Rear end ? Limited Slip or ?
 

Ok, what I thought was sound of the tread blocks is bad. Sounds like it is engaged in 4x4 on dry pavement ,from the rear..aggressive tire sounds are like bearings...
Local guy took it for a spin finally after I had concerns about rattle in front end suspension. He did not notice that but did notice rear end bearing sound...not good. His guys did the fluid switch @ 89k....aks me if it is limited slip differential...
I just assumed it was limited slip differential ..2001 F-150 Lariat 4x4 Offroad....... & I assumed they put the proper fluids in. Sound is very bad from RR & vibrates wheel flairs....not good.

I am taking it to a guy who has shop in Alb. to check & probably trailer to town.I am very nervous about seized LS or rear end bearing now. I will have him drive & listen to frontend rattle & rearend.
I also know local shade tree is not a good idea in long run. Tough being in middle of nowhere in NM...on terrible roads.
Guess's on if it LS or what problem is?

What is the axle code on the door jam sticker? Also there should be 2 tags on the rear diff cover that tells you the gear ratio and whethe it has traction lock.

door code H9

tags are use 140W Sythn only &
S 919 F
L 55 9 75 1B13

Yes, that's a 3.55 LS 9.75" axle. 75W140 synthetic plus a bottle of Ford XL3 friction modifier.

Thank you glc.
I sent pics of tag to guy who will be working on it. He suspects that no additive was added.He uses Ford. He is going to order parts after he looks at it Sat.
I will show him this & the Forum. I cannot believe how many mech's do not know about this page & similar ones,but can play solitaire...lol.
This guy does go by book & has great shop & staff & checked truck when I was buying. I was going to work on my old Tacoma,but it will have to be daily driver again for a while.
Thanks again for info.

My good mech. saved my ...RE.
New inner bearings & proper fluids.
LS still works fine.

What do you mean "inner bearings"? The front has bearing hubs that come as a unit with inner and outer bearings inside.

He's talking about the rear end.

Rear end inner bearings.
Front hubs both trplaced.

LS Additive
 

Hey guys,
Can anyone tell me if I need to add any type of additive when changing the differential fluid for an L9 axle code (3:55 w/e-locker)?

Thanks!

No additive needed for e-locker.

Awesome! Thank you!

OK, after having the RE inner bearings replaced & fluids replaced with friction modifier (all Ford products) I was replacing E-brake cable & noticed differential cover leak...I was 300mi from mech who did work so I had local guy drain,reseal,torque(1 bolt had been missed on rebuild), and fluids replaced(NAPA products). I now have a shudder when I take off from start. Seems like LS part/clutches going or gone to me.
The guy that rebuilt it was going to come down to his place nearby and drive it to check. He said it sounded like the LS friction modifier was not added. But I watched the guy add it. It was the NAPA brand made they say for Ford. The amount that he added was correct by Ford manual. Rebuild guy was also going to bring 2 containers of friction modifier from Ford down this weekend,but did not show.I'm 300 mi away from his shop. He said the clutches could be going and that side can be rebuilt easy too.

My question today is do I need to order Ford Motor products exclusively for this Ford & RE? Does the NAPA brand they say that works for Ford, not work? Do I need to add more modifier than the 4.4 oz that is recommended amount in book?
I really do not want to fry my RE. Shudder goes away after getting up to speed ,but can't tell if it shudders when I hit the rough road parts at speed. Can I use it til I get it corrected,right.
I also do not want to take it to a Ford dealer if I can help it,but will. Then I'll have 3 shops involved. Torn in middle of no where NM.

Adding more friction modifier won't hurt.

I recommend getting a tube or two of the Motorcraft friction modifier.

Frequently, the 9.75" axles need 2 bottles of modifier to smooth them out. I'd buy the XL-3 modifier from a Ford dealer, it's not expensive. Any brand of 75W140 full synthetic is fine. It's safe to drive.