FordCountry

I have an '01 f-150 2wd with the triton 4.6. What kind and of rear diff fluid should I use? Do I need to use an additive? I'm going to replace the cover seal and clean all the old fluid out and put some new stuff in but didn't know what to put in. I know this is a newb question that yall probably get tired of hearing but any advice would be greatly appreciated. Thanks. Also, if there are any other advice on this project would be great.

Kattumaram

75W140 full synthetic only. A limited-slip differential requires a friction modifier added to the lube.

Here is the Ford spec. for lube for a '97 standard axle, yours should be the same:

Synthetic 75W-140 GL-5
Note: Part No. XY-75W140-QL

For a limited-slip axle:

Synthetic 75W-140 GL-5+
Note: Part No. XY-75W140-QL

FordCountry

Thanks Kattumaram. How do I know if my diff is a limited slip? What kind of additive does it take if it is? I really appreciate your reply btw.

partsmark

look at the tag on the rearend . it will be 3l55 that means 355 gear and the l means limited slip. you can get synthetic 75w140 and get xl3 additive at the dealership also.

FordCountry

Ok, I checked out the tag and it does say 3L55 and through further research I found out that the axle code H9 on my door jam means that I have a 3.55 LS Diff. Problem solved. Thanks Guys.

FX4Nick

Correct me if I'm wrong, but a synthetic like Royal Purple does not need the friction modifier, because RP already has this stuff in it.

FordCountry

I've read that too but i figured I'd put it in anyway. Couldn't hurt....

kaboom10

You're wasting your money when using the premium synthetics. They have the friction modifiers in them already. I use Amsoil brand in mine.

FordCountry

I went to the dealership to get the fluid and gasket, they said ford does not offer a gasket for the rear diff. what gives? I found one at o'reilly's but the FORD DEALERSHIP doesn't carry one?

kaboom10

The factory uses silicone as a gasket. The place that did my rear end used it to and it works fine.