Hi All,

New-to-me e99 F350, 4X4, SuperCab, Long Bed. Removed rear diff. cover, drained, cleaned mating surfaces, wire wheeled & painted cover, new UltraBlack RVT, refilled.

Door sticker says non-posi. "Axle 41"


How's the condition look?












It's the 10.5, right?








The capacities I have are:

3.44 QUARTS of 75W 140 synthetic oil



236.56 mL friction modifier (2+ bottles of this?)



The outside of the cover had some shallow pitting and at a certain point I didn't want to take off all the metal around it with the wire wheel.



The inside was discolored and had some pitting on the inside radius edge.




I'm VERY new to these trucks, and somewhat new to automotive work, though I've neve worked on a Differential.....

Thanks for any input you may have!

-Will

 

Looks to me like you have a locker in that.

 

I have all the parts to do this job in the next week or two. I didn't like the look of the rust on the outside of mine so i bought a cover. curious to see what the experienced crew has to say on this. it will be my first time as well.

 

Is it the original rear axle? Don't quote me but I think the OEM Sterling rear end was a 10.25 until around 2001 give or take. Hopefully somebody will chime in and correct me if I'm wrong.

 

99 or 99.5 is when they changed to 10.5"

 

It very well may be a Limited Slip differential. I would be cautious on using the friction modifier. A simple way to check the differential is jack one wheel off the ground and see if you can turn it with it in neutral. Chock the wheels first to make sure it doesn't roll away! If in fact it is a L.S. differential, Guzzle has a good recommendation on how to use the Friction Modifier.

Welcome to guzzle's Rear Differential Maintenance Web Page

If it is not a L.S. differential, friction modifier is not needed. If it is, then I would follow his advice on that in the link above. Often, I believe too many people add too much friction modifier to their differential and they no longer have a functioning, limited-slip differential. Guzzle explains how this happens.

 

It's Thursday. I thought you had a trailer to pick up in Rocklin today (postponed from the previous Monday). Now you've got your rear end apart?

 

Thanks for the replies!

It's a simple job. If you're at all mechanically inclined, it shouldn't be bad, especially since you won't be spending time cleaning up the cover. Click on the link to Guzzle's page, that CampSpingsJohn posted, and follow his directions.


Honestly, I'm not sure what's-what on this thing. There's random wiring that's been cut and what look like the vertical pieces of L brackets that have been cut off the frame with a torch. Really big ground wires attached to the frame that have been cut. There's a bunch of stuff like that that makes me wonder what the heck Dr. Frankenstein did to this truck......

It's an early '99 - Door sticker production date, 04/1998. I think the owners manual says 10.5? Hmm.... I'll have to double check......

So, I'll get either of the rear wheels (but only one) off the ground, have the truck in neutral, and attempt to turn the lifted wheel. If it turns, it is NOT an L.S. and if it doesn't it IS an L.S. ie, If it's L.S. the wheels are "connected," correct? Oh, and I won't bother chocking the wheel, I live on a hill. What's the worst that can happen?!

I'd done a bunch of thread searching and finally found that page from Guzzle. Used it as my guide!

Trailer?! What trailer?! The rear end is already put back together. I just wanted to get some input/advice about what's back there. You know, after the fact and when I'd have to take it apart again if I found out something was wrong! I still have to finish installing ALL of the 5er rail hardware. The truck came with rails "installed," but none of the (only 7!) bolts that were in them were properly installed. Being in a hurry, and not knowing any better at the time, is biting me in the...... Luckily the dealer doesn't care that I keep having to delay the pick up. Which is good, because I have to test all the trailer wiring, replace the shift stalk (overdrive stuck on & I tried just replacing the switch), and swap out all the leaf springs! I'll do the rear u-joint and fix the leaking seal in the shift shaft sensor above the tranny pan when I get back?!?! The tranny is doing a weird "wavering" in RPMs when shifting into 4th, too. I've got some thread searching to do!

 

So, chocked the front wheels, jacked up the driver side rear, put it in neutral, and the wheel turned freely. Repeated the same process on the other side, with the same result. Looks like I don't have an L.S. diff. I did put about 3/4 of a bottle of friction modifier in. Anyone have experience with that being an issue?

Thanks for the heads up about the testing method!

 

I would not worry about the friction modifier in there. If the oil level is good and no leaks, it's ready to drag around a trailer.

 

The Ford limited slip has clutch discs. They are kind of similar to the friction disc on a manual transmission clutch.

How it's supposed to work; when you are driving down the road the clutch is engaged, supplying equal amounts of torque to both wheels. When you go around a turn(with good traction), the torque difference between the 2 wheels overtakes the friction between the clutches and the wheels are able to spin at separate speeds so you go around the turn smoothly(with out the wheels hopping). Sometimes the friction modifier is needed to make this happen. So the idea is, in a low traction situation, the clutches will limit the amount of slip between the two wheels and supply some traction to the wheel that would otherwise be free spinning.

In an open diff, there are no clutches, so no need for the modifier or any other special gear oil for that matter. Yours does not look like an open diff in my opinion.