which synthetic for rear diff?

[snocross1985]

OK, I have searched and searched but keep coming up with mixed results. I plan on switching my rear diff (and everything else eventually) to synthetic. I really don't want to buy oil online, so where would I be able to buy the synthetic? Also, I have heard that some used 75w90 and some have used 75w140. Which should I use in my limited slip? Do I still need friction modifier? I know that these questions have been answered several times before, but like I said I keep seeing mixed answers. Thanks again.

 

[aldive]

I use this Amsoil....Dead Link Removed

I have never added any friction modifier, however, I shall add it at the next change to see any difference.

 

[jimbo74]

amsoil as well as many of the high performance lubes dont require the friction modifier... according directly to the site aldive posted, it says that you can use it in conjunction with, but you dont have to (the site says it usually isnt needed).....

mobil1 and redline are very good as well

 

[410Fortune]

Mobil one synthetic gear lube is a good alternate to Amsoil.
Most auto parts stores carry it.

Castrol makes a good synth 80W-90 too, but its harder to find.
The Mobil stuff doesnt have a wieght listed on it, but it will work in the diff on any Ford and does not require the friction addative.
I quit using the friction modifier a while back because I was told by a reputable gear shop that all it does is increase the life of the L/S and make it more quiet, but at the same time it reduces the L/S ability to grip.
So better grip, a little more noisy, and a shorter life span from the factory L/S unit, fine by me!

 

[spindlecone]

Royal Purple max gear in mine, you can google them up and use the dealer locater to find it in your local

 

[jared ajlouny]

so 75w90 is that correct weight to use?

 

[Alec]

I used 75w140 Motorcraft synth with Motorcraft LS additive.

 

[GJarrett]

Ford says use the 75w140 in the L/S, but they're the only ones making it (at about $25/qt). I and many others use the more common 75w90 which can be bought anywhere and don't have any problems whatsoever with it.

The friction modifier is also suggested but as Jamie said, it's a tradeoff: quietness and wear vs. louder and grippier, it's your choice.

 

[aldive]

so 75w90 is that correct weight to use?

Works fine for me.

 

[DocVijay]

I used the Amsoil 75w140 in mine. Like Al, I didn't add any LS additive either, and also like Al, I'm going to try it next time.

 

[snocross1985]

One more question, you guys say not putting the friction modifier in will make it louder and gripier. I know what you mean by gripier, butt what do you mean by louder? I am a little weary about not putting it in. I will be doing the mobil1 switch in the rear diff tomorrow and am considering putting the friction modifier in with it. Also should I clean the diff out at all when I drain all the gear oil out?

 

[surf]

I think Pepboys has synthetic 75w140 for $10.99 a quart.

 

[aldive]

One more question, you guys say not putting the friction modifier in will make it louder and gripier. I know what you mean by gripier, butt what do you mean by louder? I am a little weary about not putting it in. I will be doing the mobil1 switch in the rear diff tomorrow and am considering putting the friction modifier in with it. Also should I clean the diff out at all when I drain all the gear oil out?

I use Amsoil in the rear end with NO friction modifer; I hear no noise whatsoever.

 

[spindlecone]

You can get RP max gear for 9 bucks a QT and be done with it, no friction BS needed

 

[snocross1985]

should i clean the old dino gear lube out of the diff with some kind of solvent?

 

[DocVijay]

I use Amsoil in the rear end with NO friction modifer; I hear no noise whatsoever.

Like Al, I also use Amsoil without friction modifier, and I don't hear anything either. As for being "grippier," even without additive, I almost always chirp the inside tire when turning. I can't imagine it being any "grippier" without switching to a locker.

 

[aldive]

should i clean the old dino gear lube out of the diff with some kind of solvent?

Naw, just let it drain and wipe up any remaining. A solvent might get trapped in there and "harm" the new fluid.

 

[snocross1985]

ok, guess i am good to go for tomorrow. No friction modiefier and i will be going with mobil1 as i can't find any other synthetic gear oil in the stores near me and I am not about to drive 30 min to another. And just wipe out the old, got it. Thanks for your help guys.

 

[spindlecone]

If your going to remove the diff cover, than by all means clean at least the bottom of the punkin ball, if not removing the cover, is no way to clean it

 

[snocross1985]

I will be taking the cover off and wiping out the inside and the cover itself.