2001 F150 differential fluid change

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Schmoe

Schmoe

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My 2001 F150 Screw has the dreaded differential leak coming off of the pumpkin. Fairly common for this production run from what all I've been reading. Going to get a new cover and change out the fluid, but having a hard time determining exactly what I got. There are two rear taga on the outside of the cover. One says 75W-140 synthetic fluid only. The other one (bear with me)..the top line looks like: S 941 A
the second: L55 9 75 OE11
Does that mean I have a 9.75 inch outer ring? To order the cover, I have to pick a 10.5 or a 9.75. I know it's limited slip from the L. Also, anyone know exactly how much fluid to put in it. I've read anywhere from 4 quarts to a little over 2 along with the 4 ounces of friction modifier....can I get away with using a fluid that has the friction modifier already in it? appreciate any reply's.
 
I tried....they seem to all be different for some reason. I think the last series is the year/month when it was made.
 
Unless you have a 7700lb heavy payload version, you've got a 9.75" rear end. (Assuming you have the 5.4. 4.6l trucks got the 8.8).

The other tag confirms you have a 3.55 LS 9.75 axle out of an F150.

Is the actual cover leaking or is it leaking from the RTV seal, pinion seal, or abs sensor?

Not sure why a new cover is required here.
 
You have the 9.75 rear axle. The bigger axle has 7 lug wheels and came on the F-150 7700 I believe. Add the 4 oz. of friction modifier if it's limited slip even if you use fluid that claims the modifier is not needed. Seems to be hit or miss whether you get rear chatter without the modifier. Also, the diff should take about 2.5-3 quarts plus the modifier to fill IIRC.
 
Originally Posted By: Schmoe
My 2001 F150 Screw has the dreaded differential leak coming off of the pumpkin. Fairly common for this production run from what all I've been reading. Going to get a new cover and change out the fluid, but having a hard time determining exactly what I got. There are two rear taga on the outside of the cover. One says 75W-140 synthetic fluid only. The other one (bear with me)..the top line looks like: S 941 A
the second: L55 9 75 OE11
Does that mean I have a 9.75 inch outer ring? To order the cover, I have to pick a 10.5 or a 9.75. I know it's limited slip from the L. Also, anyone know exactly how much fluid to put in it. I've read anywhere from 4 quarts to a little over 2 along with the 4 ounces of friction modifier....can I get away with using a fluid that has the friction modifier already in it? appreciate any reply's.


If you go to a dealer and ask, they can probably print out a build sheet for the vehicle by VIN which lists every component from the factory. I have one for each of my Chrysler vehicles. I use the info to look up on the Amsoil website for a recommended gear oil.
 
Thanks!! Yeah, it's the 5.4, forgot to mention that. It has the 5 lug wheel pattern. It's diffinently coming from the bottom of the cover. One thing I haven't tried is re-torquing, but from what I've been researching, it's a common problem. With that in mind, I decided to go ahead and replace the cover since that may, or may not, be the culprit. Figure once I'm in there, just "get 'er done."
 
One more thing.....I'm sure the covers are the same, but would it really matter if I got the larger 10.5 inch cover? I'm thinking both would fit but with a slighltly larger cover, I could put more gear oil in it. Makes sense or stick to the correct size?
 
No, do not get the larger 10.5" cover, it won't fit. The cover for the 9.75 sterling is specific to it. Use a splash of LS additive in your oil and don't over do it.
 
If you want an oversize cover with more capacity, Mag-Hytec is the only company I know of that would make such a thing.

However, I don't see why it would be needed in an unmodified truck.
 
Finally got everything together and going to get after it. New cover has a gasket. Do I still need to put permatex around the bolt holes or will the gasket suffice? Using syn. M1 with LS additive added to it. Other forums say dump the seperate LS additive in with it, others say don't...not sure what to do. When I fill it up, am I to fill the gear oil all the way to the top of the fill hole? Or is it suppose to be somewhat lower than that?
Appreciate any inputs.
 
In my experience I usually need half a LS treatment along with the fluids that say that have it built it. A full treatment - results with a lazy LS, and no treatment I feel binding pulling out of side streets.

I've never used a gasket in the chryslers and jeeps. I've always just used black rtv, following the directions. 1/8" beat, includes surrounding all bolt holes. let it tack just a minute, install it about half tight. let it set for an hour or so. finish tightening, add fluid.

I always add fluid to where it starts to spill out then pop the plug in there.
 
What kind of gasket came with the cover?

If it's a paper gasket, throw that away and just use RTV. RTV by itself is more effective than paper or paper + RTV.

If it's a reusable rubber gasket, or an o-ring style seal that fits in a groove, just put a thin film of gear oil on it and assemble.

You should not need any additional LS additive if you are using a fluid that has it. If you do notice chatter, you can always add a little more later, but you shouldn't need it.

You generally just fill to the top of the fill hole. I have seen some instructions to fill to slightly below the fill hole in some applications, but I would bet that's mostly to prevent spills. Won't make much of a difference on a vented solid axle.
 
Well, almost a year now since I've changed it out. I get that shuddering feel when I first take off in the mornings. More noticeable when it's cold out. Once it's been driven for a while, gets warmed up I guess, it goes away. Any ideas? I put in M1 with friction modifier AND the 5 ounce tube of friction modifier....too much?
 
I used the Motorcraft Synthetic diff fluid for my Mustang, with one bottle of the Motorcraft friction modifier, no shudder at all smooth in all weather. I would try that combo.
 
It wasn't from Ford....forgot exactly the name, but it wasn't Ford. Is the shudder a tell-tell sign of NOT enough friction modifier? I could add some more but I don't want to kill that rear end. I pulled my boat right after I swapped out the fluid for about 4 hours and it pulled fine.
 
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