ATF in MT ?

[Rhymingmechanic]

MolaKule--Can Synchromesh also be used in FWD transaxles that call for ATF? I'm thinking specifically about a '94 Saturn that specs Dexron III.

On the original question, I drove a slant-six Duster that took ATF in the 3-speed. I don't know which model trans, but it was cast iron, not aluminum.

 

[mechtech2]

I am sure that ATF is used for cold weather benefits, in manual transmissions and transaxles.
Also, dealers will only have to stock one fluid for auto trans, manual trans, and power steering systems.

But no way is ATF as good as a dedicated manual transmission fluid. You don't have to go to a 140w. There are light synchromesh versions, and anything in between.

 

[Whitewolf]

Originally Posted By: Canawler
Originally Posted By: Whitewolf
ATF is a compromise .....


Wow! There's something I thought I would never read. Whitewolf saying a factory spec'ed ATF is a compromise.

What I meant was that ATF is a compromise for MT application but I think you know that.

However, ATFs are by definition a compromise because they have to do so much and the various OEMs prioritise their fluid performance needs differently according to the requirements of their individual designs and material choices. It is that very fact which causes the entire concept of the so called 'multi-vehicle ATF' to come into question (to say the very least).

As far as MTFs are concerned then my view is that the best fluid for an MT is a fluid that was designed for the MT application. That isn't simple though because the manufacturers usually validate their products with specific fluids that best work in combination with the synchro materials that they have chosen to use. Choosing to use a different fluid can work (I have done it) but you have to be VERY careful.
Any help or not?

 

[UNC017]

I keep seeing statements like:

"...strong additive packages for EP and AW qualities."

"...these fluids I believe has very low levels of EP and AW, so most vehicles are running weak fluids. "

But EP additives may be EXACTLY what the transmission designer DOES NOT WANT because they harm synchronizer friction materials. EP additives are, for the most part, needed only for differentials that have hypoid gears. No such gears exist in most manual transmissions- just spur and helical gears. Even FWDs that share a sump between diff and trans usually don't have that issue because most FWD differentials don't have hypoid gears either.

 

[Whitewolf]

Originally Posted By: 440Magnum
I keep seeing statements like:

"...strong additive packages for EP and AW qualities."

"...these fluids I believe has very low levels of EP and AW, so most vehicles are running weak fluids. "

But EP additives may be EXACTLY what the transmission designer DOES NOT WANT because they harm synchronizer friction materials. EP additives are, for the most part, needed only for differentials that have hypoid gears. No such gears exist in most manual transmissions- just spur and helical gears. Even FWDs that share a sump between diff and trans usually don't have that issue because most FWD differentials don't have hypoid gears either.


Correct. The most you need for an MT is about GL-4 level and a decent ATF can cope with that.

 

[MolaKule]

Quote:
But EP additives may be EXACTLY what the transmission designer DOES NOT WANT because they harm synchronizer friction materials. EP additives are, for the most part, needed only for differentials that have hypoid gears. No such gears exist in most manual transmissions-



Not quite correct.

Please read Post #1231225:

https://bobistheoilguy.com/forums/threads/synchromesh-manual-transmission-lubricants.93561/

There are three main additives in mt fluids: 1. EP additives for gear teeeth, 2. Anti-wear additives to reduce bearing wear, and 3. friction modifiers for the synchronizers and friction modifiers for mpg.

Minor additives are anti-foam, anti-rust, metal deactivators, anti-oxidants, detergents, and dispersants.

The metal deactivators keep the copper alloy materials from getting stained, pitted, or corroded.

Quote:
The most you need for an MT is about GL-4 level and a decent ATF can cope with that.


An ATF doesn't have GL4 levels of EP and AW additives.

Cold weather shifting and bearing/race hardenening are the only reasons designers get away with using an ATF, but again, ATF is a huge compromise.

 

[MolaKule]

Quote:
Redline and Amsoil recognize ATF is used in MTs and have formulated their products accordingly.


Really, what have they done to their formulations?

 

[Whitewolf]

As I'm sure you're aware, it is impossible to test for GL-4 performance since those tests no longer exist.

I agree that ATF usage in MTs is a compromise, in fact that's what I said.

 

[MolaKule]

While the GL-4 performance level and tests are essentially obsolete, the gear oil blender and formulator community recognize that the level of EP additives for GL-4 gear lubes have about 40% of the EP additive level and about SJ levels of AW additives compared to GL-5/MT-1 levels.

In addition, it is recognized that additional buffers and other chemical compounds are needed for GL-4 performance level mt fluids.

 

[Whitewolf]

Tell me something new!

 

[Gary Allan]

Quote:
However, ATFs are by definition a compromise because they have to do so much and the various OEMs prioritise their fluid performance needs differently according to the requirements of their individual designs and material choices.


(there's a really big smile on my face - really)

Well, this begs the question ..are you in the camp of the designers that seem to have to play a game of "top this" in fluid requirements ..or that of the alchemist that has to compensate for their obsession?

One would think that seal and/or friction material composition would be a very old challenge ..that's long been mastered. Any improvements, or so I would reason, aren't for any performance enhancements ..at least by most measures.

Then again, it's not like anyone is going to say "Well, that's it! Lay us off. We've done all that really needs to be done."

