2001 F150 differential fluid change

[The_Eric]

Originally Posted By: Schmoe
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?


Shuddering while taking off? In a straight line?

 

[Schmoe]

Taking off first thing in the morning or when it's been sitting for a while. I just have a feeling that it's temperature related. Seems like it doesn't do it as much when it's 80 or above.

 

[CarbonSteel]

Originally Posted By: Schmoe
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."
I know it does not help you now, but I had one from my 2010 FX4 that I tried to give away a few months ago (I would have even paid the shipping). You should have the 9.75" model, but I also doubt the cover is at fault unless it was damaged in some way. They do not use a gasket, they use RTV to seal, so you can likely just take it off and clean it and reseal with fresh RTV. Are getting a good price on an OEM? If not, you may want to look at a third party cover.

 

[blupupher]

Originally Posted By: Schmoe
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.

The shudder is a sign of the clutch plates not releasing/slipping enough, which is usually cause be not enough (or incorrect) FM. It is usualy when turning from a stop or going slow and turning. If it is doing it going straight, it could be the clutch packs going out.

 

[meep]

^^^ how would going straight introduce LSD shudder?

 

[Schmoe]

Let me re-phrase that.....I guess it's not straight after all...you would notice it after coming out of a turn, say like your garage as you turn and start to straighten out. The more I think of it, it's never been doing that dead straight. What gets me....I used gear oil with FM in it, then ADDED the 5 ounces of FM....did I "over FM" it??

 

[Schmoe]

Anyone got a take on this?

 

[Schmoe]

Never mind. I found the answer. Translated more to layman's terms, it helps keep the clutchpacks from "sticking" after they've been forced together. It doesn't actually change how the oil lubricates metal parts, it just prevents the clutches getting "stuck" together. So if your having that shudder feel, it means more than likely you'll need more FM. Adding too much FM won't hurt anything.

 

[dakota99]

Yeah I was going to say you won't really hurt anything if you add too much. I tried straight Mobil 1 LS and my 8.25 chattered so I had to add extra modifier to it.

 

[CarbonSteel]

Originally Posted By: dakota99
Yeah I was going to say you won't really hurt anything if you add too much. I tried straight Mobil 1 LS and my 8.25 chattered so I had to add extra modifier to it.
A few of the differential guys have stated that too much FM can impact the gear oil and may cause it to break down. How much is too much would be the question--2x as much? 3x? Molecule may be able to answer that...

 

[Schmoe]

I may just add one more bottle, 5 ounces, and then be done with it...OR....just live with the shudder.

 

[CarbonSteel]

Originally Posted By: Schmoe
I may just add one more bottle, 5 ounces, and then be done with it...OR....just live with the shudder.
I would slowly add and drive until the shudder disappeared. I doubt that shudder is a good thing to have in an LS differential--definitely a sign the clutches are grabbing.