter and said adding it helps. Also, on my '02 1500 it required additive but I still had to add extra additive to fluids that already contained it. Each diff has it's own personality apparently...

As for finding out what's in yours, jack up the axle and see if one wheel is free or not. Previous 3500s all had limited slip I believe.
It definitely has limited skip. The question is which limited slip.
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post #81 of 89 (permalink) Old 05-17-2019, 01:58 PM
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Quote:
Originally Posted by Lins View Post
I'm not sure about the 12", but the AAM's on the previous years claimed no additive was necessary, but some people are getting chatter and said adding it helps. Also, on my '02 1500 it required additive but I still had to add extra additive to fluids that already contained it. Each diff has it's own personality apparently...

As for finding out what's in yours, jack up the axle and see if one wheel is free or not. Previous 3500s all had limited slip I believe.
It definitely has limited skip. The question is which limited slip.
If the manual requires modifier it should be clutch pack, if it still doesn’t require modifier then it should be torsen style.
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post #82 of 89 (permalink) Old 05-17-2019, 02:01 PM
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If you really want to know pull the cover, the gasket is likely still the reusable type.

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post #83 of 89 (permalink) Old 05-17-2019, 02:14 PM
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If the manual requires modifier it should be clutch pack, if it still doesnít require modifier then it should be torsen style.
We already know that it's not a helical gear type. That's obvious from the photos.
So if it is a clutch type, it may work fine without any friction modifier, and if not, then some could be added.
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Maybe if we start telling people that the brain is an app, they will start using it?

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post #84 of 89 (permalink) Old 05-17-2019, 02:32 PM
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Apparently, it is a clutch type and does need the modifier.
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It definitely has limited skip. The question is which limited slip.
Are we having brain farts here?
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