New AAM 11.5" POSI...which diff fluid?

[jonathancasey19]

Just installed new Yukon ring/pinion gears and a AAM 11.5" POSI unit. Time for 500mi change. Which diff. fluid would you recommend? I've always used 75w-90 synthetic with factory G80 unit.....Also my area hardly sees below freezing in winter.

75w-90 Synthetic

OR

85w-140 Non-synthetic

Company I purchased gears and 11.5" POSI from told me....

"85w140 non-synthetic is what we recommend for all differentials. You will also need a posi additive such as trans-x which can be purchased at most auto parts stores."

Anyone used non-synthetic & additives with their posi's?

Thanks

 

[S Phinney]

Johnathan I always use synthetic oils in those items. Synthetics hold up to heats better.

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[OregonDMAX]

Johnathan I always use synthetic oils in those items. Synthetics hold up to heats better.

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You can't always assume synthetic is better, if the mfg. Says non-syn w/additive then thats what I would do. I've replaced quite a few Tacoma/FJ posi diff's because the owner thought synthetic was better and the clutches got fried, those had to have the non-syn w/additive to keep the friction down. Most of the time the additive is a friction modifier.

 

[jonathancasey19]

Correction......I received another response. He still recommends non-synthetic; however, no additive.... see below:

"Lucas 85 w 140 non synthetic is what we recommend. For your particular Posi no additive is recommended. This is a different response then you previously received and this response is correct. No additive is required and standard dyno non synthetic is what is recommended. Thanks, Chase"

 

[OregonDMAX]

The best answer you could get is straight from the mfg. Good that they responded :thumb:

 

[PACougar]

Who makes the posi unit?

 

[Chevy1925]

The fact they cant get their info straight on a posi unit that has no clutches in it makes me wonder if their info is even correct for diff fluid recommendations. sounds more like your talking to a sales guy who doesnt know his tech

Johnathan, id throw synthetic in it. plenty of guys running that diff with full syn in it and no issues. the fact its synthetic would have next to no issues with that diff based on its operation.

 

[Chevy1925]

Who makes the posi unit?

its a factory AAM unit, in otherwords, its a dodge limited slip

 

[Evan@InglewoodTrans]

If its synthetic or billet it's better duh.

 

[PACougar]

The Dodge unit's don't have clutches and I've ran synthetic with mine for the last 100K miles. I wouldn't trust the sales guys at the place you bought it from.

 

[jonathancasey19]

The sales guy sounds like he doesn't know his head from his ass. I bought the posi unit (helical style-no clutches) and yukon gears from East Coast Gear Supply in Raleigh, NC.

I've always used synthetic gear oil. Still up in the air at this point. The use of a posi-additive is another question. I don't know enough about these units if I should use additive or not.

 

[OregonDMAX]

If its synthetic or billet it's better duh.

You made me laugh so hard :roflmao:


I thought you sad it had clutches, after looking back i see you never said that so at this point synthetic would be fine, I wouldn't think twice about it.

 

[thunder550]

If its synthetic or billet it's better duh.

This made me giggle :rofl:

 

[BHoward6.6]

I recently installed a Eaton True Track in my 11.5. I called Eaton tech about what diff fluid to use, they recommend non synthetic with no additive. I went with Lucas 85w140.
My truck has 195,000 miles on it, half or more was towing a large 5th wheel, I have always used Mobil 75w90 synthetic, my diff and bearings were like new.

 

[IronDX]

Id use 75W-90 synthetic gear lube.