 

[UNC017]

I do not agree with the broad statement that "ATF is a compromise for a manual transmission." If the MT was designed from the get-go with ATF in mind (as were, for example, virtually all New Process/New Venture transmissions built since the early 1970s) then where is the compromise? No need for EP in GL-5 like levels, and the synchros were designed with ATF friction modifier packages in mind. ATF is absolutely up to the task of protecting GEARS, because automatic transmissions run 200,000 miles without trashing their helical-cut planetary sets just fine.

Now I personally own an example of a transmission that is pretty much screwed and has to run a compromise fluid these days: the 97-up Aisin-Warner AX-15 in my '99 Jeep. For reasons known only to the idjits at Aisin, the synchro materials in the AX-15 were changed from being GL-5 compatible to GL-5 non-compatible in 1997. GL-3 fluid was recommended at the time these transmissions were built 10-13 years ago, but is now virtually unobtainable. So Chrysler is stuck, and ultimately wound up issuing a service bulletin recommending (hold on to your hat...) 10w30 or 10w40 engine oil for that particular transmission. Of course Redline MT-90 is probably a better choice still, but I'm starting to get synchro issues in first gear even with MT-90, probably because the previous owner used Jiffy Lube for all his fluid changes and I'm certain they filled it up with bulk GL-5 on several occasions.

No WONDER Chrysler ditched Aisin and put the NV3550 in its place in the Jeep line starting in 2000. And when my Aisin breaks, a NV3550 WILL be going in its place.

 

[MolaKule]

Quote:
No need for EP in GL-5 like levels, and the synchros were designed with ATF friction modifier packages in mind.


I never said we needed GL-5 like levels of EP additive. Even gears cut for low noise level operation need protection.

Friction modifiers for automatic and manual transmissions are totally different chemical compounds. While both the metallic synchronizers and pressure plate systems are forms of clutches, each has it's own frictional characteristics.

AT's are forced convection cooled when in operation and mt's are not, which requires different protecton additives as well.

 

[d00df00d]

So, assuming a transmission that has been competently developed and thoroughly tested with ATF, what is the harm in using a true ATF rather than an MTL with ATF-like viscosity? Is it simply a sub-optimal result, or is there more to it than that?

 

[MolaKule]

IMHO, a sub-optimal result.

I would use ATF for the warranty period and then switch to Pennzoil or GM Synchromesh.

 

[MolaKule]

Quote:
...and the synchros were designed with ATF friction modifier packages in mind...


What was the material used for the synchronizer assembly and what type of design is used?

 

[MolaKule]

Quote:
MolaKule--Can Synchromesh also be used in FWD transaxles that call for ATF? I'm thinking specifically about a '94 Saturn that specs Dexron III.


I don't see why not. Try it and let us know how it shifts over one seasion.

 

[MolaKule]

Quote:
For reasons known only to the idjits at Aisin, the synchro materials in the AX-15 were changed from being GL-5 compatible to GL-5 non-compatible in 1997. GL-3 fluid was recommended at the time these transmissions were built 10-13 years ago, but is now virtually unobtainable. So Chrysler is stuck, and ultimately wound up issuing a service bulletin recommending (hold on to your hat...) 10w30 or 10w40 engine oil for that particular transmission. Of course Redline MT-90 is probably a better choice still, but I'm starting to get synchro issues in first gear even with MT-90, probably because the previous owner used Jiffy Lube for all his fluid changes and I'm certain they filled it up with bulk GL-5 on several occasions.


With a previous owner you never know what kind of lubes they used, and as per the link I gave, I was never comfortable with using diffy fluid in an MT.

The Aisin case is another one of those in which the engineers did not consult with the tribologist or lubrication engineer during the design or testing phase. This happens more than you might imagine and then when field failures start coming in, they scramble to dump somethiong in there until they figure out what they screwed up.

 

[Jim Allen]

Thread Hijack!

MolaKule: What is your opinion on using a synthetic GL-5 grade 90 in a trans that specs a 90 (at least that's what the tractor dealer says). Specifically, I have a small Ford tractor that specs a Ford M2C-86-B. My manual does not list the viscosity of that oil, though the dealer says they use a 8W90 in them. I kinda have my doubts as to that being correct. The trans is separate from the rear axle.hyd reservoir. It's not been an issue but the trans is now due for a change and I happen to have some old Series 2000 Amsoil in 75W90 and I noted stiff shifting this frigid winter when working the tractor.

 

[UNC017]

Originally Posted By: d00df00d
So, assuming a transmission that has been competently developed and thoroughly tested with ATF, what is the harm in using a true ATF rather than an MTL with ATF-like viscosity? Is it simply a sub-optimal result, or is there more to it than that?


My point exactly. If the MT was designed ground-up for ATF, then I see absolutely no compromise in using ATF in it. OTOH, if it was designed for GL-3 then re-specced for ATF to cure hard shifting in cold weather (its been done) then there is obviously much more chance of a compromise.

People keep throwing out claims to the effect that automatics and manuals inherently have completely different requirements, but that is ONLY true if the manual was not designed with ATF in mind. The friction characteristics of a synchro can be (and I would say often are) made to be practically identical to the friction requirements of an automatic's multi-plate clutch packs with the right choice of materials and geometry. Now when you start talking about anti-shudder additives that drastically lower the static coefficient of friction to let TC lockup clutches engage smoothly (eg. Mopar ATF+3 and ATF+4) then the will probably be different and the MT might get a case of indigestion if its designer wasn't expecting that additive in the fluid.