What Gear Oil Do You Run in Your Diffs...

[cre1992]

I just recently ordered some new diff covers for my truck and plan on changing the gear oil in the diffs as I have no idea when the gear oil was last changed since I bought the truck not running.

So that leads to me to my questions. I am a big proponent of using Amsoil in just about everything. However upon looking into what is recommended for the trucks, I am coming up with 80W-90 for the front diff (Dana 60) and 75W-140 for the rear diff (10.25LS). I plan on running Amsoil, and even though their gear oil has friction modifiers in it, I plan on running 4oz of their friction modifier just to be on the safe side.

Amsoil recommends:
80W-90 in both diffs, but also suggests 75W-90 and 75W-110

What weight gear oil are you running in your diffs?

What brands are you using?

 

[david85]

75W-90 Synthetic

 

[03wr250f]

All the research I have found and testing I have seen is amsoil, royal purple, and mobil are very close in tests, and I am currently running royal purple in my tcase and rear diff.
Mobil 1 in my front diff
I will now run Mobil 1 in everything. $10 a quart lower than royal purple and basically same protection/test results.

That being said if like amsoil. Run it. It won't hurt, I just feel like I can spend money better other places
That being said my front has 75-90syn and when I swap I will fill with new syn.
Rear same story but with 75-140

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[IDIBRONCO]

I currently have dino oil in everything, but I'm thinking about switching to synthetic (I'm not sure on the engine yet). I haven't even thought about what viscosity to run. After reading 03wr250f's post, I do think that I will be using Mobile 1.

 

[CDX825]

Amsoil severe gear 75W110 in the rear diffs 75W90 in the fronts.

 

[Cubey]

The Dana 70 in my RV has conventional SuperTech 85w-140 because it's cheap ($17/gal) and my differential was very dirty when I got it, probably the original oil from 1985.

I ran conventional SuperTech 80w90 after the initial drain, cover cleaning, and refill. After about 2k miles, I did another drain and changed to the 85w-140.

Maybe some day once I feel it's been cleaned out enough with the $17/gal SuperTech oil, I'll put in some kind of synthetic.

Being an open differential, I can give it any kind of gear oil basically though, so the SuperTech oil is good enough for the short OCIs I'm doing with it.

Oh, and I have a LubeLocker reusable gasket on it, so no RTV/scraping to open it to change it. The gasket has already paid for itself vs paper gaskets and RTV.

 

[u2slow]

, I am coming up with 80W-90 for the front diff (Dana 60) and 75W-140 for the rear diff (10.25LS). I plan on running Amsoil, and even though their gear oil has friction modifiers in it, I plan on running 4oz of their friction modifier just to be on the safe side.

Amsoil recommends:
80W-90 in both diffs, but also suggests 75W-90 and 75W-110

Beware that friction modifier is a 'just enough' type thing. Add lots and you defeat the traction aid to some extent. I've always left it out to get the most grip I can.

I've been running the cheapest 80w90 I can find for over 20 years. (usually Wal-Mart). Murphy's law predicts the costlier the oil, the greater the chance you have bust into the diff again for something.

 

[WarNose]

The way I understand it is that if you use 75w-140 that it must be synthetic and synthetic usually doesn't need any friction modifier added. It should say on the bottle.

 

[nitroguy]

Super tech here too (cheap from walmart).

I use 75-90 front and rear, but I don't tow heavy at all, and more than hot days we get cold days so I figure the thinner oil on cold days probably helps a little.

So, my advice is worth what you paid for (nothing) but that's my theory anyway. I also only travel less than 8k miles a year, even though it's my daily driver. With that type of mileage, I could probably get away with nonfat milk in my diff and still be ok on this old iron.

 

[264WSM]

I run 75-90 Amsoil in mine. 2 stories:
Big truck diff manufactures (Eaton, Rockwell, Spicer...) will warranty diffs for 250K miles if they are spec'ed with dino oil. If you spec them with synthetic, they warranty them for 750K miles

A friend ran his 10.25 Sterling out of oil and locked it up. Several days later he filled it with oil (guessing dino oil) started the truck and drove it home!! I can't explain it, but those diffs are tough!

 

[tjsea]

Speaking from experience don't add the Amsoil friction modifier unless you have chattering issues. That is what I remember reading on their site back when I did mine. I made the mistake of adding it right away and my lsd no longer works as good as it did prior. From what I've read the synthetic oil alone is many times enough and by me adding the friction modifier it became too much for the lsd. I plan to drain and refill sometime without the friction modifier, but I just haven't gotten it done yet.

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[12pilgrim]

I know this thread is old but in case anyone else is interested I found this to be eye opening:

1986 Ford F-250 HD Towing Axle - Four Wheeler Magazine

Heres how to build a real towing axle! We used a 1986 Ford F-250 HD in Four Wheeler Magazine.

www.motortrend.com