Gear oil choices for 3.92 LSD

[keanezheng]

I have researched around this. It seems like most people go with Amsoil and may or may not add Mopar Friction Modifier. I have 3.92 ratio + LSD.

I am thinking: Redline 75w85 for the front (cheaper and easier to get than Mopar, exact weights as the manual), Valvoline 75w140 (cheaper than Mopar and Amsoil), 2 bottles of Mopar friction modifier due to 5oz needed

Total is around $41 for 2 Redline on Amazon, $46 for 3 Valvoline on Amazon, $25 for 2 Mopar modifier on eBay, plus taxes, and all come with free shipping.

Any suggestions for this?

 

[RAL]

Use what is specified by Ram in the owne’s manual. Don’t over think it. If Amsoil has an equivalent that is fine but typically Amsoil is very expensive and while it is good oil, I can see no point in spending more when lubricants in the correct specification from any other oil company will be fine.

 

[CHeYeNNe71]

I'd stick with same brand fluid front and rear. You can run 75W90 ( front ) which is easier to find usually if I remember.

 

[knightro84]

I'm running the Amsoil Severe Gear 75W-90 in the front and 75W-140 in the rear plus the Mopar friction modifier.

 

[SD Rebel]

On a side note, I think I heard for our diffs that full isn't the typical fill until it leaks out method, it's something like 1/8" or so inches from the fill hole?

 

[CHeYeNNe71]

On a side note, I think I heard for our diffs that full isn't the typical fill until it leaks out method, it's something like 1/8" or so inches from the fill hole?

I'll have to research that, because I plan on doing mine, come Spring.

 

[SD Rebel]

I'll have to research that, because I plan on doing mine, come Spring.

It may not be the case, but you definitely want to double check.

Here is a thread about it: Check your rear diff fluid level

 

[keanezheng]

On a side note, I think I heard for our diffs that full isn't the typical fill until it leaks out method, it's something like 1/8" or so inches from the fill hole?

I have heard about that too, while on YouTube everybody seems to fill till it drips...will that hurt? I can't imagine that if everybody is already doing the leaking out way

 

[keanezheng]

I'm running the Amsoil Severe Gear 75W-90 in the front and 75W-140 in the rear plus the Mopar friction modifier.

Thank you, even with Amsoil you need to add Mopar modifier?
No issues if we run 75w90 in the front?

 

[SD Rebel]

I have heard about that too, while on YouTube everybody seems to fill till it drips...will that hurt? I can't imagine that if everybody is already doing the leaking out way

I don't think it will hurt, just not accurate. But more importantly, people may have erroneously thought their diffs weren't filled correctly when they checked by removing the plug and saw nothing drip out.

 

[keanezheng]

In that case, anybody running Valvoline 75w90 and Valvoline 75w140 + modifier? That seems the most economic yet mainstream brand

 

[knightro84]

Thank you, even with Amsoil you need to add Mopar modifier?
No issues if we run 75w90 in the front?

I'm running it with the mopar friction modifier and have not noticed any adverse reaction. The LSD works as it should. I also haven't had any issues running 75W-90 in the front. I filled both until it started dripping from the fill hole and it was extremely close to the factory fill spec.

Unless you're absolutely beating the hell out of it in 4WD a lot, the difference between going with a full syn Valvoline vs Amsoil is probably going to be non-existant.

 

[CHeYeNNe71]

In that case, anybody running Valvoline 75w90 and Valvoline 75w140 + modifier? That seems the most economic yet mainstream brand

I ran Valvoline SYN in my Grand Cherokee with no issues. I didn't have locker, so didn't need the modifier.

 

[keanezheng]

I'm running it with the mopar friction modifier and have not noticed any adverse reaction. The LSD works as it should. I also haven't had any issues running 75W-90 in the front. I filled both until it started dripping from the fill hole and it was extremely close to the factory fill spec.

Unless you're absolutely beating the hell out of it in 4WD a lot, the difference between going with a full syn Valvoline vs Amsoil is probably going to be non-existant.

Did you add 5oz as the manual says, or added something less? I assume Amsoil probably also contains some of that in it

 

[Scram1500]

Found this on Amsoil's website when I did mine and used 5 oz of Mopar friction modifier. The kicker here is the modifier comes in 4 oz bottles. I've tested it many times, lock up is good

 

[GMetal]

Manual states LSD 3.92 gear requires Synthetic 75W-140 MS-8985 plus 5oz limited slip additive MS-10111

 

[Cbty2050]

I run 75-140 front and rear. Non issue

 

[Mountain Whiskey]

Drain it and then squirt some brand name synthetic gear lube in that your local Walmart has on hand. If it chatters put in a few ounces of friction modifier.

To the fill plug, 1/8 inch down, really? Bust out the eyedropper to be sure.

If you drive in water over the pumpkins for more than a splash or you put 60k on it cruising the mall parking lot, repeat the above steps.

It's just a pickup truck....

 

[1BADRAMLIMITED]

I'm running the Amsoil Severe Gear 75W-90 in the front and 75W-140 in the rear plus the Mopar friction modifier.

SAME! NO ISSUES I ALSO MADE SURE TO CONTACT AMSOIL PRIOR TO PURCHASE AND THIS IS WHAT THEY RECOMMENDED

 

[kdoublep]

I just did my rear diff with Amsoil severe gear 75 140. I used 1 4oz bottle of Mopar modifier first then topped off with gear oil even though Amsoil says the modifier is in there. She's running great.