2000 Expedition rear Diff
 

Yes the title does say Expedition. I had a quick question regarding my dad expedition and well all i own is a f150 but i figured it the rear diff might be similar so some f150 trucks. Feel free to remove this post from here if not allowed.

So last couple days he has been having issues with his rear diff. Its been having issues when doing slow turns like at intersections, i believe this is an issue either with the diff fluid or diff clutches. I also think from my research that he does not have an LSD because when lifting truck on jacks and attempting to spin tires the spin in opposite directions.

Here is the main question. When we were trying to spin the tires they were extremely hard to turn in either side. It would take a lot of force to be able to spin it just a bit. I have not been able to find much on the internet regarding this specific issue. Any of you guys have any idea what this could be caused by? We also just removed the cover and did not see anything wrong with the Diff like shavings or anything broken. Replaced with new Synthetic diff fluid and a bottle of friction modifier but we have not drove it much since last night.

Also truck is 5.4 with the A4WD option and had i believe a 12 bolt diff cover
Thank you guys in advance for any input on this issue.

It's most likely LS. Just look in the door jam for H9. Mine did the same years ago, it's the clutch pacs. After changing the fluid, it took awhile but it quit slipping when turning from a dead stop. I have 60,000 more miles on it now and it slips every now and again, so it's ready for another change.

Just an FYI... on any Ford axle code, if it has a letter it is an LSD. If it is just a number, it is not an LSD.

So H9 means nothing then ? Well mine has H9 and it is LS.

Yes, I believe that is a 3.55 LSD. The fact it starts with a letter means it is an LSD.

Was that post confusing?

No, not now lol. Oops.

Was reading online some other people having somewhat of a similar issue but it had to do with the A4WD not disengaging. Disconnected 4wd fuse and transfer case harness and no change so im really hoping that after some more time with the change of fluid it gets better like Jbrew mentioned.

Also i thought that if you spinned a tired one way and the other spinned the other way around then its not a LS diff. Like the follwoing video

If it's in park and a LSD it will be hard to turn and they will spin opposite directions

it was in neutral

It just needs new LS clutches. Very common for the 9.75 axle.
-- I missed the part about new fluid until just now. It MIGHT quiet down, run it for a while and see. My experience with older/higher mileage LS units is once they begin to squawk it takes clutch replacement to fix it.