Diffs w/ Aussie Locker - What oil?

[jkane]

I have a recently purchased 2003 4.0 FX4 with front and rear Aussie lockers.

I looked on the Aussie website and they said no special oil is needed, but I have read upon many things saying that it would be best to run a friction modifier.

I would like to get your opinions. Ford recommends:

Front - Motorcraft SAE 80W-90 Premium Rear Axle Lubricant

Rear - Motorcraft SAE 75W-140 Synthetic Rear Axle Lubricant

Would I just add friction modifier to both of these?

Thanks for any help

 

[Captain Ledd]

Synthetics don't need a friction modifier, it's already (essentially) built into the oil.

The friction modifier isn't for the Aussie, it's for the gears and bearings. Hypoid gears still have some sliding friction. If you're using standard dino-oil it'll help things slip a little easier.

With your choices, the rear doesn't need it. And unless it's an AWD vehicle, the front doesn't need fancy oil anyways.

 

[jkane]

Ok thanks. That brings be to my next question, is there any harm to adding friction modifier or using synthetic oil when it is not recommended?

 

[Captain Ledd]

I doubt it. But best use what's recommended.

 

[4.0B2]

Yeah just use what ford says... I just use 75-140 in both. It's what I can get free. No issues. It was new gears and install kits and lockers

 

[4x4junkie]

If it gets cold where you are, a thinner oil will be less likely to cause problems with locker engagement (75W90 should be fine).

 

[adsm08]

Ok thanks. That brings be to my next question, is there any harm to adding friction modifier or using synthetic oil when it is not recommended?

The addition of friction modifier causing problems in your situation is largely a matter of opinion.

How do you feel about wasting money? If you are good with it, then it shouldn't cause any problems. For me, it would be a problem.


The biggest reason for putting friction modifier in a diff is if it has a clutch-type limited slip unit. The clutches will bind and chatter without it. It serves no other purpose.