69MustangCoupe393cid

I didn't really know where to post this, but if it's in the wrong section mods please feel free to move it. Anyway I have a 2000GT and wan't to change the rear end fluid with some Amsoil and I have a couple questions.

1) Does anyone know if Amsoil fluids need the friction modifier; or is that something I have to ask direct about with the the specific fluid and application?

2) I know 00 calls for 80-90w, vs the 75-140w but which fluid would be the better choice for me, is either used for different reasons, why did Ford decide to switch etc.? I do mostly highway driving if that matters at all. Maybe one fluid would help get me better mileage? However whatever I do, I don't want to burn up my rear end.

cliffyk

It's 80W-90, and Ford didn't really changed the specification. It was part of a changeover from dino oil to synthetic, for 2-3 years both the 80W-90 dino and 75W-140 synthetic were listed in the specs.

In 2004 the 80W-90 was listed only for the 7.5" axle and the synthetic for the 8.8" axle.

The bottom line is that it doesn't matter. I run 75W-90 Valvoline dino juice with f/m as that's what a trusted speed shop in Daytona Beach recommended.

The Motorcraft synthetic, as with most full synthetics, does not require adding friction modifier as moly-disulfide (the main component of f/w) is a common synthetic oil additive.

As to Amsoil, if you like spending more money just for the sake of doing so then get it, otherwise just go to your FLAPS and get Mobil 1 or one of the other synthetics in either 80W-90 or 75W-140...

69MustangCoupe393cid

I'm very big on Amsoil, and I actually have some 75-140w sitting in my garage anyway, so I I'll throw that in. I'll just have to make sure it has the proper friction modifier so I don't burn my rear end up. Thanks for the info it's greatly appreciated!

cliffyk

If it's a full synthetic you won't need the f/m, as I said earlier friction modifiers are common additives in synthetic automotive oils--it's one of the ways the "miraculous" properties are attained.

You can smell the moly di-sulphide in most of them, Mobil 1 ATF reeks of it...

WhiteFoxGT

Not to shoot you down cliff.. Im sure you have researched this for days and whatnot. During my 4 years as a Ford tech and dozens of rear rebuilds, I always used the modifier with the 75-140. If it was a rear with any kind of clutch pack it got it. Everyone in the shop used it and my team leader (top tech) always made sure I had it (during my first couple rear rebuilds). Just saying.

69MustangCoupe393cid

What kind of synthetic were you putting in the rears at Ford? Maybe it has less then some other synthetics? I don't want to use to much and render my limited slip rear useless; I have traction problems as it is haha.

cliffyk

Yup, it's right here, from the 2003 owner's manual (it's in the shop manual too):



You will note that the f/m (superscript/footnote ¹) is required only for the 80W-90 dino oil, not for the 75W-140 synthetic.

This is not uncommon, nobody reads anything anymore--so how many people do you figure are driving around with traction-lock rear-ends that aren't working for crap?

----------------------------------------------
Actually the '03 specs are the only ones so annotated--from 2001 through 2004, except for 2003, they listed the 7.5 and 8.8 axles separately calling for 80W-90 dino juice in the 7.5, and the 75W-140 synthetic (with no mention of the friction modifier) in the 8.8.

You can download the owner's manuals here.

cliffyk

I spent some time going through owner's and shop manuals this morning--and it appears that only in 2002 and 2003 (I am most familiar with the 2003 specs shown above) did Ford not recommend the friction modifier with the synthetic lube. In 2001 it was recommended, for 2002 and 2003 not, then in 2004+ it's back in.

Often back-shifting like this are in response to customer complaints--it may be that the Motorcraft synthetic, used without f/m, gets grabby (which would be good IMHO) and/or noisy to an extent that the average run-of-the-mill GT buyer cannot handle (no pun intended).

It would be interesting to fill it up with the Motorcraft synthetic and no f/m and see how it behaves--I might like it...

So, it appears that both WhiteFox and myself are "correct"!

devongarver

Meh....screw it and pull a dimebag...mini spool lol.

PurpleIcedGT

I wonder how Dbag likes that mini spool..

OP - Have you replaced your Pinion Seal yet?