GT06GT

Hey all,

Do I need to still add friction modifier to the diff even though mobil 1 75w140 states that it comes with friction modifier in it? Ford calls for 4 oz of it but im not able to tell how much is already in mobil 1

onederful100

dont take my opinion as gospel, but since the mobil 1 has the modifier in it already i dont see a need to add more.

jwharton

I think you will find that you will be adding it after listening to your rear end cry, moan and pop when turning corners. GM rear ends seem to get by fine with synthetics and no modifier...but Fords don't. Hope I'm wrong, but from my own and a few others I've talked to.....you will need it. It's only $5.00 at Ford.
Good Luck!

jayed53

I dont know about the mobil 1, but I changed out the fluid a while back with RP 75-140 and my diff has been quiet, with no issues. I have heard others with after market 4.10s that have had huge issues without it however, so not sure.

6-Speed

Yep, Royal Purple Maxgear has friction modifiers in its formula, so I didn't add any more. No problems with noise.

GT06GT

any damage possible if to much is put in? (4oz that ford calls for + whatever is in mobil 1)

07 GT E UPP

When it comes to a rear gear install, for the sake of $5.00-$6.00 I prefer to play it on the safe side and add a separate bottle of friction modifier.

NJBLK07GT

For what it's worth, I did RP to my rear a few weeks ago and added a bottle of Ford modifier just to be safe. All has been quiet since. I'd add it just to be safe......it can't hurt.

Nuke

I think I have to agree with the majority so far, including input from other threads on this subject. I'd add the modifier rather than wait for an issue. Or at least have it on hand so you can add it at the onset of the symptomatic noise.

discodave

How much are you guys paying to have the rear diff fluid changed? I got quoted 300 bucks from a local shop and that sound like highway robbery to me.