Originally posted by todras:
Terry just sent me this. He's been discussing the issue with some colleagues that work as "lube" engineers.

....info so far from 'Karl'(Germany),'Mike' (UK) &
'Ryan' (USA).
The overall take is that 'GL' additives are all a
problem in a trans with a)ally case b)brass bronze
blockers etc.The majority of GL additives are sulphur
based.This varies in %'age but does have a corrosive
effect on the brass blockers,be it slow.All agree that
the 'grey'/black paste is a result of the additives on
the ally case causing oxide.
ATF fluids dare not have any sulphur additive due to
the paste (re valve bodies in autos)and a lot of autos
also use brass/bronze bushings.
It appears the guts of the problem is sulphur.
Points against ATF...it does not like high gear tooth
pressures and can break down in high tooth pressure
designs(Re straight cut,semi-helical & hypoid gear
cuts),the MTX 75 has helical gear cut(lower tooth
pressures),except in the 'stoc' open diff gears ,which
are straight cut.This may expalain why some owners
feel the HP lube may save the diff gears.Should add my
2 cents here that the pre 98 diffs were 'fully' cut
gears Vs the later moulded/sintered diff gears.I have
never seen the early 'cut' gears fail,a diff pinion
pin yes but not the gears and most of these have run
straight ATF all the time (it was factory fill).
Examples ,an MTX with stoc gears and a Quaife/Torsen
diff = ATF or current Ford spec honey.
An MTX with Quaife 'syncro' gear set(which have a
semi-helical gear cut) and a Quaife diff =75W90
G4....this shows that the gear tooth pressure on a
semi-helical cut needs EP additives plus you will get
some grey residue but the EP is for the main gears not
the Quaife/Torsen diff.
Last extreme would be a Quaife 'dog gear' set that has
straight cut gears,no brass blockers(uses steel dogs')
and a Quaife diff =75W90 GL4/5, a higher GL rating for
the even higher gear tooth pressures of a straight cut
gears over a semi-helical or helical cut.
We still have some more info from all three to
come....Just a point to note,the MTL spec sheet on
it's benefits list *Satisfies manual transmissions and
transaxles requiring motor oils(engine) or GL-1,GL-3
or GL-4 gear oils. The MTX75 has never been spec'd
with motor oils or any GL type gear lubes,the only two
lubes have been ATF then 'honey(as a retro fill back
to '95)...



I can tell you right now that the part about the grey paste not being caused by ATF is incorrect.

I started my transmission work working on automatic transmissions; ford, chrysler, and GM. There is a serious amount of grey paste that accumulates in any automatic with around 1.5 years or more on the fluid and/or 25K miles or more, in almost every case! Why do you think they filter an automatic trans and don't filter a manual even though they both can use ATF? The valve body as Terry pointed out can't have a buildup whereas it is no big deal with the manual.
The ATF and lack of corrosives plays no roll as it is from the metal wear and the clutch and band material being worn off through time that the paste is caused in an ATX. In an MTX it is also through metal wear.
I'm intrigued that there can be the same paste buildup in a Transmission that uses ATF, be it an mtx or atx and yet THAT isn't called corrosion. It looks the same and can be wiped free.

I suspect all we are seeing is abnormally high metallic wear from the Torsen and or from the weak stock diff.

Anyone on here see any gray film/paste on theirATX, or on their MTX when the took it apart to put in shift forks and/or an LSD after using ATF? Or can we assume that everyone using ATF experienced NO gray metallic paste??

Oh, by the way. When was the last time that non-helical cut gears were used in transmissions and rear ends outside of higher performance racing or specific applications? I"ll give you a hint, like 1940!!
The manufacturers figured out that helical cut transfered the contact from one tooth to another continuously and made a much quieter operation. Straight cut gears are actually stronger but the downside is the noise. THe noise was so bad that the designers came up with helical cut.

This means....ALL factory differentials come with helical cut gears even in heavy duty work equipment other than special applications like racing based solely on high frequency noise and the resultant hearing loss. THOSE differentials and gear boxes, the helical cut industrial ones, were wearing out too fast and GL additives were developed to protect them from the high loads. All heavy rear ends call for GL-5 after it came out but the corrosion to brass prevents it from being used in transmissions. Nothing is said about the aluminum.

Another point. THe aluminum is protected by a layer of aluminum oxide. All alumimun without annodizing and coatings is protected by this 'Alumina' to some degree as it forms naturally as oxygen in the air corrodes the aluminum. The process will continue over time if left to the air uncoated (look at an aluminum rim without paint). After a while the process slows down because the oxygen can't penetrate the layers of alumina that form on the aluminum. Aluminum Oxide is one of the most chemically resistive, or chemically inert compounds known! To be corroded by oil additives is a bit of a stretch.
Look it up! Now you are getting into my area of expertise as a Materials Engineer. Alumina or aluminum oxide is VERY resistant to all kinds of corrosives. IT isn't perfect but I'd bet it can handle oil/oil additives and I know it can handle moisture. You don't think the GL-4/5 would list aluminum on the corrosive list if it wasn't an issue? That leaves only the brass and I don't think the brass will leave that color and kind of residue.
I'll look into it though.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black