Question on sythetic differential fluid type.

[Harry5150]

I'm replacing a seal in my diff this weekend and would like to put in synthetic fluid.

It looks like Amsoil is the type most folks here use. What grade should I use? I belive it's 80W90 (Ford #XY-80W90-QL) for a 4.0L 2WD w/ a LS differential.

This is the one I'm looking to get:

Dead Link Removed

Or is the Series 2000 fluid the one I should get. It's a different weight though.

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The owner's guide says that the 5.0L with conventional and LS differentials comes with Motorcraft Premium synthetic already.

Am I to assume that the 4.0L use regular gear oil even thought the axles are the same for both. Is it ok to switch to synthetic?


Thanks,
Harry

 

[RTStork]

I would go with the series 2000. I think that is their top-of-the-line gear oil. The 75W90 will be slightly thinner than the 80W90 while the oil is cold and it should be fine to use. I believe the Amsoil has a limited slip additive so you might not need the friction modifier additive from Ford. If it chatters a little, add 1/2 bottle of the friction modifier and it will quiet the clutch packs.

 

[Robert]

Check my message to Yomie Dead Link Removed For a limited slip in a '97, you need Synthetic 75W140 with the additive. The Amsoil isn't supposed to require the additive it that is what you go with.

 

[Harry5150]

Robert -

Thanks, I just crawled under there and read the tag, "Synthetic 75W140 Only". I though the differential tag only had the gear ratio on it. Learning something new here all the time.

Harry

 

[AgExplorer]

Harry,

The AMSOIL Series 2000 75W-90 will work fine in the differential. And without the friction modifier. The choice of the 75W-140 or 75W-90 is up to you. If you do a lot of towing and/or off-roading, the 75-140 is probably the lube of choice.

E-mail me if you'd like to purchase any AMSOIL product. I'll get it for you wholesale (about 25% off retail). You'll need about 3 quarts of gear lube for the rear diff.